Found 31 papers in cond-mat
Date of feed: Fri, 06 Oct 2023 00:30:00 GMT

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Comment on "Anomalous Reentrant 5/2 Quantum Hall Phase at Moderate Landau-Level-Mixing Strength''. (arXiv:2310.03041v1 [cond-mat.mes-hall])
Steven H. Simon

Das, Das, and Mandal (PRL 131, 056202, 2023) examine a wavefunction for nu = 5/2 on a sphere including moderate Landau-Level mixing evaluated perturbatively. The wavefunction they find is not a fractional quantum Hall (FQH) state as claimed, but rather shows phase separation or bubble/stripe formation.

Entanglement entropy scaling in critical phases of 1D quasiperiodic systems. (arXiv:2310.03060v1 [cond-mat.str-el])
Miguel Gonçalves

We study the scaling of the entanglement entropy in different classes of one-dimensional fermionic quasiperiodic systems with and without pairing, focusing on multifractal critical points/phases. We find that the entanglement entropy scales logarithmically with the subsystem size $N_{A}$ with a proportionality coefficient $\mathcal{C}$, as in homogeneous critical points, apart from possible additional small oscillations. In the absence of pairing, we find that the entanglement entropy coefficient $\mathcal{C}$ is non-universal and depends significantly and non-trivially both on the model parameters and electron filling, in multifractal critical points. In some of these points, $\mathcal{C}$ can take values close to the homogeneous (or ballistic) system, although it typically takes smaller values. We find a close relation between the behaviour of the entanglement entropy and the small-$q$ (long-wavelength) dependence of the momentum structure factor $\mathcal{S}(q)$. $\mathcal{S}(q)$ increases linearly with q as in the homogeneous case, with a slope that grows with $\mathcal{C}$. In the presence of pairing, we find that even the addition of small anomalous terms affects very significantly the scaling of the entanglement entropy compared to the unpaired case. In particular, we focused on topological phase transitions for which the gap closes with either extended or critical multifractal states. In the former case, the scaling of the entanglement entropy mirrors the behaviour observed at the critical points of the homogeneous Kitaev chain, while in the latter, it shows only slight deviations arising at small length scales. In contrast with the unpaired case, we always observe $\mathcal{C}\approx1/6$ for different critical points, the known value for the homogeneous Kitaev chain with periodic boundary conditions.

Group-theoretic error mitigation enabled by classical shadows and symmetries. (arXiv:2310.03071v1 [quant-ph])
Andrew Zhao, Akimasa Miyake

Estimating expectation values is a key subroutine in many quantum algorithms. However, near-term implementations face two major challenges: a limited number of samples to learn a large collection of observables, and the accumulation of errors in devices without quantum error correction. To address these challenges simultaneously, we develop a quantum error-mitigation strategy which unifies the group-theoretic structure of classical-shadow tomography with symmetries in quantum systems of interest. We refer to our protocol as "symmetry-adjusted classical shadows," as it mitigates errors by adjusting estimators according to how known symmetries are corrupted under those errors. As a concrete example, we highlight global $\mathrm{U}(1)$ symmetry, which manifests in fermions as particle number and in spins as total magnetization, and illustrate their unification with respective classical-shadow protocols. One of our main results establishes rigorous error and sampling bounds under readout errors obeying minimal assumptions. Furthermore, to probe mitigation capabilities against a more comprehensive class of gate-level errors, we perform numerical experiments with a noise model derived from existing quantum processors. Our analytical and numerical results reveal symmetry-adjusted classical shadows as a flexible and low-cost strategy to mitigate errors from noisy quantum experiments in the ubiquitous presence of symmetry.

Theoretical prediction of giant Hall high harmonic generation in monolayer NbSe$_2$. (arXiv:2310.03080v1 [cond-mat.mtrl-sci])
Daniel A. Rehn, Towfiq Ahmed, Jinkyoung Yoo, Rohit Prasankumar, Jian-Xin Zhu

High harmonic generation (HHG) is a powerful probe of electron dynamics on attosecond to femtosecond timescales and has been successfully used to detect electronic and structural changes in novel solid-state quantum materials, including transition metal dichalcogenides (TMDs). Among TMDs, bulk NbSe$_2$ exhibits charge density wave (CDW) order below 33 K and becomes superconducting below 7.3 K. Monolayer NbSe$_2$ is therefore interesting as a material whose different structural and electronic properties could be probed via HHG. Here, we predict the HHG response of the pristine 2H and CDW phases of monolayer NbSe$_2$ using real-time time-dependent density functional theory under the application of a simulated laser pulse excitation. We find that due to the lack of inversion symmetry in both monolayer phases, it is possible to excite even harmonics and that, importantly, the even harmonics appear strictly as the transverse (Hall) components of the current response under excitations polarized along the zigzag direction of the monolayer, while odd harmonics arise from the longitudinal current response in all excitation directions. This suggests that the even and odd harmonic response can be controlled via the polarization of the probing field, opening a new avenue for potentially useful applications in opto-electronic devices.

Exceeding the Chandrasekhar-Clogston limit in flat-band superconductors: A multiband strong-coupling approach. (arXiv:2310.03082v1 [cond-mat.supr-con])
Kristian Mæland, Asle Sudbø

Hybrid systems of superconductors and magnets display several intriguing properties, both from a fundamental physics point of view and with practical applications. Promising applications in superconducting spintronics motivate a search for systems where superconductivity can survive larger inplane critical magnetic fields than the conventional limit. The Chandrasekhar-Clogston (CC) limit applies to thin-film conventional superconductors with inplane magnetic fields such that orbital effects may be ignored. For a magnetic field strength comparable to the superconducting gap at zero temperature and zero field, a spin-split normal state attains lower free energy than the superconducting state. A multiband superconductor with a flat band placed just below the Fermi surface has been shown to surpass the CC limit using weak-coupling theory. Since the dimensionless coupling determining the critical temperature scales with the density of states, it is natural to anticipate corrections from strong-coupling theory in flat-band systems, owing to the large density of states of the flat bands. We derive Eliashberg equations and the free energy for a multiband superconductor in a magnetic field. First, we show that the CC limit can be exceeded by a small amount in one-band strong-coupling superconductors due to self-energy renormalization of the magnetic field. Next, we consider a two-band system with one flat band and find that the CC limit can be exceeded by a large amount also in strong-coupling theory, even when including hybridization between bands that intersect.

Tunneling of fluxons via a Josephson resonant level. (arXiv:2310.03102v1 [cond-mat.mes-hall])
T. Vakhtel, P. D. Kurilovich, M. Pita-Vidal, A. Bargerbos, V. Fatemi, B. van Heck

Fluxons in a superconducting loop can be coherently coupled by quantum phase slips occurring at a weak link such as a Josephson junction. If Cooper pair tunneling at the junction occurs through a resonant level, $2\pi$ quantum phase slips are suppressed, and fluxons are predominantly coupled by $4\pi$ quantum phase slips. We analyze this scenario by computing the coupling between fluxons as the level is brought into resonance with the superconducting condensate. The results indicate that the $4\pi$-dominated regime can be observed directly in the transition spectrum for circuit parameters typical of a fluxonium qubit. We also show that, if the inductive energy of the loop is much smaller than the plasma frequency of the junction, the low-energy Hamiltonian of the circuit is dual to that of a topological superconducting island. These findings can inform experiments on bifluxon qubits as well as the design of novel types of protected qubits.

One-Dimensional Crystallographic Etching of Few-Layer WS$_2$. (arXiv:2310.03143v1 [])
Shisheng Li, Yung-Chang Lin, Yiling Chiew, Yunyun Dai, Zixuan Ning, Hideaki Nakajima, Hong En Lim, Jing Wu, Yasuhisa Naito, Toshiya Okazaki, Zhipei Sun, Kazu Suenaga, Yoshiki Sakuma, Kazuhito Tsukagoshi, Takaaki Taniguchi

Layer number-dependent band structures and symmetry are vital for the electrical and optical characteristics of two-dimensional (2D) transition metal dichalcogenides (TMDCs). Harvesting 2D TMDCs with tunable thickness and properties can be achieved through top-down etching and bottom-up growth strategies. In this study, we report a pioneering technique that utilizes the migration of in-situ generated Na-W-S-O droplets to etch out one-dimensional (1D) nanotrenches in few-layer WS$_2$. 1D WS$_2$ nanotrenches were successfully fabricated on the optically inert bilayer WS$_2$, showing pronounced photoluminescence and second harmonic generation signals. Additionally, we demonstrate the modulation of inkjet-printed Na$_2$WO$_4$-Na$_2$SO$_4$ particles to switch between the etching and growth modes by manipulating the sulfur supply. This versatile approach enables the creation of 1D nanochannels on 2D TMDCs. Our research presents exciting prospects for the top-down and bottom-up fabrication of 1D-2D mixed-dimensional TMDC nanostructures, expanding their use for photonic and optoelectronic applications.

Photonic molecule approach to multi-orbital topology. (arXiv:2310.03160v1 [physics.optics])
Maxim Mazanov, Diego Román-Cortés, Gabriel Cáceres-Aravena, Christofer Cid, Maxim A. Gorlach, Rodrigo A. Vicencio

The concepts of topology provide a powerful tool to tailor the propagation and localization of light. While electromagnetic waves have only two polarization states, engineered degeneracies of photonic modes provide novel opportunities resembling orbital or spin degrees of freedom in condensed matter. Here, we tailor such degeneracies for the array of femtosecond laser written waveguides in the optical range exploiting the idea of photonic molecules -- clusters of strongly coupled waveguides. In our experiments, we observe the emergence of topological modes caused by the inter-orbital coupling and track multiple topological transitions in the system with the change of the lattice spacings and excitation wavelength. This strategy opens an avenue in designing novel types of photonic topological phases and states.

Metadynamics calculations of the effect of thermal spin fluctuations on skyrmion stability. (arXiv:2310.03169v1 [cond-mat.mtrl-sci])
Ioannis Charalampidis, Joseph Barker

The stability of magnetic skyrmions has been investigated in the past, but mostly in the absence of thermal fluctuations. However, thermal spin fluctuations modify the magnetic properties (exchange stiffness, Dzyaloshinskii-Moriya interaction (DMI) and anisotropy) that define skyrmion stability. Thermal magnons also excite internal skrymion dynamics, deforming the skyrmion shape. Entropy has also been shown to modify skyrmion lifetimes in experiments, but is absent or approximated in previous studies. Here we use metadynamics to calculate the free energy surface of a magnetic thin film in terms of the topological charge and magnetization. We identify the free energy minima corresponding to different spin textures and the lowest energy paths between the ferromagnetic and single skyrmion states. We show that at low temperatures the lowest free energy barrier is a skyrmion collapse process. However, this energy barrier increases with temperature. An alternative path, where a singularity forms on the skrymion edge, has a larger free energy barrier at low temperatures but decreases with increasing temperature and eventually becomes the lowest energy barrier.

Photoconductive Effects in Single Crystals of BaZrS$_3$. (arXiv:2310.03198v1 [])
Boyang Zhao, Huandong Chen, Ragib Ahsan, Fei Hou, Eric R Hoglund, Shantanu Singh, Huan Zhao, Han Htoon, Andrey Krayev, Maruda Shanmugasundaram, Patrick E Hopkins, Jan Seidel, Rehan Kapadia, Jayakanth Ravichandran

Chalcogenide perovskites, such as BaZrS$_3$, are emerging semiconductors with potential for high photovoltaic power conversion efficiency. The role of defects in the efficiency of the generation and collection of photo-excited carriers has not been experimentally investigated extensively. We study the effect of processing-induced defects on the photoconductive properties of single crystals of BaZrS$_3$. We achieved ohmic contacts to single crystals of BaZrS$_3$ and observed positive surface photovoltage, which is typically observed in p-type semiconductors. However, mechanical polishing of BaZrS$_3$ to remove the surface oxide leads to dense deformation grain boundaries and leads to trap-dominated photoconductive response. In comparison, ohmic contacts achieved in cleaved crystals leave fewer deformation defects and greatly improve optoelectronic properties. Defect-controlled crystal growth and contact fabrication are potentially limiting factors for achieving high photon-to-excited electron conversion efficiency in BaZrS$_3$.

Efficient network exploration by means of resetting self-avoiding random walkers. (arXiv:2310.03203v1 [cond-mat.stat-mech])
Gaia Colombani, Giulia Bertagnolli, Oriol Artime

The self-avoiding random walk (SARW) is a stochastic process whose state variable avoids returning to previously visited states. This non-Markovian feature has turned SARWs a powerful tool for modelling a plethora of relevant aspects in network science, such as network navigability, robustness and resilience. We analytically characterize self-avoiding random walkers that evolve on complex networks and whose memory suffers stochastic resetting, that is, at each step, with a certain probability, they forget their previous trajectory and start free diffusion anew. Several out-of-equilibrium properties are addressed, such as the time-dependent position of the walker, the time-dependent degree distribution of the non-visited network and the first-passage time distribution, and its moments, to target nodes. We examine these metrics for different resetting parameters and network topologies, both synthetic and empirical, and find a good agreement with simulations in all cases. We also explore the role of resetting on network exploration and report a non-monotonic behavior of the cover time: frequent memory resets induce a global minimum in the cover time, significantly outperforming the well-known case of the pure random walk, while reset events that are too spaced apart become detrimental for the network discovery. Our results provide new insights into the profound interplay between topology and dynamics in complex networks, and shed light on the fundamental properties of SARWs in nontrivial environments.

Planar Hall effect in Weyl semimetals induced by pseudoelectromagnetic fields. (arXiv:2310.03209v1 [cond-mat.mes-hall])
L. Medel Onofre, A. Martín-Ruiz

The planar Hall effect (PHE), the appearance of an in-plane transverse voltage in the presence of coplanar electric and magnetic fields, has been ascribed to the chiral anomaly and Berry curvature effects in Weyl semimetals. In the presence of position- and time-dependent perturbations, such as strain, Weyl semimetals react as if they would be subjected to emergent electromagnetic fields, kwnon as pseudo-fields. In this paper we investigate the possibility of inducing nonlinear phenomena, including the PHE, in strained Weyl semimetals. Using the chiral kinetic theory in the presence of pseudo-fields, we derive general expressions for the magnetoconductivity tensor by considering the simultaneous effects of the Berry curvature and orbital magnetic moment of carriers, which are indeed of the same order of magnitude. Since pseudo-fields couple to the Weyl fermions of opposite chirality with opposite signs, we study chirality-dependent phenomena, including the longitudinal magnetoconductivity and the planar Hall effect. We discuss our results in terms of the chiral anomaly with pseudo-fields. These may open new possibilities in chiralitytronics.

Biorthogonal Majorana zero modes, extended waves in continuum of bound states and non-Hermitian Toda soliton-fermion duality. (arXiv:2310.03215v1 [hep-th])
Harold Blas

We study the non-Hermitian (NH) Toda model coupled to fermions through soliton theory techniques and the realizations of the pseudo-chiral and pseudo-Hermitian symmetries. The interplay of non-Hermiticity, integrability, nonlinearity, and topology significantly influence the formation and behavior of a continuum of bound state modes (CBM) and extended waves in the localized continuum (ELC). The non-Hermitian soliton-fermion duality, the complex scalar field topological charges and winding numbers in the spectral topology are uncovered. The Hermitian bound states/solitons lie on the unit circle $|z|=1$ defined by the uniformization parameter $z \in \IC \backslash \{0\}$ related to the complex energy eigenvalue, whereas the non-Hermitian bound states/solitons lie on the complex plane such that $|z| \neq 1$. The biorthogonal Majorana zero modes, dual to the NH Toda solitons with topological charges $\pm 1$, appear at the complex-energy point gap and are pinned at zero energy. Our findings improve the understanding of exotic quantum states, but also paves the way for future research in harnessing non-Hermitian phenomena for topological quantum computation, as well as the exploration of integrability and NH solitons in the theory of topological phases of matter.

Localization transition in non-Hermitian systems depending on reciprocity and hopping asymmetry. (arXiv:2310.03412v1 [cond-mat.dis-nn])
Daniil Kochergin, Vasilii Tiselko, Arsenii Onuchin

We investigated the single-particle Anderson localization problem for non-Hermitian systems on directed graphs. Various undirected standard random graph models were modified by controlling reciprocity and hopping asymmetry parameters. We found the emergence of left, biorthogonal and right localized states depending on both parameters and graph structure properties such as node degree $d$. For directed random graphs, the occurrence of biorthogonal localization near exceptional points is described analytically and numerically. The clustering of localized states near the center of the spectrum and the corresponding mobility edge for left and right states are shown numerically. Structural features responsible for localization, such as topologically invariant nodes or drain and sources, were also described. Considering the diagonal disorder, we observed the disappearance of localization dependence on reciprocity around $W \sim 20$ for a random regular graph $d=4$. With a small diagonal disorder, the average biorthogonal fractal dimension drastically reduces. Around $W \sim 5$ localization scars occur within the spectrum, alternating as vertical bands of clustering of left and right localized states.

Noise-Induced Phase Separation and Local Entropy Production Rate in Scalar Field Theories Driven by Persistent Noise. (arXiv:2310.03423v1 [cond-mat.stat-mech])
Matteo Paoluzzi, Demian Levis, Andrea Crisanti, Ignacio Pagonabarraga

Within the Landau-Ginzburg picture of phase transitions, scalar field theories can undergo phase separation because of a spontaneous symmetry-breaking mechanism that makes homogeneous field configurations unstable. This picture works in thermodynamics but also in the dynamics of phase separation. Here we show that scalar non-equilibrium field theories undergo phase separation just because of non-equilibrium fluctuations driven by a persistent noise. The mechanism is similar to what happens in Motility-Induced Phase Separation where persistent motion introduces an effective attractive force. In this work, we observe that Noise-Induced Phase Separation occurs in a region of the phase diagram where disordered field configurations would otherwise be stable at equilibrium. Moreover, looking at the local entropy production rate, we find that the breaking of time-reversal symmetry is concentrated on the boundary between the two phases.

Spontaneous interstitial (anti)merons in D$_{2d}$ symmetric Mn-Pt(Pd)-Sn-In system. (arXiv:2310.03427v1 [cond-mat.mtrl-sci])
Bimalesh Giri, Dola Chakrabartty, S. S. P. Parkin, Ajaya K. Nayak

Interstitial topological objects, such as skyrmions, within a natural 1-D helix are predicted to be free from ambiguous 'skyrmion Hall effect'. The helical ambience precipitate an additional potential that counteract the Magnus force arising from the gyrotropic motion of skyrmion. Here, we present the observation of $\pm$ $\frac{1}{2}$ topological charge objects (anti)merons within the 1-D helical stripes in D$_{2d}$ symmetric Mn$_{1.4}$Pt$_{0.9}$Pd$_{0.1}$Sn$_{1-x}$In$_{x}$ system. With the help of Lorentz transmission electron microscopy study we demonstrate that the pair-wise meron and antimeron chains can be spontaneously stabilized for a critical In concentration in the system. The exchange frustration induced proportionate fragmentation of the magnetic moment in the in-plane and easy-axis directions acts as a basic ingredient for the formation of (anti)merons within the helical stripe. A constrained drift motion of (anti)merons along the stripe makes this system an ideal platform for the realization of skyrmion Hall free track motion. Moreover, the observation of (anti)merons in addition to the skyrmion and antiskyrmion in D$_{2d}$ materials makes them a suitable horizon for zoo of topology.

Spin-orbit torques and spin Hall magnetoresistance generated by twin-free and amorphous Bi0.9Sb0.1 topological insulator films. (arXiv:2310.03487v1 [cond-mat.mtrl-sci])
Federico Binda, Stefano Fedel, Santos Francisco Alvarado, Paul Noël, Pietro Gambardella

Topological insulators have attracted great interest as generators of spin-orbit torques (SOTs) in spintronic devices. Bi\textsubscript{1-x}Sb\textsubscript{x} is a prominent topological insulator that has a high charge-to-spin conversion efficiency. However, the origin and magnitude of the SOTs induced by current-injection in Bi\textsubscript{1-x}Sb\textsubscript{x} remain controversial. Here we report the investigation of the SOTs and spin Hall magnetoresistance resulting from charge-to-spin conversion in twin-free epitaxial layers of Bi\textsubscript{0.9}Sb\textsubscript{0.1}(0001) coupled to FeCo, and compare it with that of amorphous Bi\textsubscript{0.9}Sb\textsubscript{0.1}. We find a large charge-to-spin conversion efficiency of 1 in the first case and less than 0.1 in the second, confirming crystalline Bi\textsubscript{0.9}Sb\textsubscript{0.1} as a strong spin injector material. The SOTs and spin Hall magnetoresistance are independent of the direction of the electric current, indicating that charge-to-spin conversion in single-crystal Bi\textsubscript{0.9}Sb\textsubscript{0.1}(0001) is isotropic despite the strong anisotropy of the topological surface states. Further, we find that the damping-like SOT has a non-monotonic temperature dependence with a minimum at 20~K. By correlating the SOT with resistivity and weak antilocalization measurements, we conclude that charge-spin conversion occurs via thermally-excited holes from the bulk states above 20~K, and conduction through the isotropic surface states with increasing spin polarization due to decreasing electron-electron scattering below 20~K.

A minimal quantum dot-based Kitaev chain with only local superconducting proximity effect. (arXiv:2310.03536v1 [cond-mat.mes-hall])
William Samuelson, Viktor Svensson, Martin Leijnse

The possibility to engineer a Kitaev chain in quantum dots coupled via superconductors has recently emerged as a promising path toward topological superconductivity and possibly nonabelian physics. Here, we show that it is possible to avoid some of the main experimental hurdles on this path by using only local proximity effect on each quantum dot in a geometry that resembles a two-dot version of the proposal in New J. Phys. 15 045020 (2013). There is no need for narrow superconducting couplers, additional Andreev bound states, or spatially varying magnetic fields; it suffices with spin-orbit interaction and a constant magnetic field, in combination with control of the superconducting phase to tune the relative strengths of elastic cotunneling and an effective crossed-Andreev-reflection-like process generated by higher-order tunneling. We use a realistic spinful, interacting model and show that high-quality Majorana bound states can be generated already in a double quantum dot.

Exotic rare earth-based materials for emerging spintronic technology. (arXiv:2310.03541v1 [cond-mat.mtrl-sci])
Sachin Gupta

The progress in materials science has always been associated with the development of functional materials systems, which enables us to design proof-of-concept devices. To advance further, theoretical predictions of new novel materials and their experimental realization is very important. This chapter reviews the intriguing properties of rare earth-based materials and their applications in spintronics. Spintronics is an emerging technology, which exploits spin degree of freedom of an electron along with its charge property. Discovery of various physical phenomena and their industrial applications in the field of magnetic sensors, magnetic recording and non-volatile memories such as magnetic random access memory (MRAM) and spin-transfer torque (STT) MRAM opens several new directions in this field. Materials with large spin polarization, strong spin-orbit coupling, and tunable electronic and magnetic properties offer an excellent platform for the spintronics technology. Combination of rare earths with other elements such as transition metals show broad range of structural, electronic, and magnetic properties which make them excellent candidates for various spintronic applications. This chapter discusses many such materials ranging from Heusler alloys, topological insulators to two-dimensional ferromagnets and their potential applications. The review gives an insight of how rare-earth materials can play a key role in emerging future technology and have great potential in many new spintronic related applications.

Localization of Dirac modes in the $\mathrm{SU}(2)$-Higgs model at finite temperature. (arXiv:2310.03542v1 [hep-lat])
György Baranka, Matteo Giordano

We investigate the connection between localization of low-lying Dirac modes and Polyakov-loop ordering in the lattice $\mathrm{SU}(2)$-Higgs model at finite temperature, probed with static external staggered fermions. After mapping out the phase diagram of the model at a fixed temporal extension in lattice units, we study the localization properties of the low-lying modes of the staggered Dirac operator, how these properties change across the various transitions, and how these modes correlate with the gauge and Higgs fields. We find localized low modes in the deconfined and in the Higgs phase, where the Polyakov loop is strongly ordered, but in both cases they disappear as one crosses over to the confined phase. Our findings confirm the general expectations of the "sea/islands" picture, and the more detailed expectations of its refined version concerning the favorable locations of localized modes, also in the presence of dynamical scalar matter.

Observation of topologically distinct corner states in "bearded" photonic Kagome lattices. (arXiv:2310.03558v1 [physics.optics])
Limin Song, Domenico Bongiovanni, Zhichan Hu, Ziteng Wang, Shiqi Xia, Liqin Tang, Daohong Song, Roberto Morandotti, Zhigang Chen

Kagome lattices represent an archetype of intriguing physics, attracting a great deal of interest in different branches of natural sciences, recently in the context of topological crystalline insulators. Here, we demonstrate two distinct classes of corner states in breathing Kagome lattices (BKLs) with "bearded" edge truncation, unveiling their topological origin. The in-phase corner states are found to exist only in the topologically nontrivial regime, characterized by a nonzero bulk polarization. In contrast, the out-of-phase corner states appear in both topologically trivial and nontrivial regimes, either as bound states in the continuum or as in-gap states depending on the lattice dimerization conditions. Furthermore, the out-of-phase corner states are highly localized, akin to flat-band compact localized states, and they manifest both real- and momentum-space topology. Experimentally, we observe both types of corner states in laser-written photonic bearded-edge BKLs, corroborated by numerical simulations. Our results not only deepen the current understanding of topological corner modes in BKLs, but also provide new insight into their physical origins, which may be applied to other topological BKL platforms beyond optics.

Anomalous Hall effect by chiral spin textures in two-dimensional Luttinger model. (arXiv:2310.03576v1 [cond-mat.mes-hall])
Ryunosuke Terasawa, Hiroaki Ishizuka

Long-range magnetic textures, such as magnetic skyrmion, give rise to rich transport properties in magnetic metals, such as the anomalous Hall effect related to spin chirality, a.k.a. topological Hall effect. In addition to the topological Hall effect, recent studies on non-centrosymmetric magnets find that the spin-orbit interaction of itinerant electrons gives rise to novel contributions related to spin chirality, i.e., the chiral Hall effect. In this work, we discuss that the spin-orbit interaction has a distinct, yet significant, effect on the anomalous Hall effect related to spin chirality in centrosymmetric magnets. Using a scattering theory method, we find that the anomalous Hall effect related to scalar spin chirality in a two-dimensional Luttinger model is suppressed by more than one order of magnitude compared to the quadratic dispersion, and the contributions similar to the chiral Hall effect in Rashba model vanishes. At the same time, a novel term that gives different Hall conductivity for the Bloch and Neel skyrmions occurs, thereby enabling the detection of the skyrmion helicity. The striking differences demonstrate the rich effect of crystal symmetry on the chirality-related anomalous Hall effect in materials with strong spin-orbit interaction.

Unconventional superconductivity in Sc$_2$Ir$_{4-x}$Si$_x$ by spin-orbit coupling driven flat band. (arXiv:2310.03609v1 [cond-mat.supr-con])
Zhengyan Zhu, Yuxiang Wu, Shengtai Fan, Yiliang Fan, Yiwen Li, Yongze Ye, Xiyu Zhu, Haijun Zhang, Hai-Hu Wen

The kagome lattice is very attractive as it can host many novel quantum states, such as the charge density wave, superconductivity, quantum spin liquid, etc. Meanwhile, iridates often exhibit a strong spin-orbit coupling (SOC) effect due to the large atomic mass of 5$d$ elements, which has important implications for both the energy bands and the pairing symmetry of superconductors. For the Laves phase superconductor Sc$_2$Ir$_4$ with a kagome lattice, by doping Si to the Ir sites, we observed a nonmonotonic and two-dome like doping dependence of the superconducting transition temperature $T_{\rm c}$, which is typically found in many unconventional superconducting systems. Interestingly, for some samples, especially Sc$_2$Ir$_{3.5}$Si$_{0.5}$ with the optimal $T_{\rm c}$, after the suppression of superconductivity, the normal-state resistivity exhibits a semiconducting behavior; meanwhile, the specific heat coefficient shows an upturn which follows the relation $C/T\propto{\rm ln}(T_0/T)$ at low temperatures. Around the optimal doping, the resistance measurements exhibit strong superconducting fluctuations. And the superconductivity related specific heat can be fitted by the model of a $d$-wave gap after subtracting the normal-state background. These strongly suggest unconventional superconductivity and correlation effect in the samples, which is mainly induced by a flat band near the Fermi level when considering the SOC, as supported by the first-principles calculations. Our results reveal a new unconventional superconducting system Sc$_2$Ir$_{4-x}$Si$_x$ with strong correlation effects induced by the flat band in the kagome system with strong SOC.

The exact evaluation of hexagonal spin-networks and topological quantum neural networks. (arXiv:2310.03632v1 [quant-ph])
Matteo Lulli, Antonino Marciano, Emanuele Zappala

The physical scalar product between spin-networks has been shown to be a fundamental tool in the theory of topological quantum neural networks (TQNN), which are quantum neural networks previously introduced by the authors in the context of quantum machine learning. However, the effective evaluation of the scalar product remains a bottleneck for the applicability of the theory. We introduce an algorithm for the evaluation of the physical scalar product defined by Noui and Perez between spin-network with hexagonal shape. By means of recoupling theory and the properties of the Haar integration we obtain an efficient algorithm, and provide several proofs regarding the main steps. We investigate the behavior of the TQNN evaluations on certain classes of spin-networks with the classical and quantum recoupling. All results can be independently reproduced through the ``idea.deploy" framework~\href{}{\nolinkurl{}}

Interacting nodal semimetals with non-linear bands. (arXiv:2310.03653v1 [cond-mat.str-el])
Arianna Poli, Niklas Wagner, Max Fischer, Alessandro Toschi, Giorgio Sangiovanni, Sergio Ciuchi

We investigate the quasi-particle and transport properties of a model describing interacting Dirac and Weyl semimetals in the presence of local Hubbard repulsion $U$, where we explicitly include a deviation from the linearity of the energy-momentum dispersion through an intermediate-energy scale $\Lambda$. Our focus lies on the correlated phase of the semimetal. At the nodal point, the renormalization of spectral weight at a fixed temperature $T$ exhibits a weak dependence on $\Lambda$ but is sensitive to the proximity to the Mott transition. Conversely, the scattering rate of quasi-particles and the resistivity display high-temperature exponents that crucially rely on $\Lambda$, leading to a crossover towards a conventional Fermi-liquid behaviour at finite T. Finally, by employing the Nernst-Einstein relation for conductivity, we identify a corresponding density crossover as a function of the chemical potential.

Topological Density Correlations in a Fermi Gas. (arXiv:2310.03737v1 [cond-mat.quant-gas])
Pok Man Tam, Charles L. Kane

A Fermi gas of non-interacting electrons, or ultra-cold fermionic atoms, has a quantum ground state defined by a region of occupancy in momentum space known as the Fermi sea. The Euler characteristic $\chi_F$ of the Fermi sea serves to topologically classify these gapless fermionic states. The topology of a $D$ dimensional Fermi sea is physically encoded in the $D+1$ point equal time density correlation function. In this work, we first present a simple proof of this fact by showing that the evaluation of the correlation function can be formulated in terms of a triangulation of the Fermi sea with a collection of points, links and triangles and their higher dimensional analogs. We then make use of the topological $D+1$ point density correlation to reveal universal structures of the more general $M$ point density correlation functions in a $D$ dimensional Fermi gas. Two experimental methods are proposed for observing these correlations in $D=2$. In cold atomic gases imaged by quantum gas microscopy, our analysis supports the feasibility of measuring the third order density correlation, from which $\chi_F$ can be reliably extracted in systems with as few as around 100 atoms. For solid-state electron gases, we propose measuring correlations in the speckle pattern of intensity fluctuations in nonlinear X-ray scattering experiments.

Hunting for quantum-classical crossover in condensed matter problems. (arXiv:2210.14109v2 [quant-ph] UPDATED)
Nobuyuki Yoshioka, Tsuyoshi Okubo, Yasunari Suzuki, Yuki Koizumi, Wataru Mizukami

The intensive pursuit for quantum advantage in terms of computational complexity has further led to a modernized crucial question: {\it When and how will quantum computers outperform classical computers?} The next milestone is undoubtedly the realization of quantum acceleration in practical problems. Here we provide a clear evidence and arguments that the primary target is likely to be condensed matter physics. Our primary contributions are summarized as follows: 1) Proposal of systematic error/runtime analysis on state-of-the-art classical algorithm based on tensor networks; 2) Dedicated and high-resolution analysis on quantum resource performed at the level of executable logical instructions; 3) Clarification of quantum-classical crosspoint for ground-state simulation to be within runtime of hours using only a few hundreds of thousand physical qubits for 2d Heisenberg and 2d Fermi-Hubbard models, assuming that logical qubits are encoded via the surface code with the physical error rate of $p=10^{-3}$. To our knowledge, we argue that condensed matter problems offer the earliest platform for demonstration of practical quantum advantage that is order-of-magnitude more feasible than ever known candidates, in terms of both qubit counts and total runtime.

Homotopy Classification of loops of Clifford unitaries. (arXiv:2306.09903v2 [math-ph] UPDATED)
Roman Geiko, Yichen Hu

Clifford quantum circuits are elementary invertible transformations of quantum systems that map Pauli operators to Pauli operators. We study periodic one-parameter families of Clifford circuits, called loops of Clifford circuits, acting on $\mathsf{d}$-dimensional lattices of prime $p$-dimensional qudits. We propose to use the notion of algebraic homotopy to identify topologically equivalent loops. We calculate homotopy classes of such loops for any odd $p$ and $\mathsf{d}=0,1,2,3$, and $4$. Our main tool is the Hermitian K-theory, particularly a generalization of the Maslov index from symplectic geometry. We observe that the homotopy classes of loops of Clifford circuits in $(\mathsf{d}+1)$-dimensions coincide with the quotient of the group of Clifford Quantum Cellular Automata modulo shallow circuits and lattice translations in $\mathsf{d}$-dimensions.

Weak first-order phase transitions in the frustrated square lattice J1-J2 classical Ising model. (arXiv:2306.12021v3 [cond-mat.stat-mech] UPDATED)
Adil A. Gangat

The classical $J_1$-$J_2$ Ising model on the square lattice is a minimal model of frustrated magnetism whose phase boundary is not yet completely understood. The current consensus is that the phase transitions are continuous when $J_2/|J_1|\gtrsim0.67$, while strong evidence is lacking for the order of the transitions at $0<J_2/|J_1|\lesssim0.67$. We point out a loop hole in the argument for the current consensus, and we find strong evidence that the phase boundary is (mostly weak) first-order at $0.5<J_2/|J_1|<\infty$ such that it asymptotically becomes second-order when $J_2/|J_1|\rightarrow\infty$. We also find suggestive evidence that when $J_2/|J_1|\rightarrow0.5^+$, the phase boundary becomes of a novel first-order type that is neither strong nor weak. We establish these results by combining adiabatic evolution of tensor networks directly in the thermodynamic limit with the theory of finite entanglement scaling.

Reversal of the skyrmion topological deflection across ferrimagnetic angular momentum compensation. (arXiv:2307.04669v2 [cond-mat.mtrl-sci] UPDATED)
L. Berges, R. Weil, A. Mougin, J. Sampaio

Due to their non-trivial topology, skyrmions describe deflected trajectories, which hinders their straight propagation in nanotracks and can lead to their annihilation at the track edges. This deflection is caused by a gyrotropic force proportional to the topological charge and the angular momentum density of the host film. In this article we present clear evidence of the reversal of the topological deflection angle of skyrmions with the sign of angular momentum density. We measured the skyrmion trajectories across the angular momentum compensation temperature (TAC) in GdCo thin films, a rare earth/transition metal ferrimagnetic alloy. The sample composition was used to engineer the skyrmion stability below and above the TAC. A refined comparison of their dynamical properties evidenced a reversal of the skyrmions deflection angle with the total angular momentum density. This reversal is a clear demonstration of the possibility of tuning the skyrmion deflection angle in ferrimagnetic materials and paves the way for deflection-free skyrmion devices.

Minimal alternating current injection into carbon nanotubes. (arXiv:2307.11943v3 [cond-mat.mes-hall] UPDATED)
Kota Fukuzawa, Takeo Kato, Thibaut Jonckheere, Jérôme Rech, Thierry Martin

We study theoretically the effect of electronic interactions in 1d systems on electron injection using periodic Lorentzian pulses, known as Levitons. We consider specifically a system composed of a metallic single-wall carbon nanotube, described with the Luttinger liquid formalism, a scanning tunneling microscope (STM) tip, and metallic leads. Using the out-of-equilibrium Keldysh Green function formalism, we compute the current and current noise in the system. We prove that the excess noise vanishes when each Leviton injects an integer number of electrons from the STM tip into the nanotube. This extends the concept of minimal injection with Levitons to strongly correlated, uni-dimensional non-chiral systems. We also study the time-dependent current profile, and show how it is the result of interferences between pulses non-trivially reflected at the nanotube-lead interface.

Found 6 papers in prb
Date of feed: Fri, 06 Oct 2023 03:17:05 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]+)|(flatband)|(flat.{1}band)|(LK.{1}99)

Strong Dzyaloshinskii-Moriya interaction in two-dimensional magnets via lithium absorption
Cheng Ma, Kuijuan Jin, Chen Ge, Er-Jia Guo, Can Wang, and Xiulai Xu
Author(s): Cheng Ma, Kuijuan Jin, Chen Ge, Er-Jia Guo, Can Wang, and Xiulai Xu

Dzyaloshinskii-Moriya interaction (DMI) is of particular interest as it plays a primary role in stabilizing topological chiral magnetism such as skyrmions and has been intensively studied due to its potential applications for next-generation information storage technologies. For two-dimensional (2D)…

[Phys. Rev. B 108, 134405] Published Thu Oct 05, 2023

Effect of random antiferromagnetic exchange on the spin waves in a three-dimensional Heisenberg ferromagnet
S. Hameed, Z. Wang, D. M. Gautreau, J. Joe, K. P. Olson, S. Chi, P. M. Gehring, T. Hong, D. M. Pajerowski, T. J. Williams, Z. Xu, M. Matsuda, T. Birol, R. M. Fernandes, and M. Greven
Author(s): S. Hameed, Z. Wang, D. M. Gautreau, J. Joe, K. P. Olson, S. Chi, P. M. Gehring, T. Hong, D. M. Pajerowski, T. J. Williams, Z. Xu, M. Matsuda, T. Birol, R. M. Fernandes, and M. Greven

Neutron scattering is used to study spin waves in the three-dimensional Heisenberg ferromagnet ${\mathrm{YTiO}}_{3}$, with spin-spin exchange disorder introduced via La substitution at the Y site. No significant changes are observed in the spin-wave dispersion up to a La concentration of 20%. Howeve…

[Phys. Rev. B 108, 134406] Published Thu Oct 05, 2023

Conductivity in flat bands from the Kubo-Greenwood formula
Kukka-Emilia Huhtinen and Päivi Törmä
Author(s): Kukka-Emilia Huhtinen and Päivi Törmä

Conductivity in a multiband system can be divided into intra- and interband contributions, and the latter further into symmetric and antisymmetric parts. In a flat band, intraband conductivity vanishes and the antisymmetric interband contribution, proportional to the Berry curvature, corresponds to …

[Phys. Rev. B 108, 155108] Published Thu Oct 05, 2023

Spatially dispersive helicity-dependent photocurrent in Dirac semimetal ${\mathrm{Cd}}_{3}{\mathrm{As}}_{2}$ nanobelts
Bob Minyu Wang, Yuqing Zhu, Henry Clark Travaglini, Renzhi Sun, Sergey Y. Savrasov, William Hahn, Klaus van Benthem, and Dong Yu
Author(s): Bob Minyu Wang, Yuqing Zhu, Henry Clark Travaglini, Renzhi Sun, Sergey Y. Savrasov, William Hahn, Klaus van Benthem, and Dong Yu

Dirac semimetals (DSMs) have demonstrated many exotic properties, such as high carrier mobility, 3D quantum spin Hall effect, and topologically protected spin transport. However, their spin degeneracy has inhibited widespread applications in spintronics and quantum devices. Using a helicity-dependent photocurrent (HDPC), the authors demonstrate here spin generation in strain-free DSM Cd3As2 nanobelt field effect transistors at room temperature. The observed HDPC is attributed to spin-polarized Fermi arcs at the surface. This work provides key insights on light-controlled spin manipulation in Dirac materials.

[Phys. Rev. B 108, 165405] Published Thu Oct 05, 2023

Charge-resolved entanglement in the presence of topological defects
Dávid X. Horváth, Shachar Fraenkel, Stefano Scopa, and Colin Rylands
Author(s): Dávid X. Horváth, Shachar Fraenkel, Stefano Scopa, and Colin Rylands

Topological excitations or defects such as solitons are ubiquitous throughout physics, supporting numerous interesting phenomena like zero-energy modes with exotic statistics and fractionalized charges. In this paper, we study such objects through the lens of symmetry-resolved entanglement entropy. …

[Phys. Rev. B 108, 165406] Published Thu Oct 05, 2023

Thermal difference reflectivity of tilted two-dimensional Dirac materials
M. A. Mojarro, R. Carrillo-Bastos, and Jesús A. Maytorena
Author(s): M. A. Mojarro, R. Carrillo-Bastos, and Jesús A. Maytorena

Deviation from perfect conical dispersion in Dirac materials, such as the presence of mass or tilting, enhances the control and directionality of electronic transport. To identify these signatures, we analyze the thermal derivative spectra of optical reflectivity in doped massive tilted Dirac system…

[Phys. Rev. B 108, L161401] Published Thu Oct 05, 2023

Found 1 papers in prl
Date of feed: Fri, 06 Oct 2023 03:17:06 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]+)|(flatband)|(flat.{1}band)|(LK.{1}99)

Gate-Defined Topological Josephson Junctions in Bernal Bilayer Graphene
Ying-Ming Xie, Étienne Lantagne-Hurtubise, Andrea F. Young, Stevan Nadj-Perge, and Jason Alicea
Author(s): Ying-Ming Xie, Étienne Lantagne-Hurtubise, Andrea F. Young, Stevan Nadj-Perge, and Jason Alicea

Gapped superconductivity emerging via intervalley coherence in bilayer graphene or monolayer WSe2 can lead to formation of Majorana zero modes.

[Phys. Rev. Lett. 131, 146601] Published Thu Oct 05, 2023

Found 1 papers in acs-nano
Date of feed: Thu, 05 Oct 2023 13:07:20 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]+)|(flatband)|(flat.{1}band)|(LK.{1}99)

[ASAP] Laser-Induced MXene-Functionalized Graphene Nanoarchitectonics-Based Microsupercapacitor for Health Monitoring Application
Sujit Deshmukh, Kalyan Ghosh, Martin Pykal, Michal Otyepka, and Martin Pumera

TOC Graphic

ACS Nano
DOI: 10.1021/acsnano.3c07319

Found 1 papers in sci-rep

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]+)|(flatband)|(flat.{1}band)|(LK.{1}99)

Efficient oxidation of sulfides to sulfoxides catalyzed by heterogeneous Zr-containing polyoxometalate grafted on graphene oxide
Masoud Mirzaei

Scientific Reports, Published online: 05 October 2023; doi:10.1038/s41598-023-43985-z

Efficient oxidation of sulfides to sulfoxides catalyzed by heterogeneous Zr-containing polyoxometalate grafted on graphene oxide

Found 1 papers in comm-phys

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]+)|(flatband)|(flat.{1}band)|(LK.{1}99)

Dynamical and topological properties of the spin angular momenta in general electromagnetic fields
Xiaocong Yuan

Communications Physics, Published online: 05 October 2023; doi:10.1038/s42005-023-01374-y

The task of mapping solid-state spin-orbit coupling (SOC) into photonic systems has sparked intense research efforts. The authors propose a unified theory to study SOC in photonic and classical wave systems, that is validated numerically and through ad hoc experiments with Bloch-type photonic skyrmions, showing excellent agreement between the two.