Found 51 papers in cond-mat
Date of feed: Tue, 06 Jun 2023 00:30:00 GMT

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Twist-Induced Hyperbolic Shear Metasurfaces. (arXiv:2306.01775v1 [cond-mat.mes-hall])
Simon Yves, Emanuele Galiffi, Xiang Ni, Enrico Maria Renzi, Andrea Alù

Following the discovery of moir\'e-driven superconductivity in twisted graphene multilayers, twistronics has spurred a surge of interest in tailored broken symmetries through angular rotations, enabling new properties from electronics to photonics and phononics. Analogously, in monoclinic polar crystals a nontrivial angle between non-degenerate dipolar phonon resonances can naturally emerge due to asymmetries in their crystal lattice, and its variations are associated with intriguing polaritonic phenomena, including axial dispersion, i.e., a rotation of the optical axis with frequency, and microscopic shear effects that result in asymmetric loss distributions. So far these phenomena were restricted to specific mid-infrared frequencies, difficult to access with conventional lasers, and fundamentally limited by the degree of asymmetry and the strength of light-matter interactions available in natural crystals. Here, we leverage twistronics to demonstrate giant axial dispersion and loss asymmetry of hyperbolic waves in elastic metasurfaces, by tailoring the angle between coupled pairs of anisotropic metasurfaces. We show extreme control over elastic wave dispersion via the twist angle, and leverage the resulting phenomena to demonstrate reflection-free negative refraction, as well as the application of axial dispersion to achieve diffraction-free non-destructive testing, whereby the angular direction of a hyperbolic probe wave is encoded into its frequency. Our work welds the concepts of twistronics, non-Hermiticity and extreme anisotropy, demonstrating the powerful opportunities enabled by metasurfaces for tunable, highly directional surface acoustic wave propagation, of great interest for applications ranging from seismic mitigation to on-chip phononics and wireless communications, paving the way towards their translation into emerging photonic and polaritonic metasurface technologies.


Interaction induced AC-Stark shift of exciton-polaron resonances. (arXiv:2306.01778v1 [cond-mat.mes-hall])
Takahiro Uto, Bertrand Evrard, Kenji Watanabe, Takashi Taniguchi, Martin Kroner, Atac Imamoglu

Laser induced shift of atomic states due to the AC-Stark effect has played a central role in cold-atom physics and facilitated their emergence as analog quantum simulators. Here, we explore this phenomena in an atomically thin layer of semiconductor MoSe$_2$, which we embedded in a heterostructure enabling charge tunability. Shining an intense pump laser with a small detuning from the material resonances, we generate a large population of virtual collective excitations, and achieve a regime where interactions with this background population is the leading contribution to the AC-Stark shift. Using this technique we study how itinerant charges modify -- and dramatically enhance -- the interactions between optical excitations. In particular, our experiments show that the interaction between attractive polarons could be two orders of magnitude stronger than those between bare excitons.


Emergence of collective self-oscillations in minimal lattice models with feedback. (arXiv:2306.01823v1 [cond-mat.stat-mech])
Dmitry Sinelschikov, Anna Poggialini, Maria Francesca Abbate, Daniele De Martino

The emergence of collective oscillations and synchronization is a widespread phenomenon in complex systems. While widely studied in dynamical systems theory, this phenomenon is not well understood in the context of out-of-equilibrium phase transitions. Here we consider classical lattice models, namely the Ising, the Blume-Capel and the Potts models, with a feedback among the order and control parameters. With linear response theory we derive low-dimensional dynamical systems for mean field cases that quantitatively reproduce many-body stochastic simulations. In general, we find that the usual equilibrium phase transitions are taken over by complex bifurcations where self-oscillations emerge, a behavior that we illustrate by the feedback Landau theory. For the case of the Ising model, we obtain that the bifurcation that takes over the critical point is non-trivial in finite dimensions. We provide numerical evidence that in 2D the most probable value of the amplitude follows the Onsager law. We illustrate multi-stability for the case of discontinuously emerging oscillations in the Blume-Capel model, whose tricritical point is substituted by the Bautin bifurcation. For the Potts model with q = 3 colors we highlight the appearance of two mirror stable limit cycles at a bifurcation line and characterize the onset of chaotic oscillations that emerge at low temperature through either the Feigenbaum cascade of period doubling or the Aifraimovich-Shilnikov scenario of a torus destruction. We show that entropy production singularities as a function of the temperature correspond to change in the spectrum of Lyapunov exponents. Our results show that mean-field behaviour can be described by the bifurcation theory of low-dimensional dynamical systems, which paves the way for the definition of universality classes of collective oscillations.


Terahertz bolometric detectors based on graphene field-effect transistors with the composite h-BN/black-P/h-BN gate layers using plasmonic resonances. (arXiv:2306.01975v1 [cond-mat.mes-hall])
M. Ryzhii, V. Ryzhii, M. S. Shur, V. Mitin, C. Tang, T. Otsuji

We propose and analyze the performance of terahertz (THz) room-temperature bolometric detectors based on the graphene channel field-effect transistors (GC-FET). These detectors comprise the gate barrier layer (BL) composed of the lateral hexagonal-Boron Nitride black-Phosphorus/ hexagonal-Boron Nitride (h-BN/b-P/h-BN) structure. The main part of the GC is encapsulated in h-BN, whereas a short section of the GC is sandwiched between the b-P gate BL and the h-BN bottom layer. The b-P gate BL serves as the window for the electron thermionic current from the GC. The electron mobility in the GC section encapsulated in h-BN can be fairly large. This might enable a strong resonant plasmonic response of the GC-FET detectors despite relatively lower electron mobility in the GC section covered by the b-P window BL. The narrow b-P window diminishes the Peltier cooling and enhances the detector performance. The proposed device structure and its operation principle promote elevated values of the room-temperature GC-FET THz detector responsivity and other characteristics, especially at the plasmonic resonances.


Two types of zero Hall phenomena in few-layer MnBi$_2$Te$_4$. (arXiv:2306.02046v1 [cond-mat.mes-hall])
Yaoxin Li, Yongchao Wang, Zichen Lian, Hao Li, Zhiting Gao, Liangcai Xu, Huan Wang, Ruie Lu, Longfei Li, Yang Feng, Tianlong Xia, Chang Liu, Shuang Jia, Yang Wu, Jinsong Zhang, Chang Liu, Yayu Wang

The van der Waals antiferromagnetic topological insulator MnBi$_2$Te$_4$ represents a promising platform for exploring the layer-dependent magnetism and topological states of matter. Despite the realization of several quantized phenomena, such as the quantum anomalous Hall effect and the axion insulator state, the recently observed discrepancies between magnetic and transport properties have aroused controversies concerning the topological nature of MnBi$_2$Te$_4$ in the ground state. Here, we demonstrate the existence of two distinct types of zero Hall phenomena in few-layer MnBi$_2$Te$_4$. In addition to the robust zero Hall plateau associated with the axion insulator state, an unexpected zero Hall phenomenon also occurs in some odd-number-septuple layer devices. Importantly, a statistical survey of the optical contrast in more than 200 MnBi$_2$Te$_4$ reveals that such accidental zero Hall phenomenon arises from the reduction of effective thickness during fabrication process, a factor that was rarely noticed in previous studies of 2D materials. Our finding not only resolves the controversies on the relation between magnetism and anomalous Hall effect in MnBi$_2$Te$_4$, but also highlights the critical issues concerning the fabrication and characterization of devices based on 2D materials.


Thomas-Fermi theory of out-of-plane charge screening in graphene. (arXiv:2306.02103v1 [math.AP])
Vitaly Moroz, Cyrill B. Muratov

This paper provides a variational treatment of the effect of external charges on the free charges in an infinite free-standing graphene sheet within the Thomas-Fermi theory. We establish existence, uniqueness and regularity of the energy minimizers corresponding to the free charge densities that screen the effect of an external electrostatic potential at the neutrality point. For the potential due to one or several off-layer point charges, we also prove positivity and a precise universal asymptotic decay rate for the screening charge density, as well as an exact charge cancellation by the graphene sheet. We also treat a simpler case of the non-zero background charge density and establish similar results in that case.


Observation of time-reversal symmetry breaking in the band structure of altermagnetic RuO$_2$. (arXiv:2306.02170v1 [cond-mat.mtrl-sci])
O. Fedchenko, J. Minar, A. Akashdeep, S.W. D'Souza, D. Vasilyev, O. Tkach, L. Odenbreit, Q.L. Nguyen, D. Kutnyakhov, N. Wind, L. Wenthaus, M. Scholz, K. Rossnagel, M. Hoesch, M. Aeschlimann, B. Stadtmueller, M. Klaeui, G. Schoenhense, G. Jakob, T. Jungwirth, L. Smejkal, J. Sinova, H. J. Elmers

Altermagnets are an emerging third elementary class of magnets. Unlike ferromagnets, their distinct crystal symmetries inhibit magnetization while, unlike antiferromagnets, they promote strong spin polarization in the band structure. The corresponding unconventional mechanism of timereversal symmetry breaking without magnetization in the electronic spectra has been regarded as a primary signature of altermagnetism, but has not been experimentally visualized to date. We directly observe strong time-reversal symmetry breaking in the band structure of altermagnetic RuO$_2$ by detecting magnetic circular dichroism in angle-resolved photoemission spectra. Our experimental results, supported by ab initio calculations, establish the microscopic electronic-structure basis for a family of novel phenomena and functionalities in fields ranging from topological matter to spintronics, that are based on the unconventional time-reversal symmetry breaking in altermagnets.


Average Symmetry Protected Higher-order Topological Amorphous Insulators. (arXiv:2306.02246v1 [cond-mat.dis-nn])
Yu-Liang Tao, Jiong-Hao Wang, Yong Xu

While topological phases have been extensively studied in amorphous systems in recent years, it remains unclear whether the random nature of amorphous materials can give rise to higher-order topological phases that have no crystalline counterparts. Here we theoretically demonstrate the existence of higher-order topological insulators in two-dimensional amorphous systems that can host more than six corner modes, such as eight or twelve corner modes. Although individual sample configuration lacks crystalline symmetry, we find that an ensemble of all configurations exhibits an average crystalline symmetry that provides protection for the new topological phases. To characterize the topological phases, we construct two topological invariants. Even though the bulk energy gap in the topological phase vanishes in the thermodynamic limit, we show that the bulk states near zero energy are localized, as supported by the level-spacing statistics. Our findings open an avenue for exploring average symmetry protected higher-order topological phases in amorphous systems without crystalline counterparts.


Theory of exciton-polariton condensation in gap-confined eigenmodes. (arXiv:2306.02281v1 [cond-mat.other])
Davide Nigro ad Dario Gerace

Exciton-polaritons are bosonic-like elementary excitations in semiconductors, which have been recently shown to display large occupancy of topologically protected polariton bound states in the continuum in suitably engineered photonic lattices [Nature {\bf 605}, 447 (2022)], compatible with the definition of polariton condensation. However, a full theoretical description of such condensation mechanism that is based on a non equilibrium Gross-Pitaevskii formulation is still missing. Given that the latter is well known to account for polariton condensation in conventional semiconductor microcavities, here we report on its multi-mode generalization, showing that it allows to fully interpret the recent experimental findings in patterned photonic lattices, including emission characteristics and condensation thresholds. Beyond that, it is shown that the polariton condensation in these systems is actually the result of an interplay between negative mass confinement of polariton eigenstates (e.g., due to the photonic gap originated from the periodic pattern in plane) and polariton losses. We are then able to show that polariton condensation can also occur in gap-confined bright modes, i.e., coupling of QW excitons to a dark photonic mode is not necessarily required to achieve a macroscopic occupation with low population threshold.


Generation of Circularly-Polarised High-Harmonics with Identical Helicity in Two-Dimensional Materials. (arXiv:2306.02313v1 [physics.optics])
Navdeep Rana, M. S. Mrudul, Gopal Dixit

Generation of circularly-polarized high-harmonics with the same helicity to all orders is indispensable for chiral-sensitive spectroscopy with attosecond temporal resolution. Solid-state samples have added a valuable asset in controlling the polarization of emitted harmonics. However, maintaining the identical helicity of the emitted harmonics to all orders is a daunting task. In this work, we demonstrate a robust recipe for efficient generation of circularly-polarized harmonics with the same helicity. For this purpose, a nontrivial tailored driving field, consisting of two co-rotating laser pulses with frequencies $\omega$ and $2\omega$, is utilized to generate harmonics from graphene. The Lissajous figure of the total driving pulse exhibits an absence of the rotational symmetry, which imposes no constraint on the helicity of the emitted harmonics. Our approach to generating circularly-polarized harmonics with the same helicity is robust against various perturbations in the setup, such as variation in the subcycle phase difference or the intensity ratio of the $\omega$ and $2\omega$ pulses, as rotational symmetry of the total driving pulse remains absent. Our approach is expected to be equally applicable to other two-dimensional materials, among others, transition-metal dichalcogenides and hexagonal boron nitride as our approach is based on absence of the rotational symmetry of the driving pulse. Our work paves the way for establishing compact solid-state chiral-XUV sources, opening a new realm for chiral light-matter interaction on its intrinsic timescale.


Real higher-order Weyl photonic crystal. (arXiv:2306.02321v1 [cond-mat.mes-hall])
Yuang Pan, Chaoxi Cui, Qiaolu Chen, Fujia Chen, Li Zhang, Yudong Ren, Ning Han, Wenhao Li, Xinrui Li, Zhi-Ming Yu, Hongsheng Chen, Yihao Yang

Higher-order Weyl semimetals are a family of recently predicted topological phases simultaneously showcasing unconventional properties derived from Weyl points, such as chiral anomaly, and multidimensional topological phenomena originating from higher-order topology. The higher-order Weyl semimetal phases, with their higher-order topology arising from quantized dipole or quadrupole bulk polarizations, have been demonstrated in phononics and circuits. Here, we experimentally discover a class of higher-order Weyl semimetal phase in a three-dimensional photonic crystal (PhC), exhibiting the concurrence of the surface and hinge Fermi arcs from the nonzero Chern number and the nontrivial generalized real Chern number, respectively, coined a real higher-order Weyl PhC. Notably, the projected two-dimensional subsystem with kz = 0 is a real Chern insulator, belonging to the Stiefel-Whitney class with real Bloch wavefunctions, which is distinguished fundamentally from the Chern class with complex Bloch wavefunctions. Our work offers an ideal photonic platform for exploring potential applications and material properties associated with the higher-order Weyl points and the Stiefel-Whitney class of topological phases.


Perturbation-induced granular fluidization as a model for remote earthquake triggering. (arXiv:2306.02353v1 [cond-mat.soft])
Kasra Farain, Daniel Bonn

Studying the effect of mechanical perturbations on granular systems is crucial for understanding soil stability, avalanches, and earthquakes. We investigate a granular system as a laboratory proxy for fault gouge. When subjected to a slow shear, granular materials typically exhibit a stress overshoot before reaching a steady state. We find that short seismic pulses can reset a granular system flowing in steady state so that the stress overshoot is regenerated. This new feature is shown to determine the stability of the granular system under different applied stresses in the wake of a perturbation pulse and the resulting dynamics when it fails. Using an analytical aging-rejuvenation model for describing the overshoot response, we show that our laboratory-derived theoretical framework, can quantitatively explain data from two fault slip events triggered by seismic waves.


Performance of near-optimal protocols in weak processes. (arXiv:2306.02483v1 [cond-mat.stat-mech])
Pierre Nazé

A natural criticism of the universal optimal protocol of the irreversible work found in the context of weak processes is its experimental difficulty to be implementable due to its singular part. In this work, I propose as a partial solution to this problem its continuous linear part as an acceptable near-optimal protocol. This is based on the analysis of several examples of the error committed to approximating the solution extended until its second order in its continuous linear part. The result seems to be universal: depending mainly on the ratio between switching time and waiting time $\tau/\tau_w$, the error for sudden and slowly-varying processes is less than $1\%$, while for $\tau\approx\tau_w$ it has a peak with an upper bound around $8\%$. Although implementing Dirac deltas could be an experimental challenge, I present also the error including those functions, where the results of these new near-optimal protocols become slightly better.


Study of gapped phases of 4d gauge theories using temporal gauging of the $\mathbb{Z}_N$ 1-form symmetry. (arXiv:2306.02485v1 [hep-th])
Mendel Nguyen, Yuya Tanizaki, Mithat Ünsal

To study gapped phases of $4$d gauge theories, we introduce the temporal gauging of $\mathbb{Z}_N$ $1$-form symmetry in $4$d quantum field theories (QFTs), thereby defining effective $3$d QFTs with $\widetilde{\mathbb{Z}}_N\times \mathbb{Z}_N$ $1$-form symmetry. In this way, spatial fundamental Wilson and 't Hooft loops are simultaneously genuine line operators. Assuming a mass gap and Lorentz invariant vacuum of the $4$d QFT, the $\widetilde{\mathbb{Z}}_N\times \mathbb{Z}_N$ symmetry must be spontaneously broken to an order-$N$ subgroup $H$, and we can classify the $4$d gapped phases by specifying $H$. This establishes the $1$-to-$1$ correspondence between the two classification schemes for gapped phases of $4$d gauge theories: One is the conventional Wilson-'t Hooft classification, and the other is the modern classification using the spontaneous breaking of $4$d $1$-form symmetry enriched with symmetry-protected topological states.


Topological magnets and magnons in twisted bilayer MoTe$_2$ and WSe$_2$. (arXiv:2306.02501v1 [cond-mat.str-el])
Taige Wang, Trithep Devakul, Michael P. Zaletel, Liang Fu

Twisted homobilayer transition metal dichalcogenide (TMD) offer a versatile platform for exploring band topology, correlated phases, and magnetic orders. We study the correlated phases in twisted TMD homobilayers and their low energy collective excitations, focusing on the effect of band topology on magnetism and thermal stability. From Hartree-Fock theory of the continuum model, we identify several magnetic and topological phases. By tuning the displacement field, we find two phase transitions involving a change in topology and magnetism respectively. We analyze the magnon spectrum, revealing the crucial role of band topology in stabilizing 2D ferromagnetism by amplifying easy-axis magnetic anisotropy, resulting in a large magnon gap of up to 7meV. As the magnon gap is directly tied to the stability of the magnetic phase to thermal fluctuations, our findings have several important experimental implications.


Topological phase transitions in a honeycomb ferromagnet with unequal Dzyaloshinskii-Moriya interactions. (arXiv:2306.02505v1 [cond-mat.other])
Heng Zhu, Hongchao Shi, Zhengguo Tang, Bing Tang

This theoretical research is devoted to study topological phase transitions in a two-dimensional honeycomb ferromagnetic lattice with unequal Dzyaloshinskii-Moriya interactions for the two sublattices. With the help of a first-order Green function formalism, we analyze the influence of magnon-magnon interaction on the magnon band topology. It is found that the existence of the antichiral Dzyaloshinskii-Moriya interaction can led to a tilting of the renormalized magnon bands near the Dirac momenta. Then, the renormalized magnon band gaps at Dirac points have different widths. Through changing the temperature, we can observe the renormalized magnon band gap closing-reopening phenomenon, which corresponds to the topological phase transition. Our results show that the critical temperature of the topological phase transition is related to the strength of the antichiral Dzyaloshinskii-Moriya interaction.


Zero-field composite Fermi liquid in twisted semiconductor bilayers. (arXiv:2306.02513v1 [cond-mat.mes-hall])
Hart Goldman, Aidan P. Reddy, Nisarga Paul, Liang Fu

Recent experiments have produced evidence for fractional quantum anomalous Hall (FQAH) states at zero magnetic field in the semiconductor moir\'e superlattice system $t$MoTe$_2$. Here we argue that a composite fermion description, already a unifying framework for the phenomenology of 2d electron gases at high magnetic fields, provides a similarly powerful perspective in this new context, despite the absence of a magnetic field. To this end, we present exact diagonalization evidence for composite Fermi liquid states at zero magnetic field in $t$MoTe$_2$, at fillings $n=\frac{1}{2}$ and $n=\frac{3}{4}$. We dub these non-Fermi liquid metals anomalous composite Fermi liquids (ACFLs), and we argue that they play a central organizing role in the FQAH phase diagram. We proceed to develop a long wavelength theory for this ACFL state, which offers concrete experimental predictions upon doping the composite Fermi sea, including a Jain sequence of FQAH states and a new type of commensurability oscillations originating from the superlattice potential intrinsic to the system.


Spin-orbit torque generation in bilayers composed of CoFeB and epitaxial SrIrO$_{3}$ grown on an orthorhombic DyScO$_{3}$ substrate. (arXiv:2306.02567v1 [cond-mat.mtrl-sci])
Sosuke Hori, Kohei Ueda, Takanori Kida, Masayuki Hagiwara, Jobu Matsuno

We report on the highly efficient spin-orbit torque (SOT) generation in epitaxial SrIrO$_{3}$(SIO), which is grown on an orthorhombic DyScO$_{3}$(110) substrate. By conducting harmonic Hall measurement in Co$_{20}$Fe$_{60}$B$_{20}$ (CoFeB)/SIO bilayers, we characterize two kinds of the SOTs, i.e., dampinglike (DL) and fieldlike ones to find that the former is much larger than the latter. By comparison with the Pt control sample with the same CoFeB thickness, the observed DL SOT efficiency $\xi$$_{DL}$ of SIO ($\sim$0.32) is three times higher than that of Pt ($\sim$0.093). The $\xi$$_{DL}$ is nearly constant as a function of the CoFeB thickness, suggesting that the SIO plays a crucial role in the large SOT generation. These results on the CoFeB/SIO bilayers highlight that the epitaxial SIO is promising for low-current and reliable spin-orbit torque-controlled devices.


A Non-topological Extension of Bending-immune Valley Topological Edge States. (arXiv:2306.02633v1 [physics.optics])
Tianyuan Liu, Wei Yan, Min Qiu

Breaking parity (P) symmetry in C6 symmetric crystals is a common routine to implement a valley-topological phase. At an interface between two crystals of opposite valley phases, the so-called valley topological edge states emerge, and they have been proven useful for wave transport with robustness against 120 degree bending and a certain level of disorder. However, whether these attractive transport features are bound with the valley topology or due to topological-irrelevant mechanisms remains unclear. In this letter, we discuss this question by examining transport properties of photonic edge states with varied degrees of the P-breaking that tune the valley topology, and reveal that the edge states preserve their transport robustness insensitive to the topology even when the P-symmetry is recovered. Instead, a unique modal character of the edge states--with localized momentum hotspots around high-symmetric K (K') points--is recognized to play the key role, which only concerns the existence of the valleys in the bulk band structures, and has no special requirement on the topology. The "non-topological" notion of valley edge states is introduced to conceptualize this modal character, leading to a coherent understanding of bending immunity in a range of edge modes implemented in C3 symmetric crystals--such as valley topological edge states, topological edge states of 2D Zak phase, topological-trivial edge states and so on--, and to new designs in general rhombic lattices--with exemplified bending angle as large as 150 degree.


Quantum Valley and Sub-valley Hall Effect in the Large Angle Twisted Bilayer Graphene. (arXiv:2306.02655v1 [cond-mat.mes-hall])
Chiranjit Mondal, Rasoul Ghadimi, Bohm-Jung Yang

We study the quantum valley Hall effect and related domain wall modes in twisted bilayer graphene at a large commensurate angle. Due to the quantum valley and sub-valley Hall effect, a small deviation from the commensurate angle generates two-dimensional conducting network patterns composed of one-dimensional domain wall conducting channels, which can induce non-Fermi liquid transport behavior within an accessible temperature range. The domain wall modes can be manipulated by using the layer shifting and external electric fields which, in turn, leads to the sub-valley Haldane and Semenoff masses on the domain wall modes. The large-angle twisted bilayer graphene and related materials can be a new setup to harness the quantum valley and sub-valley Hall effect with enhanced tunability.


Non-equilibrium dynamics of spin-lattice coupling. (arXiv:2306.02676v1 [cond-mat.str-el])
Hiroki Ueda, Roman Mankowsky, Eugenio Paris, Mathias Sander, Yunpei Deng, Biaolong Liu, Ludmila Leroy, Abhishek Nag, Elizabeth Skoropata, Chennan Wang Victor Ukleev, Gérard Sylvester Perren, Janine Dössegger, Sabina Gurung, Elsa Abreu, Matteo Savoini, Tsuyoshi Kimura, Luc Patthey, Elia Razzoli, Henrik Till Lemke, Steven Lee Johnson, Urs Staub

Interactions between the different degrees of freedom form the basis of many manifestations of intriguing physics in condensed matter. In this respect, quantifying the dynamics of normal modes that themselves arise from these interactions and how they interact with other excitations is of central importance. Of the different types of coupling that are often important, spin-lattice coupling is relevant to several sub-fields of condensed matter physics; examples include spintronics, high-TC superconductivity, and topological materials. While theories of materials where spin-lattice coupling is relevant can sometimes be used to infer the magnitude and character of this interaction, experimental approaches that can directly measure it are rare and incomplete. Here we use time-resolved X-ray diffraction to directly access the spin-lattice coupling by measuring both ultrafast atomic motion and the associated spin dynamics following the excitation of a coherent electromagnon by an intense THz pulse in a multiferroic hexaferrite. Comparing the dynamics of the two different components, one striking outcome is the different phase shifts relative to the driving field. This phase shift provides insight into the excitation process of such a coupled mode. This direct observation of combined lattice and magnetization dynamics paves the way to access the mode-selective spin-lattice coupling strength, which remains a missing fundamental parameter for ultrafast control of magnetism and is relevant to a wide variety of correlated electron physics.


All-Optical Ultrafast Valley Switching in Two-Dimensional Materials. (arXiv:2306.02856v1 [physics.optics])
Navdeep Rana, Gopal Dixit

Electrons in two-dimensional materials possess an additional quantum attribute, the valley pseudospin, labelled as $\mathbf{K}$ and $\mathbf{K}^{\prime}$ -- analogous to the spin up and spin down. The majority of research to achieve valley-selective excitations in valleytronics depends on resonant circularly-polarised light with a given helicity. Not only acquiring valley-selective electron excitation but also switching the excitation from one valley to another is quintessential for bringing valleytronics-based technologies in reality. Present work introduces a coherent control protocol to initiate valley-selective excitation, de-excitation, and switch the excitation from one valley to another on the fly within tens of femtoseconds -- a timescale faster than any valley decoherence time. Our protocol is equally applicable to {\it both} gapped and gapless two-dimensional materials. Monolayer graphene and molybdenum disulfide are used to test the universality. Moreover, the protocol is robust as it is insensitive to significant parameters of the protocol, such as dephasing times, wavelengths, and time delays of the laser pulses. Present work goes beyond the existing paradigm of valleytronics, and opens a new realm of valley switch at PetaHertz rate.


Magnetic exchange interactions at the proximity of a superconductor. (arXiv:2306.02906v1 [cond-mat.supr-con])
Uriel Allan Aceves Rodríguez, Filipe Souza Mendes Guimarães, Sascha Brinker, Samir Lounis

Interfacing magnetism with superconductivity gives rise to a wonderful playground for intertwining key degrees of freedom: Cooper pairs, spin, charge, and spin-orbit interaction, from which emerge a wealth of exciting phenomena, fundamental in the nascent field of superconducting spinorbitronics and topological quantum technologies. Magnetic exchange interactions (MEI), being isotropic or chiral such as the Dzyaloshinskii-Moriya interactions (DMI), are vital in establishing the magnetic behavior at these interfaces as well as in dictating not only complex transport phenomena, but also the manifestation of topologically trivial or non-trivial objects as skyrmions, spirals, Yu-Shiba-Rusinov states and Majorana modes. Here, we propose a methodology enabling the extraction of the tensor of MEI from electronic structure simulations accounting for superconductivity. We apply our scheme to the case of a Mn layer deposited on Nb(110) surface and explore proximity-induced impact on the MEI. Tuning the superconducting order parameter, we unveil potential change of the magnetic order accompanied with chirality switching. Owing to its simple formulation, our methodology can be readily implemented in state-of-the-art frameworks capable of tackling superconductivity and magnetism. Our findings opens intriguing exploration paths, where chirality and magnetism can be engineered depending on the conducting nature of magneto-superconducting interfaces. We thus foresee implications in the simulations and prediction of topological superconducting bits as well as in cryogenic superconducting hybrid devices involving magnetic units.


Degenerate flat bands in twisted bilayer graphene. (arXiv:2306.02909v1 [math-ph])
Simon Becker, Tristan Humbert, Maciej Zworski

We prove that in the chiral limit of the Bistritzer-MacDonald Hamiltonian, there exist magic angles at which the Hamiltonian exhibits flat bands of multiplicity four instead of two. We analyze the structure of the Bloch functions associated with the four bands, the corresponding Chern number, and show that there exist infinitely many degenerate magic angles for a generic choice of tunnelling potentials.


Adsorption of CO and NO molecules on pristine, vacancy defected and doped graphene-like GaN monolayer: A first-principles study. (arXiv:2306.02915v1 [cond-mat.mtrl-sci])
Han-Fei Li, Si-Qi Li, Guo-Xiang Chen

In order to study the novel gas detection or sensing applications of gallium nitride monolayer (GaN-ML), we mainly focused on the structural, energetic, electronic and magnetic properties of toxic gas molecules (CO, NO) adsorbed on pristine, single vacancy (N-vacancy, Ga-vacancy) defected, and metals (Al, Fe, Pd and Pt) doped GaN-ML using density functional theory (DFT-D2 method) in this work. The calculations demonstrate that pristine GaN-ML is extremely insensitive to CO and NO together with the existence of a weak physisorption nature due to small adsorption energy, charge transfer, and long adsorption distance. It is found that both N-vacancy defected GaN-ML and Fe-doped GaN-ML can significantly increase the adsorption energy and charge transfer for CO. The CO adsorption induces the metallic characteristics of N-vacancy GaN-ML to be converted to the half-metallic characteristics together with 100% spin polarization, and it also drastically changes the magnetic moment, implying that N-vacancy GaN-ML exhibits excellent sensitivity to CO. However, Fe-doped GaN-ML is not conducive to CO detection. Moreover, N-vacancy defected and Pt-doped GaN-ML greatly improve the adsorption ability for NO compared to other substrates, and the presence of stronger orbital hybridization suggests that the interaction between them is chemisorption. Therefore, N-vacancy defected GaN-ML and Pt-doped GaN-ML can serve as potential materials in future NO sensing devices.


Boundary criticality via gauging finite subgroups: a case study on the clock model. (arXiv:2306.02976v1 [cond-mat.str-el])
Lei Su

Gauging a finite Abelian normal subgroup $\Gamma$ of a nonanomalous 0-form symmetry $G$ of a theory in $(d+1)$D spacetime can yield an unconventional critical point if the original theory has a continuous transition where $\Gamma$ is completely spontaneously broken and if $G$ is a nontrivial extension of $G/\Gamma$ by $\Gamma$. The gauged theory has symmetry $G/\Gamma \times \hat{\Gamma}^{(d-1)}$, where $\hat{\Gamma}^{(d-1)}$ is the $(d-1)$-form dual symmetry of $\Gamma$, and a 't Hooft anomaly between them. Thus it can be viewed as a boundary of a topological phase protected by $G/\Gamma \times \hat{\Gamma}^{(d-1)}$. The ordinary critical point, upon gauging, is mapped to a deconfined quantum critical point between two ordinary symmetry-breaking phases ($d =1$) or an unconventional quantum critical point between an ordinary symmetry-breaking phase and a topologically ordered phase ($d\ge 2$) associated with $G/\Gamma$ and $\hat{\Gamma}^{(d-1)}$, respectively. Order parameters and disorder parameters, before and after gauging, can be directly related. As a concrete example, we gauge the $\mathbb{z}_2$ subgroup of $\mathbb{z}_4$ symmetry of a 4-state clock model on a 1D lattice and a 2D square lattice. Since the symmetry of the clock model contains $D_8$, the dihedral group of order 8, we also analyze the anomaly structure which is similar to that in the compactified $SU(2)$ gauge theory with $\theta =\pi$ in $(3+1)$D and its mixed gauge theory. The general case is also discussed.


Stockmayer supracolloidal magnetic polymers under the influence of an applied magnetic field and a shear flow. (arXiv:2306.03005v1 [cond-mat.soft])
Ivan S. Novikau, Vladimir V. Zverev, Ekaterina V. Novak, Sofia S. Kantorovich

The idea of creating magnetically controllable colloids whose rheological properties can be finely tuned on the nano- or micro-scale has caused a lot of experimental and theoretical effort. The latter resulted in systems whose building blocks are ranging between single magnetic nanoparticles to complexes of such nanoparticles bound together by various mechanisms. The binding can be either chemical or physical, reversible or not. One way to create a system that is physically bound is to let the precrosslinked supracolloidal magnetic polymers (SMPs) to cluster due to both magnetic and Van-der-Waals-type forces. The topology of the SMPs in this case can be used to tune both magnetic and rheological properties of the resulting clusters as we show in this work. We employ Molecular Dynamics computer simulations coupled with explicit solvent modelled by Lattice-Boltzmann method in order to model the behaviour of the clusters formed by chains, rings, X- and Y-shaped SMPs in a shear flow with externally applied magnetic field. We find that the shear stabilises the shape of the clusters not letting them extend in the direction of the field and disintegrate. The clusters that show the highest response to an applied field and higher shape stability are those made of Y- and X-like SMPs.


Circular dichroism induction in WS2 by a chiral plasmonic metasurface. (arXiv:2306.03028v1 [physics.optics])
Fernando Lorén, Cyriaque Genet, Luis Martín-Moreno

We investigate the interaction between a monolayer of WS2 and a chiral plasmonic metasurface. WS2 possesses valley excitons that selectively couple with one-handed circularly polarised light. At the same time, the chiral plasmonic metasurface exhibits spin-momentum locking, leading to a robust polarisation response in the far field. Using a scattering formalism based on the coupled mode method, we analyse various optical properties of the WS2 monolayer. Specifically, we demonstrate the generation of circular dichroism in the transition metal dichalcogenide (TMD) by harnessing the excitation of surface plasmon polaritons (SPPs) in the metasurface. Moreover, we observe the emergence of other guided modes, opening up exciting possibilities for further exploration in TMD-based devices.


Light-activated memristor by Au-nanoparticle embedded HfO$_2$-bilayer/p-Si MOS device. (arXiv:2306.03044v1 [physics.app-ph])
Ankita Sengupta, Basudev Nag Chowdhury, Bodhishatwa Roy, Biswarup Satpati, Satyaban Bhunia, Sanatan Chattopadhyay

The current work proposes a novel scheme for developing a light-activated non-filamentary memristor device by fabricating an Au-nanoparticle embedded HfO$_2$-bilayer/p-Si MOS structure. Under illumination, the electrons in such embedded Au-nanoparticles are excited from d-level to quantized s-p level and are swept out on application of an appropriate gate bias, leaving behind the holes without recombination. Such photogenerated holes are confined within the nanoparticles and thus screen the external field to lead to a memristive effect in the device. The phenomenon is experimentally observed in the fabricated Pt/HfO$_2$-(layer-II)/Au-NPs/HfO$_2$-(layer-I)/p-Si devices, where such memristive effect is activated/deactivated by light pulses. The memory window and high-to-low resistance ratio of the device are obtained to be ~1 V and ~10, respectively, which suggest the performance of a standard state-of-the-art memristor. Further, the present device offers a voltage-sweep-endurance up to at least 150 cycles and the memory retention up to ~10,000 s. Such a device concept can be extended for a combination of different nanoparticles with various dimensions and dielectric layers to optimize their memristive effect for achieving CMOS-compatible memory devices with superior reliability.


Magnetic field-induced partially polarized chiral spin liquid in a transition-metal dichalcogenide Moir\'e system. (arXiv:2306.03056v1 [cond-mat.str-el])
Yixuan Huang, D. N. Sheng, Jian-Xin Zhu

As one of the most intriguing states of matter, the chiral spin liquid (CSL) has attracted much scientific interest. On one hand, its existence and mechanism in crystalline strongly correlated systems remain hotly debated. On the other hand, strong correlation driven emergent phenomena can be realized in twisted transition-metal dichalcogenide bilayers with a tremendously tunable large length scale providing a new platform for the emergence of CSLs. We focus on a strongly correlated model relevant to heterobilayer $\textrm{WSe}_{2}/\textrm{MoSe}_{2}$ and investigate the Mott insulating phase at half filling under an out-of-plane magnetic field. Considering both its orbital and spin Zeeman effects we identify three conventionally ordered phases including a $120^{\circ}$ Ne\'{e}l phase, a stripe phase and an up-up-down phase. For intermediate fields an emergent quantum spin liquid phase is identified with partial spin polarization. We further characterize the topological nature of the quantum spin liquid as the $\nu$ = 1/2 Laughlin chiral spin liquid through the topological entanglement spectrum and quantized spin pumping under spin flux insertion. In addition, we map out the quantum phase diagram for different twisted angles in an experimentally accessible parameter regime.


Strain engineering of topological magnons in chromium trihalides from first-principles. (arXiv:2104.03023v2 [cond-mat.mtrl-sci] UPDATED)
Dorye L. Esteras, José J. Baldoví

Recent experiments evidence the direct observation of spin waves in chromium trihalides and a gap at the Dirac points of the magnon dispersion in bulk CrI$_3$. However, the topological origin of this feature remains unclear and its emergence at the 2D limit has not yet been proven experimentally. Herein, we perform a fully self-consistent ab initio analysis that supports the presence of topological magnons in chromium trihalides monolayers. Our results confirm the existence of a gap around the K high-symmetry point in the linear magnon dispersion of CrI$_3$, which originates as a direct consequence of intralayer Dzyaloshinskii-Moriya (DM) interaction. In addition, our orbital resolved analysis reveals the microscopic mechanisms that can be exploited using strain engineering to increase the strength of the DM interaction and thus control the gap size in CrI$_3$. This paves the way to the further development of this family of materials as building-blocks for topological magnonics at the limit of miniaturization.


Parity flipping mediated by a quantum dot in Majorana Josephson junctions. (arXiv:2203.03671v2 [cond-mat.mes-hall] UPDATED)
Shanbo Chow, Zhi Wang, Dao-Xin Yao

The detection of the Majorana bound states (MBSs) is a central issue in the current investigation of the topological superconductors, and the topological Josephson junction is an important system for resolving this issue. In this work, we introduce an external quantum dot (QD) to Majorana Josephson junctions (MJJs), and study the parity flipping of the junction induced by the coupling between the QD and the MBSs. We demonstrate Landau-Zener (LZ) transitions between opposite Majorana parity states when the energy level of the QD is modulated. The resulted parity flipping processes exhibit voltage signals across the junction. In the presence of a periodic modulation on the QD level, we show Landau-Zener-St\"{u}ckelberg (LZS) interference on the parity states. We demonstrate distinctive interference patterns at distinct driving frequencies. These results can be used as signals for detecting the existence of the MBSs.


Gate-tunable Superconducting Diode Effect in a Three-terminal Josephson Device. (arXiv:2206.08471v4 [cond-mat.mes-hall] UPDATED)
Mohit Gupta, Gino V. Graziano, Mihir Pendharkar, Jason T. Dong, Connor P. Dempsey, Chris Palmstrøm, Vlad S. Pribiag

The phenomenon of non-reciprocal critical current in a Josephson device, termed the Josephson diode effect, has garnered much recent interest. Realization of the diode effect requires inversion symmetry breaking, typically obtained by spin-orbit interactions. Here we report observation of the Josephson diode effect in a three-terminal Josephson device based upon an InAs quantum well two-dimensional electron gas proximitized by an epitaxial aluminum superconducting layer. We demonstrate that the diode efficiency in our devices can be tuned by a small out-of-plane magnetic field or by electrostatic gating. We show that the Josephson diode effect in these devices is a consequence of the artificial realization of a current-phase relation that contains higher harmonics. We also show nonlinear DC intermodulation and simultaneous two-signal rectification, enabled by the multi-terminal nature of the devices. Furthermore, we show that the diode effect is an inherent property of multi-terminal Josephson devices, establishing an immediately scalable approach by which potential applications of the Josephson diode effect can be realized, agnostic to the underlying material platform. These Josephson devices may also serve as gate-tunable building blocks in designing topologically protected qubits.


Programmable adiabatic demagnetization for systems with trivial and topological excitations. (arXiv:2210.17256v3 [quant-ph] UPDATED)
Anne Matthies, Mark Rudner, Achim Rosch, Erez Berg

We propose a simple, robust protocol to prepare a low-energy state of an arbitrary Hamiltonian on a quantum computer or programmable quantum simulator. The protocol is inspired by the adiabatic demagnetization technique, used to cool solid-state systems to extremely low temperatures. A fraction of the qubits (or spins) is used to model a spin bath that is coupled to the system. By an adiabatic ramp down of a simulated Zeeman field acting on the bath spins, energy and entropy are extracted from the system. The bath spins are then measured and reset to the polarized state, and the process is repeated until convergence to a low-energy steady state is achieved. We demonstrate the protocol via application to the quantum Ising model. We study the protocol's performance in the presence of noise and show how the information from the measurement of the bath spins can be used to monitor the cooling process. The performance of the algorithm depends on the nature of the excitations of the system; systems with non-local (topological) excitations are more difficult to cool than those with local excitations. We explore the possible mitigation of this problem by trapping topological excitations.


Thermal conductance and noise of Majorana modes along interfaced $\nu=5/2$ fractional quantum Hall states. (arXiv:2211.08000v2 [cond-mat.mes-hall] UPDATED)
Michael Hein, Christian Spånslätt

We study transport along interfaced edge segments of fractional quantum Hall states hosting non-Abelian Majorana modes. With an incoherent model approach, we compute, for edge segments based on Pfaffian, anti-Pfaffian, and particle-hole-Pfaffian topological orders, thermal conductances, voltage biased noise, and delta-$T$ noise. We determine how the thermal equilibration of edge modes impacts these observables and identify the temperature scalings of transitions between regimes of differently quantized thermal conductances. In combination with recent experimental data, we use our results to estimate thermal and charge equilibration lengths in real devices. We also propose an experimental setup which permits measuring several transport observables for interfaced fractional quantum Hall edges in a single device. It can, e.g., be used to rule out edge reconstruction effects. In this context, we further point out some subtleties in two-terminal thermal conductance measurements and how to remedy them. Our findings are consistent with recent experimental results pointing towards a particle-hole-Pfaffian topological order at filling $\nu=5/2$ in GaAs/AlGaAs, and provide further means to pin-point the edge structure at this filling and possibly also other exotic fractional quantum Hall states.


Heat transport in Weyl semimetals in the hydrodynamic regime. (arXiv:2211.09254v2 [cond-mat.mes-hall] UPDATED)
Yonatan Messica, Pavel M. Ostrovsky, Dmitri B. Gutman

We study heat transport in a Weyl semimetal with broken time-reversal symmetry in the hydrodynamic regime. At the neutrality point, the longitudinal heat conductivity is governed by the momentum relaxation (elastic) time, while longitudinal electric conductivity is controlled by the inelastic scattering time. In the hydrodynamic regime this leads to a large longitudinal Lorenz ratio. As the chemical potential is tuned away from the neutrality point, the longitudinal Lorenz ratio decreases because of suppression of the heat conductivity by the Seebeck effect. The Seebeck effect (thermopower) and the open circuit heat conductivity are intertwined with the electric conductivity. The magnitude of Seebeck tensor is parametrically enhanced, compared to the non-interacting model, in a wide parameter range. While the longitudinal component of Seebeck response decreases with increasing electric anomalous Hall conductivity $\sigma_{xy}$, the transverse component depends on $\sigma_{xy}$ in a non-monotonous way. Via its effect on the Seebeck response, large $\sigma_{xy}$ enhances the longitudinal Lorenz ratio at a finite chemical potential. At the neutrality point, the transverse heat conductivity is determined by the Wiedemann-Franz law. Increasing the distance from the neutrality point, the transverse heat conductivity is enhanced by the transverse Seebeck effect and follows its non-monotonous dependence on $\sigma_{xy}$.


Appearance of Odd-Frequency Superconductivity in a Relativistic Scenario. (arXiv:2212.01849v2 [cond-mat.supr-con] UPDATED)
Patrick J. Wong, Alexander V. Balatsky

Odd-frequency superconductivity is an exotic superconducting state in which the symmetry of the gap function is odd in frequency. Here we show that an inherent odd-frequency mode emerges dynamically under application of a Lorentz transformation of the anomalous Green function with the general frequency-dependent gap function. To see this, we consider a Dirac model with quartic potential and perform a mean-field analysis to obtain a relativistic Bogoliubov-de Gennes system. Solving the resulting Gor'kov equations yields expressions for relativistic normal and anomalous Green functions. The form of the relativistically invariant pairing term is chosen such that it reduces to BCS form in the non-relativistic limit. We choose an ansatz for the gap function in a particular frame which is even-frequency and analyze the effects on the anomalous Green function under a boost into a relativistic frame. The odd-frequency pairing emerges dynamically as a result of the boost. In the boosted frame the order parameter contains terms which are both even and odd in frequency. The relativistic correction to the anomalous Green function to first order in the boost parameter is completely odd in frequency. This work provides evidence that odd-frequency pairing may form intrinsically within relativistic superconductors.


Full Classification of Transport on an Equilibrated 5/2 Edge via Shot Noise. (arXiv:2212.05732v2 [cond-mat.mes-hall] UPDATED)
Sourav Manna, Ankur Das, Moshe Goldstein, Yuval Gefen

The nature of the bulk topological order of the 5/2 non-Abelian fractional quantum Hall state and the steady-state of its edge are long-studied questions. The most promising non-Abelian model bulk states are the Pfaffian (Pf), anti-Pffafian (APf), and particle-hole symmetric Pfaffian (PHPf). Here, we propose to employ a set of dc current-current correlations \emph{(electrical shot noise)} in order to distinguish among the Pf, APf, and PHPf candidate states, as well as to determine their edge thermal equilibration regimes: full vs. partial. Using other tools, measurements of GaAs platforms have already indicated consistency with the PHPf state. Our protocol, realizable with available experimental tools, is based on fully electrical measurements.


Achiral dielectric metasurfaces for spectral and polarization control of valley specific light emission from monolayer MoS2. (arXiv:2212.09147v2 [physics.optics] UPDATED)
Yin Liu, Sze Cheung Lau, Wen-Hui Sophia Cheng, Amalya Johnson, Qitong Li, Emma Simmerman, Ouri Karni, Jack Hu, Fang Liu, Mark L. Brongersma, Tony F. Heinz, Jennifer A. Dionne

Excitons in two-dimensional transition metal dichalcogenides have a valley degree of freedom that can be optically accessed and manipulated for quantum information processing. Here, we integrate MoS2 with achiral silicon disk array metasurfaces to enhance and control valley-specific absorption and emission. Through the coupling to the metasurface Mie modes, the intensity and lifetime of the emission of neutral excitons, trions and defect bound excitons can be enhanced, while the spectral shape can be modified. Additionally, we demonstrate the symmetric enhancement of the degree-of-polarization (DOP) of neutral exciton and trions via valley-resolved PL measurements, and find that the DOP can be as high as 24% for exciton emission and 34% for trion emission at 100K. These results can be understood by analyzing the near-field impact of metasurface resonators on both the chiral absorption of MoS2 emitters as well as the enhanced emission from the Purcell effect. Combining Si-compatible photonic design with large-scale (mm-scale) 2D materials integration, our work makes an important step towards on-chip valleytronic applications approaching room-temperature operation.


Composing parafermions: a construction of $Z_{N}$ fractional quantum Hall systems and a modern understanding of confinement and duality. (arXiv:2212.12999v2 [cond-mat.str-el] UPDATED)
Yoshiki Fukusumi

In this work, we propose a modern view of the integer spin simple currents which have played a central role in discrete torsion. We reintroduce them as nonanomalous composite particles constructed from $Z_{N}$ parafermionic field theories. These composite particles have an analogy with the Cooper pair in the Bardeen-Cooper-Schrieffer theory and can be interpreted as a typical example of anyon condensation. Based on these $Z_{N}$ anomaly free composite particles, we propose a systematic construction of the cylinder partition function of $Z_{N}$ fractional quantum Hall effects (FQHEs). One can expect realizations of a class of general topological ordered systems by breaking the bulk-edge correspondence of the bosonic parts of these FQH models. We also give a brief overview of various phenomena in contemporary condensed matter physics, such as $SU(N)$ Haldane conjecture, general gapless and gapped topological order with respect to the quantum anomaly defined by charges of these simple currents and bulk and boundary renormalization group flow. Moreover, we point out an analogy between these FQHEs and 2d quantum gravities coupled to matter, and propose a $Z_{N}$ generalization of supersymmetry known as "fractional supersymmetry" in the composite parafermionic theory and study its analogy with quark confinement. Our analysis gives a simple but general understanding of the contemporary physics of topological phases in the form of the partition functions derived from the operator formalism.


Topological Quantum Dimers Emerging from Kitaev Spin Liquid Bilayer: Anyon Condensation Transition. (arXiv:2301.05721v2 [cond-mat.str-el] UPDATED)
Kyusung Hwang

We present a bilayer spin model that illuminates the mechanism of topological anyon condensation transition. Our model harbors two distinct topological phases, Kitaev spin liquid bilayer state and resonating valence bond (RVB) state connected by a continuous transition. We show that the transition occurs by anyon condensation, and the hardcore dimer constraint of the RVB state plays a role of the order parameter. This model study offers an intuitive picture for anyon condensation transition, and is broadly applicable to generic tri-coordinated lattices preserving the emergence of the RVB state from the Kitaev bilayer.


Holographic entanglement renormalisation for fermionic quantum matter: geometrical and topological aspects. (arXiv:2302.10590v2 [cond-mat.str-el] UPDATED)
Abhirup Mukherjee, Siddhartha Patra, Siddhartha Lal

On performing a sequence of renormalisation group (RG) transformations on a system of two-dimensional non-interacting Dirac fermions placed on a torus, we demonstrate the emergence of an additional spatial dimension arising out of the scaling of multipartite entanglement. The renormalisation of entanglement under this flow exhibits a hierarchy across scales as well as number of parties. Geometric measures defined in this emergent space, such as distances and curvature, can be related to the RG beta function of the coupling $g$ responsible for the spectral gap. This establishes a holographic connection between the spatial geometry of the emergent space in the bulk and the entanglement properties of the quantum theory lying on its boundary. Depending on the anomalous dimension of the coupling $g$, three classes of spaces (bounded, unbounded and flat) are generated from the RG. We show that changing from one class to another involves a topological transition. By minimising the central charge of the conformal field theory describing the noninteracting electrons under the RG flow, the RG transformations are shown to satisfy the $c-$theorem of Zamolodchikov. This is shown to possess a dual within the emergent geometric space, in the form of a convergence parameter that is minimised at large distances. In the presence of an Aharonov-Bohm flux, the entanglement gains a geometry-independent piece which is shown to be topological, sensitive to changes in boundary conditions, and can be related to the Luttinger volume of the system of electrons. In the presence of a strong transverse magnetic field, the system becomes insulating and Luttinger's theorem does not hold. We show instead that the entanglement contains a term that can be related to the Chern numbers of the quantum Hall states. This yields a relation between the topological invariants of the metallic and the quantum Hall systems.


Degenerate Topological Edge States in Multimer Chains. (arXiv:2303.00053v2 [cond-mat.mes-hall] UPDATED)
Jun Li, Yaping Yang, C.M. Hu

We propose and experimentally realize a class of quasi-one-dimensional topological lattices whose unit cells are constructed by coupled multiple identical resonators, with uniform hopping and inversion symmetry. In the presence of path-induced effective zero hopping within the unit cells, the systems are characterized by complete multimerization with degenerate $-1$ energy edge states for open boundary condition. Su-Schrieffer-Heeger subspaces with fully dimerized limits corresponding to pairs of nontrivial flat bands are derived from the Hilbert spaces. In particular, topological bound states in the continuum (BICs) are inherently present in even multimer chains, manifested by embedding the topological bound states into a continuous band assured by bulk-boundary correspondence. Moreover, we experimentally demonstrate the degenerate topological edge states and topological BICs in inductor-capacitor circuits.


Strain Engineering of Photo-induced Topological Phases in 2D Ferromagnets. (arXiv:2303.03305v3 [cond-mat.mes-hall] UPDATED)
T. V. C. Antão, N. M. R. Peres

We argue that strain engineering is a powerful tool which may facilitate the experimental realization and control of topological phases in laser-driven 2D ferromagnetic systems. To this extent, we show that by applying a circularly polarized laser field to a 2D honeycomb ferromagnet which is uniaxially strained in either the zig-zag or armchair direction, it is possible to generate a synthetic Dzyaloshinskii-Moriya interaction (DMI) tunable by the intensity of the applied electric field, as well as by the magnitude of applied strain. Such deformations enable transitions to phases with opposite sign of Chern number, or to trivial phases. These are basic results that could pave the way for the development of a new field of Strain Engineered Topological Spintronics (SETS).


Extracting quantum-geometric effects from Ginzburg-Landau theory in a multiband Hubbard model. (arXiv:2304.03613v3 [cond-mat.supr-con] UPDATED)
M. Iskin

We first apply functional-integral approach to a multiband Hubbard model near the critical pairing temperature, and derive a generic effective action that is quartic in the fluctuations of the pairing order parameter. Then we consider time-reversal-symmetric systems with uniform (i.e., at both low-momentum and low-frequency) pairing fluctuations in a unit cell, and derive the corresponding time-dependent Ginzburg-Landau (TDGL) equation. In addition to the conventional intraband contribution that depends on the derivatives of the Bloch bands, we show that the kinetic coefficients of the TDGL equation have a geometric contribution that is controlled by both the quantum-metric tensor of the underlying Bloch states and their band-resolved quantum-metric tensors. Furthermore we show that thermodynamic properties such as London penetration depth, GL coherence length, GL parameter and upper critical magnetic field have an explicit dependence on quantum geometry.


Thermoelectric properties of the Corbino disk in graphene. (arXiv:2304.03827v3 [cond-mat.mes-hall] UPDATED)
Adam Rycerz, Katarzyna Rycerz, Piotr Witkowski

Thermopower and the Lorentz number for an edge-free (Corbino) graphene disk in the quantum Hall regime is calculated within the Landauer-B\"{u}ttiker formalism. We find, by varying the electrochemical potential, that amplitude of the Seebeck coefficient follows a modified Goldsmid-Sharp relation, in which energy gap is identified with the interval between zero-th and first Landau level in bulk graphene. Analogous relation for the Lorentz number is also determined. Therefore, these thermoelectric properties are solely defined by the magnetic field, temperature, the Fermi velocity in graphene, and fundamental constants including the electrons charge, the Planck and Boltzmann constants, being independent on the system geometric dimensions. This suggests that the Corbino disk in graphene may operate as a thermoelectric thermometer, allowing to determine small temperature difference between two reservoirs, if mean temperature and magnetic field are known.


Exploring the interfacial coupling between graphene and the antiferromagnetic insulator MnPSe$_3$. (arXiv:2304.05757v2 [cond-mat.mtrl-sci] UPDATED)
Xin Yi, Qiao Chen, Kexin Wang, Yuanyang Yu, Yi Yan, Xin Jiang, Chengyu Yan, Shun Wang

Interfacial coupling between graphene and other 2D materials can give rise to intriguing physical phenomena. In particular, several theoretical studies predict that the interplay between graphene and an antiferromagnetic insulator could lead to the emergence of quantum anomalous Hall phases. However, such phases have not been observed experimentally yet, and further experimental studies are needed to reveal the interaction between graphene and antiferromagnetic insulators. Here, we report the study in heterostructures composed of graphene and the antiferromagnetic insulator MnPSe$_3$. It is found that the MnPSe$_3$ has little impact on the quantum Hall phases apart from doping graphene via interfacial charge transfer. However, the magnetic order can contribute indirectly via process like Kondo effect, as evidenced by the observed minimum in the temperature-resistance curve between 20-40 K, far below the N\'eel temperature (70 K).


A Multi-Purpose Platform for Analog Quantum Simulation. (arXiv:2304.08433v2 [cond-mat.quant-gas] UPDATED)
Shuwei Jin, Kunlun Dai, Joris Verstraten, Maxime Dixmerias, Ragheed Alhyder, Christophe Salomon, Bruno Peaudecerf, Tim de Jongh, Tarik Yefsah

Atom-based quantum simulators have had tremendous success in tackling challenging quantum many-body problems, owing to the precise and dynamical control that they provide over the systems' parameters. They are, however, often optimized to address a specific type of problems. Here, we present the design and implementation of a $^6$Li-based quantum gas platform that provides wide-ranging capabilities and is able to address a variety of quantum many-body problems. Our two-chamber architecture relies on a robust and easy-to-implement combination of gray molasses and optical transport from a laser-cooling chamber to a glass cell with excellent optical access. There, we first create unitary Fermi superfluids in a three-dimensional axially symmetric harmonic trap and characterize them using in situ thermometry, reaching temperatures below 20 nK. This allows us to enter the deep superfluid regime with samples of extreme diluteness, where the interparticle spacing is sufficiently large for direct single-atom imaging. Secondly, we generate optical lattice potentials with triangular and honeycomb geometry in which we study diffraction of molecular Bose-Einstein condensates, and show how going beyond the Kapitza-Dirac regime allows us to unambiguously distinguish between the two geometries. With the ability to probe quantum many-body physics in both discrete and continuous space, and its suitability for bulk and single-atom imaging, our setup represents an important step towards achieving a wide-scope quantum simulator.


Asymmetries in triboelectric charging: generalizing mosaic models to different-material samples and sliding contacts. (arXiv:2304.12861v2 [cond-mat.soft] UPDATED)
Galien Grosjean, Scott Waitukaitis

Nominally identical materials exchange net electric charge during contact through a mechanism that is still debated. `Mosaic models', in which surfaces are presumed to consist of a random patchwork of microscopic donor/acceptor sites, offer an appealing explanation for this phenomenon. However, recent experiments have shown that global differences persist even between same-material samples, which the standard mosaic framework does not account for. Here, we expand the mosaic framework by incorporating global differences in the densities of donor/acceptor sites. We develop an analytical model, backed by numerical simulations, that smoothly connects the global and deterministic charge transfer of different materials to the local and stochastic mosaic picture normally associated with identical materials. Going further, we extend our model to explain the effect of contact asymmetries during sliding, providing a plausible explanation for reversal of charging sign that has been observed experimentally.


A Chern-Simons theory for dipole symmetry. (arXiv:2305.02492v2 [cond-mat.str-el] UPDATED)
Xiaoyang Huang

We present effective field theories for dipole symmetric topological matters that can be described by the Chern-Simons theory. Unlike most studies using higher-rank gauge theory, we develop a framework with both U(1) and dipole gauge fields. As a result, only the highest multipole symmetry can support the 't Hooft anomaly. We show that with appropriate point group symmetries, the dipolar Chern-Simons theory can exist in any dimension and, moreover, the bulk-edge correspondence can depend on the boundary. As two applications, we draw an analogy between the dipole anomaly and the torsional anomaly and generalize particle-vortex duality to dipole phase transitions. All of the above are in the flat spacetime limit, but our framework is able to systematically couple dipole symmetry to curved spacetime. Based on that, we give a proposal about anomalous dipole hydrodynamics. Moreover, we show that the fracton-elasticity duality arises naturally from a non-abelian Chern-Simons theory in 3D.


Extended application of random-walk shielding-potential viscosity model of metals in wide temperature region. (arXiv:2305.16551v2 [cond-mat.stat-mech] UPDATED)
Yuqing Cheng, Xingyu Gao, Qiong Li, Yu Liu, Haifeng Song, Haifeng Liu

The transport properties of matter have been widely investigated. In particular, shear viscosity over a wide parameter space is crucial for various applications, such as designing inertial confinement fusion (ICF) targets and determining the Rayleigh-Taylor instability. In this work, an extended random-walk shielding-potential viscosity model (RWSP-VM) [Phys. Rev. E 106, 014142] based on the statistics of random-walk ions and the Debye shielding effect is proposed to elevate the temperature limit of RWSP-VM in evaluating the shear viscosity of metals. In the extended model, we reconsider the collision diameter that is introduced by hard-sphere concept, hence, it is applicable in both warm and hot temperature regions (10^1-10^7 eV) rather than the warm temperature region (10^1-10^2 eV) in which RWSP-VM is applicable. The results of Be, Al, Fe, and U show that the extended model provides a systematic way to calculate the shear viscosity of arbitrary metals at the densities from about 0.1 to 10 times the normal density (the density at room temperature and 1 standard atmosphere). This work will help to develop viscosity model in wide region when combined with our previous low temperature viscosity model [AIP Adv. 11, 015043].


Found 12 papers in prb
Date of feed: Tue, 06 Jun 2023 03:17:14 GMT

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Structure of the normal state and origin of the Schottky anomaly in the correlated heavy-fermion superconductor $\mathrm{U}{\mathrm{Te}}_{2}$
S. Khmelevskyi, L. V. Pourovskii, and E. A. Tereshina-Chitrova
Author(s): S. Khmelevskyi, L. V. Pourovskii, and E. A. Tereshina-Chitrova

The recently discovered $\mathrm{U}{\mathrm{Te}}_{2}$ superconductor is regarded as a heavy-fermion mixed-valence system with very peculiar properties within the normal and superconducting (SC) states. It shows no signs of magnetic order, but has a strong anisotropy of magnetic susceptibility and SC…


[Phys. Rev. B 107, 214501] Published Mon Jun 05, 2023

Topological field-effect transistor with quantized on/off conductance of helical/chiral dislocation states
Xiaoyin Li and Feng Liu
Author(s): Xiaoyin Li and Feng Liu

Topology is a key ingredient driving the emergence of quantum devices. The topological field-effect transistor (TFET) has been proposed to outperform the conventional field-effect transistor by replacing the on state with topology-protected quantized conductance, while the off state has the same nor…


[Phys. Rev. B 107, 224101] Published Mon Jun 05, 2023

Discrete Laplacian thermostat for spin systems with conserved dynamics
Andrea Cavagna, Javier Cristín, Irene Giardina, and Mario Veca
Author(s): Andrea Cavagna, Javier Cristín, Irene Giardina, and Mario Veca

A well-established numerical technique to study the dynamics of spin systems in which symmetries and conservation laws play an important role is to microcanonically integrate their reversible equations of motion, obtaining thermalization through initial conditions drawn with the canonical distributi…


[Phys. Rev. B 107, 224302] Published Mon Jun 05, 2023

Defect bulk-boundary correspondence of topological skyrmion phases of matter
Shu-Wei Liu, Li-kun Shi, and Ashley M. Cook
Author(s): Shu-Wei Liu, Li-kun Shi, and Ashley M. Cook

Unpaired Majorana zero modes are central to topological quantum computation schemes as building blocks of topological qubits, and are therefore under intense experimental and theoretical investigation. Their generalizations to parafermions and Fibonacci anyons are also of great interest, in particul…


[Phys. Rev. B 107, 235109] Published Mon Jun 05, 2023

Prediction of non-Abelian fractional quantum Hall effect at $ν=2+\frac{4}{11}$
Koyena Bose and Ajit C. Balram
Author(s): Koyena Bose and Ajit C. Balram

The fractional quantum Hall effect (FQHE) in the second Landau level (SLL) likely stabilizes non-Abelian topological orders. Recently, a parton sequence has been proposed to capture many of the fractions observed in the SLL [A. C. Balram, SciPost Phys. 10, 083 (2021)]. We consider the first member o…


[Phys. Rev. B 107, 235111] Published Mon Jun 05, 2023

Hall effect of ferro/antiferromagnetic wallpaper fermions
Koki Mizuno and Ai Yamakage
Author(s): Koki Mizuno and Ai Yamakage

Nonsymmorphic crystals can host characteristic double surface Dirac cones with fourfold degeneracy on the Dirac points, called wallpaper fermion, protected by wallpaper group symmetry. We clarify the charge and spin Hall effect of wallpaper fermions in the presence of the (anti)ferromagnetism. Based…


[Phys. Rev. B 107, 235301] Published Mon Jun 05, 2023

Corbino magnetoresistance in neutral graphene
Vanessa Gall, Boris N. Narozhny, and Igor V. Gornyi
Author(s): Vanessa Gall, Boris N. Narozhny, and Igor V. Gornyi

We explore the magnetohydrodynamics of Dirac fermions in neutral graphene in the Corbino geometry. Based on the fully consistent hydrodynamic description derived from a microscopic framework and taking into account all peculiarities of graphene-specific hydrodynamics, we report the results of a comp…


[Phys. Rev. B 107, 235401] Published Mon Jun 05, 2023

Second-order topology and supersymmetry in two-dimensional topological insulators
Clara S. Weber, Mikhail Pletyukhov, Zhe Hou, Dante M. Kennes, Jelena Klinovaja, Daniel Loss, and Herbert Schoeller
Author(s): Clara S. Weber, Mikhail Pletyukhov, Zhe Hou, Dante M. Kennes, Jelena Klinovaja, Daniel Loss, and Herbert Schoeller

We unravel a fundamental connection between supersymmetry (SUSY) and a wide class of two-dimensional (2D) second-order topological insulators (SOTI). This particular supersymmetry is induced by applying a half-integer Aharonov-Bohm flux $f=\mathrm{Φ}/{\mathrm{Φ}}_{0}=1/2$ through a hole in the syste…


[Phys. Rev. B 107, 235402] Published Mon Jun 05, 2023

Hall conductivity as the topological invariant in magnetic Brillouin zone in the presence of interactions
M. Selch, M. Suleymanov, M. A. Zubkov, and C. X. Zhang
Author(s): M. Selch, M. Suleymanov, M. A. Zubkov, and C. X. Zhang

Hall conductivity for the intrinsic anomalous quantum Hall effect in homogeneous systems is given by the topological invariant composed of the Green function depending on momentum of quasiparticle. This expression reveals correspondence with the mathematical notion of the degree of mapping. A more i…


[Phys. Rev. B 107, 245105] Published Mon Jun 05, 2023

Quantum Monte Carlo study of superconductivity in rhombohedral trilayer graphene under an electric field
Huijia Dai, Runyu Ma, Xiao Zhang, Ting Guo, and Tianxing Ma
Author(s): Huijia Dai, Runyu Ma, Xiao Zhang, Ting Guo, and Tianxing Ma

By using the constrained-phase quantum Monte Carlo method, we performed a systematic study of the ground state of the half filled Hubbard model for a trilayer honeycomb lattice. We analyze the effect of the perpendicular electric field on the electronic structure, magnetic property, and pairing corr…


[Phys. Rev. B 107, 245106] Published Mon Jun 05, 2023

Topological invariant for multiband non-Hermitian systems with chiral symmetry
Chun-Chi Liu, Liu-Hao Li, and Jin An
Author(s): Chun-Chi Liu, Liu-Hao Li, and Jin An

Topology plays an important role in non-Hermitian systems. How to characterize a non-Hermitian topological system under open-boundary conditions (OBCs) is a challenging problem. A one-dimensional (1D) topological invariant defined on a generalized Brillion zone (GBZ) was recently found to successful…


[Phys. Rev. B 107, 245107] Published Mon Jun 05, 2023

Waiting time distributions in quantum spin Hall based heterostructures
F. Schulz, D. Chevallier, and M. Albert
Author(s): F. Schulz, D. Chevallier, and M. Albert

We study the scattering processes and the associated waiting time distributions (WTDs) in heterostructures based on one-dimensional helical edge states of a two-dimensional topological insulator. In combination with a proximitized $s$-wave superconductor and an applied magnetic field a topological t…


[Phys. Rev. B 107, 245406] Published Mon Jun 05, 2023

Found 2 papers in pr_res
Date of feed: Tue, 06 Jun 2023 03:17:13 GMT

Search terms: (topolog[a-z]+)|(graphit[a-z]+)|(rhombohedr[a-z]+)|(graphe[a-z]+)|(chalcog[a-z]+)|(landau)|(weyl)|(dirac)|(STM)|(scan[a-z]+ tunne[a-z]+ micr[a-z]+)|(scan[a-z]+ tunne[a-z]+ spectr[a-z]+)|(scan[a-z]+ prob[a-z]+ micr[a-z]+)|(MoS.+\d+|MoS\d+)|(MoSe.+\d+|MoSe\d+)|(MoTe.+\d+|MoTe\d+)|(WS.+\d+|WS\d+)|(WSe.+\d+|WSe\d+)|(WTe.+\d+|WTe\d+)|(Bi\d+Rh\d+I\d+|Bi.+\d+.+Rh.+\d+.+I.+\d+.+)|(BiTeI)|(BiTeBr)|(BiTeCl)|(ZrTe5|ZrTe.+5)|(Pt2HgSe3|Pt.+2HgSe.+3)|(jacuting[a-z]+)

Kagome chiral spin liquid in transition metal dichalcogenide moiré bilayers
Johannes Motruk, Dario Rossi, Dmitry A. Abanin, and Louk Rademaker
Author(s): Johannes Motruk, Dario Rossi, Dmitry A. Abanin, and Louk Rademaker

An experimental realization of the Heisenberg model on the kagome lattice is proposed in highly tunable moiré bilayers of transition metal dichalcogenides. It is demonstrated that the system can host a topologically ordered chiral spin liquid and the much-studied kagome spin liquid for realistic material parameters.


[Phys. Rev. Research 5, L022049] Published Mon Jun 05, 2023

Experimental characterization of three-band braid relations in non-Hermitian acoustic lattices
Qicheng Zhang, Luekai Zhao, Xun Liu, Xiling Feng, Liwei Xiong, Wenquan Wu, and Chunyin Qiu
Author(s): Qicheng Zhang, Luekai Zhao, Xun Liu, Xiling Feng, Liwei Xiong, Wenquan Wu, and Chunyin Qiu

Braids are ubiquitous in mathematics and physics. The interesting multistrand braiding topology is visualized by a concise acoustic setup. From the measurements of both eigenvalues and eigenstates, a noncommutative braid relation and a swappable braid relation is precisely captured.


[Phys. Rev. Research 5, L022050] Published Mon Jun 05, 2023

Found 3 papers in nat-comm


Search terms: (topolog[a-z]+)|(graphit[a-z]+)|(rhombohedr[a-z]+)|(graphe[a-z]+)|(chalcog[a-z]+)|(landau)|(weyl)|(dirac)|(STM)|(scan[a-z]+ tunne[a-z]+ micr[a-z]+)|(scan[a-z]+ tunne[a-z]+ spectr[a-z]+)|(scan[a-z]+ prob[a-z]+ micr[a-z]+)|(MoS.+\d+|MoS\d+)|(MoSe.+\d+|MoSe\d+)|(MoTe.+\d+|MoTe\d+)|(WS.+\d+|WS\d+)|(WSe.+\d+|WSe\d+)|(WTe.+\d+|WTe\d+)|(Bi\d+Rh\d+I\d+|Bi.+\d+.+Rh.+\d+.+I.+\d+.+)|(BiTeI)|(BiTeBr)|(BiTeCl)|(ZrTe5|ZrTe.+5)|(Pt2HgSe3|Pt.+2HgSe.+3)|(jacuting[a-z]+)

Lanthanide-doped MoS2 with enhanced oxygen reduction activity and biperiodic chemical trends
< author missing >

Observation of bulk quadrupole in topological heat transport
< author missing >

Parallel interrogation of the chalcogenide-based micro-ring sensor array for photoacoustic tomography
< author missing >