Found 29 papers in cond-mat
Date of feed: Fri, 22 Sep 2023 00:30:00 GMT

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On the dynamical stability of copper-doped lead apatite. (arXiv:2309.11541v1 [cond-mat.supr-con])
Sun-Woo Kim, Kang Wang, Siyu Chen, Lewis J. Conway, G. Lucian Pascut, Ion Errea, Chris J. Pickard, Bartomeu Monserrat

The recent claim of room temperature superconductivity in a copper-doped lead apatite compound, called LK-99, has sparked remarkable interest and controversy. Subsequent experiments have largely failed to reproduce the claimed superconductivity, while theoretical works have identified multiple key features including strong electronic correlation, structural instabilities, and dopability constraints. A puzzling claim of several recent theoretical studies is that both parent and copper-doped lead apatite structures are dynamically unstable at the harmonic level, questioning decades of experimental reports of the parent compound structures and the recently proposed copper-doped structures. In this work, we demonstrate that both parent and copper-doped lead apatite structures are dynamically stable at room temperature. Anharmonic phonon-phonon interactions play a key role in stabilizing some copper-doped phases, while most phases are largely stable even at the harmonic level. We also show that dynamical stability depends on both volume and correlation strength, suggesting controllable ways of exploring the copper-doped lead apatite structural phase diagram. Our results fully reconcile the theoretical description of the structures of both parent and copper-doped lead apatite with experiment.


Distinct quasiparticle excitations in single-particle spectral function. (arXiv:2309.11556v1 [cond-mat.str-el])
Jing-Yu Zhao, Zheng-Yu Weng

Recent scanning tunneling microscopy (STM) measurements have observed a multi-peak energy structure on the positive bias side in dilute-hole-doped cuprates, where tightly-bound hole pairs are identified as the building blocks that can continuously persist into the superconducting regime. In this work, we study the single-particle spectral function based on a two-hole ground state wavefunction [Phys. Rev. X 12, 011062 (2022)], which can provide a consistent understanding of the experimental results. Here the wavefunction structure with a dichotomy of $d$-wave Cooper pairing and $s$-wave ``twisted hole'' pairing will lead to two branches in the local spectral function where the low-lying one corresponds to a conventional nodal quasiparticle, and a higher energy branch is associated with a ``twisted'' quasiparticle above the pair breaking or ``pseudogap'' energy. These energies can be further extended into energy spectra in the momentum space, in which the low-energy dispersion agrees excellently with the Quantum Monte Carlo numerical result. The implications for the STM spectra in the superconducting state will also be discussed.


Superconducting triangular islands as a platform for manipulating Majorana zero modes. (arXiv:2309.11607v1 [cond-mat.mes-hall])
Aidan Winblad, Hua Chen

Current proposals for topological quantum computation (TQC) based on Majorana zero modes (MZM) have mostly been focused on coupled-wire architecture which can be challenging to implement experimentally. To explore alternative building blocks of TQC, in this work we study the possibility of obtaining robust MZM at the corners of triangular superconducting islands, which often appear spontaneously in epitaxial growth. We first show that a minimal three-site triangle model of spinless $p$-wave superconductor allows MZM to appear at different pairs of vertices controlled by a staggered vector potential, which may be realized using coupled quantum dots and can already demonstrate braiding. For systems with less fine-tuned parameters, we suggest an alternative structure of a "hollow" triangle subject to uniform supercurrents or vector potentials, in which MZM generally appear when two of the edges are in a different topological phase from the third. We also discuss the feasibility of constructing the triangles using existing candidate MZM systems and of braiding more MZM in networks of such triangles.


Topological Floquet Flat Bands in Irradiated Alternating Twist Multilayer Graphene. (arXiv:2309.11685v1 [cond-mat.mes-hall])
Yingyi Huang

We study the appearance of topological Floquet flat bands in alternating-twist multilayer graphene (ATMG) which has an alternating relative twist angle $\pm\theta$ near the first magic angle. While the system hosts both flat bands and a steep Dirac cone in the static case, the circularly polarized laser beam can open a gap at the Moir\'{e} $K$ point and create Floquet flat bands carrying non-zero Chern numbers. Considering the recent lattice-relaxation results, we find that the topological flat band is well-isolated for the effective interlayer tunneling in $n=3, 4, 5$ layer. Such dynamically produced topological flat bands are potentially observed in the experiment and thus provide a feasible way to realize the fractional Chern insulator.


A local criterion of topological phase transitions. (arXiv:2309.11738v1 [cond-mat.stat-mech])
Yangfan Hu

A local criterion of topological phase transitions is established based on the Morse theory: a topological phase transition occurs when the count of Morse critical points of the order function changes. The locations in space where this change occurs are referred to as spatial critical points of the topological phase transition. In cases of continuous topological phase transitions, these spatial critical points are identified through the emergence of degenerate Morse critical points, where local maxima and minima of the order function split or merge. This resembles the formation and annihilation of a particle-antiparticle pair. The wide-ranging applicability of this criterion is demonstrated through three case studies that explore topological phase transitions in both configuration space and reciprocal space. Every topological phase transition is linked to a localized physical process that cannot be comprehended solely by studying changes in a global quantity, such as a topological invariant.


Separability transitions in topological states induced by local decoherence. (arXiv:2309.11879v1 [quant-ph])
Yu-Hsueh Chen, Tarun Grover

We study states with intrinsic topological order subjected to local decoherence from the perspective of separability, i.e., whether a decohered mixed state can be expressed as an ensemble of short-range entangled pure states. We focus on toric codes and the X-cube fracton state and provide evidence for the existence of decoherence-induced separability transitions that precisely coincide with the error-recovery transitions. A key insight is that local decoherence acting on the 'parent' cluster states of these models results in a Gibbs state.


Entanglement R\'enyi entropy and boson-fermion duality in massless Thirring model. (arXiv:2309.11889v1 [hep-th])
Harunobu Fujimura, Tatsuma Nishioka, Soichiro Shimamori

We investigate the second R\'enyi entropy of two intervals in the massless Thirring model describing a self-interacting Dirac fermion in two dimensions. Boson-fermion duality relating this model to a free compact boson theory enables us to simplify the calculation of the second R\'enyi entropy, reducing it to the evaluation of the partition functions of the bosonic theory on a torus. We derive exact results on the second R\'enyi entropy, and examine the dependence on the sizes of the intervals and the coupling constant of the model both analytically and numerically. We also explore the mutual R\'enyi information, a measure quantifying the correlation between the two intervals, and find that it generally increases as the coupling constant of the Thirring model becomes larger.


Conformal field theory approach to parton fractional quantum Hall trial wave functions. (arXiv:2309.11910v1 [cond-mat.str-el])
Greg J. Henderson, G. J. Sreejith, Steven H. Simon

We show that all lowest Landau level projected and unprojected chiral parton type fractional quantum Hall ground and edge state trial wave functions, which take the form of products of integer quantum Hall wave functions, can be expressed as conformal field theory (CFT) correlation functions, where we can associate a chiral algebra to each state which defines a CFT that is the ``smallest'' such CFT that can generate the corresponding ground and edge state trial wave functions. A field-theoretic generalisation of Laughlin's plasma analogy, known as generalised screening, is formulated for these states. If this holds, along with an additional assumption, we argue that the inner products of edge state trial wave functions, for parton states with a unique densest wave function, can be expressed as matrix elements of an exponentiated local action operator of the CFT, generalising the result of Dubail et al. [PRB 85, 11531 (2012)], which implies the equality between edge state and entanglement level counting to state counting in the CFT. We numerically test this result in the case of the unprojected $\nu = 2/5$ composite fermion state and the bosonic $\nu = 1$ $\phi_2^2$ parton state. We discuss how Read's arguments [PRB 79, 045308 (2009)] still apply, implying that conformal blocks of the CFT defined by the given chiral algebra are valid quasi-hole trial wave functions, with the adiabatic braiding statistics given by the monodromy of these functions. It is shown that all chiral composite fermion wave functions can be expressed as CFT correlation functions without explicit symmetrisation and that the ground, edge, and quasi-hole trial wave functions of the $\phi_n^m$ parton states can be expressed as the conformal blocks of the $U(1) \otimes SU(n)_m$ WZW models. We discuss the $\phi_2^k$ series in detail, where several examples of quasi-hole braiding statistics calculations are given.


Origin of electrical noise near charge neutrality in dual gated graphene device. (arXiv:2309.12011v1 [cond-mat.mes-hall])
Aaryan Mehra, Roshan Jesus Mathew, Chandan Kumar

This letter investigates low frequency 1/ f noise in hBN encapsulated graphene device in a dual gated geometry. The noise study is performed as a function of top gate carrier density (nT G) at different back gate densities (nBG). The noise at low nBG is found to be independent of top gate carrier density. With increasing nBG, noise value increases and a noise peak is observed near charge inhomogeneity of the device. Further increase in nBG leads to decrease in noise magnitude. The shape of the noise is found to be closely related to charge inhomogeneity region of the device. Moreover, the noise and conductivity data near charge neutrality shows clear evidence of noise emanating from combination of charge number and mobility fluctuation


Electrostatic tuning of bilayer graphene edge modes. (arXiv:2309.12013v1 [cond-mat.mes-hall])
Hira Ali, Llorenç Serra

We study the effect of a local potential shift induced by a side electrode on the edge modes at the boundary between gapped and ungapped bilayer graphene. A potential shift close to the gapped-ungapped boundary causes the emergence of unprotected edge modes, propagating in both directions along the boundary. These counterpropagating edge modes allow edge backscattering, as opposed to the case of valley-momentum-locked edge modes. We then calculate the conductance of a bilayer graphene wire in presence of finger-gate electrodes, finding strong asymmetries with energy inversion and deviations from conductance quantization that can be understood with the gate-induced unprotected edge modes.


VO$_2$ under hydrostatic pressure: Isostructural phase transition close to a critical end-point. (arXiv:2309.12020v1 [cond-mat.str-el])
P. Bouvier, L. Bussmann, D. Machon, I. Breslavetz, G. Garbarino, P. Strobel, V. Dmitriev

The high-pressure behavior of monoclinic VO$_2$ is revisited by a combination of Raman spectroscopy and X-ray diffraction on a single crystal under hydrostatic conditions at room temperature. A soft mode is observed up to P$_c$ = 13.9(1) GPa. At this pressure, an isostructural phase transition between two monoclinic phases M$_1$ and M$_1$' hinders this instability. The features of this transformation (no apparent volume jump) indicate that the compression at ambient temperature passes close to a critical point. An analysis based on the Landau theory of phase transitions gives a complete description of the P-T phase diagram. The M1' is characterized by spontaneous displacements of the oxygen sub-lattice without any strong modification of the VV dimers distances nor the twist angle of vanadium chains. The spontaneous displacements of oxygen and the spontaneous deformations of the ($b_{M1}$, $c_{M1}$) plane follow the same quadratic dependence with pressure and scales with spontaneous shifts of the Raman phonons located at 225, 260 and 310 cm$^{-1}$. Pressure-induced shifts of the Raman peaks allows for new assignment of several Raman modes. In particular, the A$_g$(1)+B$_g$(1) modes at 145 cm$^{-1}$ are identified as the vanadium displacive phonons. A second transformation in the metallic phase X, which is found triclinic (P$\bar1$) is observed starting at 32 GPa, with a wide coexistence region (up to 42 GPa). Upon decompression, phase X transforms, between 20 GPa and 3 GPa, to another phase that is neither the M$_1$' nor M$_1$ phase. The structural transitions identified under pressure match with all the previously reported electronic modifications confirming that lattice and electronic degrees of freedom are closely coupled in this correlated material.


Pair Production in time-dependent Electric field at Finite times. (arXiv:2309.12079v1 [hep-ph])
Deepak, Manoranjan P. Singh

We investigate the finite-time behavior of pair production from the vacuum by a time-dependent Sauter pulsed electric field using the spinor quantum electrodynamics (QED). In the adiabatic basis, the one-particle distribution function in momentum space is determined by utilizing the exact analytical solution of the Dirac equation. By examining the temporal behavior of the one-particle distribution function and the momentum spectrum of created pairs in the sub-critical field limit $(E_0 = 0.2E_c)$, we observe oscillatory patterns in the longitudinal momentum spectrum(LMS) of particles at finite times. These oscillations arise due to quantum interference effects resulting from the dynamical tunneling. Furthermore, we derive an approximate and simplified analytical expression for the distribution function at finite times, which allows us to explain the origin and behavior of these oscillations. Additionally, we discuss the role of the vacuum polarization function and its counter term to the oscillations in LMS vacuum excitation. We also analyse the transverse momentum spectrum (TMS).


Persistent current-carrying state of charge quasuparticles in $np$-ribbon featuring single Dirac cone. (arXiv:2309.12084v1 [cond-mat.mes-hall])
Anatoly M. Kadigrobov, Ilya M. Eremin

The formation of persistent charge currents in mesoscopic systems remains an interesting and actual topic of condensed matter research. Here, we analyze the formation of spontaneous arising persistent currents of charged fermions in 2-dimensional electron-hole ribbons on the top and bottom of a 3-dimensional topological insulator. In such a device the two-dimensional Dirac fermions with opposite chiralities are spatially separated that allows these currents to flow in the opposite directions without compensating each other. The nature of this phenomenon is based on the interference of the quasiparticle quantum waves which are scattered with asymmetric scattering phases at the lateral n-p chiral junction and then reflected back by the external boundaries of the ribbon. As a result quasiparticles in the ribbon are shown to be in unified electron-hole quantum states carrying the persistent current.


Individually tunable tunnelling coefficients in optical lattices using local periodic driving. (arXiv:2309.12124v1 [cond-mat.quant-gas])
Georgia M. Nixon, F. Nur Unal, Ulrich Schneider

Ultracold atoms in optical lattices have emerged as powerful quantum simulators of translationally invariant systems with many applications in e.g. strongly-correlated and topological systems. However, the ability to locally tune all Hamiltonian parameters remains an outstanding goal that would enable the simulation of a wider range of quantum phenomena. Motivated by recent advances in quantum gas microscopes and optical tweezers, we here show theoretically how local control over individual tunnelling links in an optical lattice can be achieved by incorporating local time-periodic potentials. We propose to periodically modulate the on-site energy of individual lattice sites and employ Floquet theory to demonstrate how this can result in full individual control over the tunnelling amplitudes in one dimension. We provide various example configurations realising interesting topological models such as extended Su-Schrieffer-Heeger models that would be challenging to realize by other means. Extending to two dimensions, we present that local periodic driving in a three-site plaquette allows for full simultaneous control over the relative tunnelling amplitudes and the gauge-invariant flux piercing the plaquette, providing a clear stepping stone in building a fully programmable 2D tight-binding model. This local modulation scheme is applicable to many different lattice geometries.


Intertype superconductivity evoked by the interplay of disorder and multiple bands. (arXiv:2309.12133v1 [cond-mat.supr-con])
P. M. Marychev, A. A. Shanenko, A. Vagov

Nonmagnetic impurity scattering is known to shift up the Ginzburg-Landau parameter $\kappa$ of a superconductor. In this case, when the system is initially in type I, it can change its magnetic response, crossing the intertype domain with $\kappa \sim 1$ between the two standard superconductivity types and arriving at type II. In the present work we demonstrate that the impact of disorder can be much more profound in the presence of the multiband structure of the charge carrier states. In particular, when the band diffusivities differ from each other, the intertype domain tends to expand significantly, including points with $\kappa \gg 1$ that belong to deep type-II in conventional single-band superconductors. Our finding sheds light on the nontrivial disorder effect and significantly complements earlier results on the enlargement of the intertype domain in clean multiband superconductors.


Band Flattening and Overlap Fermion. (arXiv:2309.12174v1 [hep-th])
Taro Kimura, Masataka Watanabe

We show that, for each symmetry class based on the tenfold way classification, the effective Dirac operator obtained by integrating out the additional bulk direction takes a value in the corresponding classifying space, from which we obtain the flat band Hamiltonian. We then obtain the overlap Dirac operator for each symmetry class and establish the Ginsparg--Wilson relation associated with $\mathcal{C}$ and $\mathcal{T}$ symmetries, and also the mod-two index theorem.


Electrical operation of hole spin qubits in planar MOS silicon quantum dots. (arXiv:2309.12243v1 [cond-mat.mes-hall])
Zhanning Wang, Abhikbrata Sarkar, S. D. Liles, Andre Saraiva, A. S. Dzurak, A. R. Hamilton, Dimitrie Culcer

Silicon hole quantum dots have been the subject of considerable attention thanks to their strong spin-orbit coupling enabling electrical control. The physics of silicon holes is qualitatively different from germanium holes and requires a separate theoretical description. In this work, we theoretically study the electrical control and coherence properties of silicon hole dots with different magnetic field orientations. We discuss possible experimental configurations to optimize the electric dipole spin resonance (EDSR) Rabi time, the phonon relaxation time, and the dephasing due to random telegraph noise. Our main findings are: (i) The in-plane $g$-factor is strongly influenced by the presence of the split-off band, as well as by any shear strain. The $g$-factor is a non-monotonic function of the top gate electric field, in agreement with recent experiments. This enables coherence sweet spots at specific values of the top gate field and specific magnetic field orientations. (ii) Even a small ellipticity (aspect ratios $\sim 1.2$) causes significant anisotropy in the in-plane $g$-factor, which can vary by $50\% - 100\%$ as the magnetic field is rotated in the plane. (iii) EDSR Rabi frequencies are comparable to Ge, and the ratio between the relaxation time and the EDSR Rabi time $\sim 10^5$. For an out-of-plane magnetic field the EDSR Rabi frequency is anisotropic with respect to the orientation of the driving electric field, varying by $\approx 20\%$ as the driving field is rotated in the plane. Our work aims to stimulate experiments by providing guidelines on optimizing configurations and geometries to achieve robust, fast and long-lived hole spin qubits in silicon.


Characterizing the topological properties of one-dimensional non-hermitian systems without the Berry-Zak phase. (arXiv:2309.12280v1 [quant-ph])
Didier Felbacq, Emmanuel Rousseau

A new method is proposed to predict the topological properties of one-dimensional periodic structures in wave physics, including quantum mechanics. From Bloch waves, a unique complex valued function is constructed, exhibiting poles and zeros. The sequence of poles and zeros of this function is a topological invariant that can be linked to the Berry-Zak phase. Since the characterization of the topological properties is done in the complex plane, it can easily be extended to the case of non-hermitian systems. The sequence of poles and zeros allows to predict topological phase transitions.


Model non-Hermitian topological operators without skin effect. (arXiv:2309.12310v1 [cond-mat.mes-hall])
Daniel J. Salib, Sanjib Kumar Das, Bitan Roy

We propose a general principle of constructing non-Hermitian (NH) operators for insulating and gapless topological phases in any dimension ($d$) that over an extended NH parameter regime feature real eigenvalues and zero-energy topological boundary modes, when in particular their Hermitian cousins are also topological. However, the topological zero modes disappear when the NH operators accommodate complex eigenvalues. These systems are always devoid of NH skin effects, thereby extending the realm of the bulk-boundary correspondence to NH systems in terms of solely the left or right zero-energy boundary localized eigenmodes. We showcase these general and robust outcomes for NH topological insulators in $d=1,2$ and $3$, encompassing their higher-order incarnations, as well as for NH topological Dirac, Weyl and nodal-loop semimetals. Possible realizations of proposed NH topological phases in designer materials, optical lattices and classical metamaterials are highlighted.


Realization of a minimal Kitaev chain in coupled quantum dots. (arXiv:2206.08045v2 [cond-mat.mes-hall] UPDATED)
Tom Dvir, Guanzhong Wang, Nick van Loo, Chun-Xiao Liu, Grzegorz P. Mazur, Alberto Bordin, Sebastiaan L. D. ten Haaf, Ji-Yin Wang, David van Driel, Francesco Zatelli, Xiang Li, Filip K. Malinowski, Sasa Gazibegovic, Ghada Badawy, Erik P. A. M. Bakkers, Michael Wimmer, Leo P. Kouwenhoven

Majorana bound states constitute one of the simplest examples of emergent non-Abelian excitations in condensed matter physics. A toy model proposed by Kitaev shows that such states can arise at the ends of a spinless $p$-wave superconducting chain. Practical proposals for its realization require coupling neighboring quantum dots in a chain via both electron tunneling and crossed Andreev reflection. While both processes have been observed in semiconducting nanowires and carbon nanotubes, crossed-Andreev interaction was neither easily tunable nor strong enough to induce coherent hybridization of dot states. Here we demonstrate the simultaneous presence of all necessary ingredients for an artificial Kitaev chain: two spin-polarized quantum dots in an InSb nanowire strongly coupled by both elastic co-tunneling and crossed Andreev reflection. We fine-tune this system to a sweet spot where a pair of Poor Man's Majorana states is predicted to appear. At this sweet spot, the transport characteristics satisfy the theoretical predictions for such a system, including pairwise correlation, zero charge and stability against local perturbations. While the simple system presented here can be scaled to simulate a full Kitaev chain with an emergent topological order, it can also be used imminently to explore relevant physics related to non-Abelian anyons.


Emergent generalized symmetry and maximal symmetry-topological-order. (arXiv:2212.14432v2 [cond-mat.str-el] UPDATED)
Arkya Chatterjee, Wenjie Ji, Xiao-Gang Wen

A characteristic property of a gapless liquid state is its emergent symmetry and dual symmetry, associated with the conservation laws of symmetry charges and symmetry defects respectively. These conservation laws, considered on an equal footing, can't be described simply by the representation theory of a group (or a higher group). They are best described in terms of a topological order (TO) with gappable boundary in one higher dimension; we call this the symTO of the gapless state. The symTO can thus be considered a fingerprint of the gapless state. We propose that a largely complete characterization of a gapless state, up to local-low-energy equivalence, can be obtained in terms of its maximal emergent symTO. In this paper, we review the symmetry/topological-order (Symm/TO) correspondence and propose a precise definition of maximal symTO. We discuss various examples to illustrate these ideas. We find that the 1+1D Ising critical point has a maximal symTO described by the 2+1D double-Ising topological order. We provide a derivation of this result using symmetry twists in an exactly solvable model of the Ising critical point. The critical point in the 3-state Potts model has a maximal symTO of double (6,5)-minimal-model topological order. As an example of a noninvertible symmetry in 1+1D, we study the possible gapless states of a Fibonacci anyon chain with emergent double-Fibonacci symTO. We find the Fibonacci-anyon chain without translation symmetry has a critical point with unbroken double-Fibonacci symTO. In fact, such a critical theory has a maximal symTO of double (5,4)-minimal-model topological order. We argue that, in the presence of translation symmetry, the above critical point becomes a stable gapless phase with no symmetric relevant operator.


Interplay between chiral media and perfect electromagnetic conductor plates: repulsive vs. attractive Casimir force transitions. (arXiv:2301.12870v6 [hep-th] UPDATED)
Thomas Oosthuyse, David Dudal

We determine the Casimir energies and forces in a variety of potentially experimentally viable setups, consisting of parallel plates made of perfect electromagnetic conductors (PEMCs), which generalize perfect electric conductors (PECs) and perfect magnetic conductors (PMCs), and Weyl semimetals (WSMs). Where comparison is possible, our results agree with the Casimir forces calculated elsewhere in the literature, albeit with different methods. We find a multitude of known but also new cases where repulsive Casimir forces are in principle possible, but restricting the setup to PECs combined with the aforementioned WSM geometry, results in purely attractive Casimir forces.


Higher-order topological superconductors characterized by Fermi level crossings. (arXiv:2303.07698v4 [cond-mat.mes-hall] UPDATED)
Hong Wang, Xiaoyu Zhu

We demonstrate that level crossings at the Fermi energy serve as robust indicators for higher-order topology in two-dimensional superconductors of symmetry class D. These crossings occur when the boundary condition in one direction is continuously varied from periodic to open, revealing the topological distinction between opposite edges. The associated Majorana numbers acquire nontrivial values whenever the system supports two Majorana zero modes distributed at its corners. Owing to their immunity to perturbations that break crystalline symmetries, Fermi level crossings are able to characterize a wide range of higher-order topological superconductors. By directly identifying the level-crossing points from the bulk Hamiltonian, we establish the correspondence between gapped bulk and Majorana corner states in higher-order phases. In the end, we illustrate this correspondence using two toy models. Our findings suggest that Fermi level crossings offer a possible avenue for characterizing higher-order topological superconductors in a unifying framework.


Fixed lines in a non-Hermitian Kitaev chain with spatially balanced pairing processes. (arXiv:2305.00496v2 [quant-ph] UPDATED)
Y. B. Shi, Z. Song

Exact solutions for non-Hermitian quantum many-body systems are rare but may provide valuable insights into the interplay between Hermitian and non-Hermitian components. We report our investigation of a non-Hermitian variant of a p-wave Kitaev chain by introducing staggered imbalanced pair creation and annihilation terms. We find that there exists a fixed line in the phase diagram, at which the ground state remains unchanged in the presence of non-Hermitian term under the periodic boundary condition for a finite system. This allows the constancy of the topological index in the process of varying the balance strength at arbitrary rate, exhibiting the robustness of the topology for non-Hermitian Kitaev chain under time-dependent perturbations. The underlying mechanism is investigated through the equivalent quantum spin system obtained by the Jordan-Wigner transformation for infinite chain. In addition, the exact solution shows that a resonant non-Hermitian impurity can induce a pair of zero modes in the corresponding Majorana lattice, which asymptotically approach the edge modes in the thermodynamic limit, manifesting the bulk-boundary correspondence. Numerical simulation is performed for the quench dynamics for the systems with slight deviation from the fixed line to show the stability region in time. This work reveals the interplay between the pair creation and annihilation pairing processes.


Hyperspectral photoluminescence and reflectance microscopy of 2D materials. (arXiv:2305.06945v2 [physics.optics] UPDATED)
David Tebbe (1), Marc Schütte (2), Baisali Kundu (3), Bernd Beschoten (1 and 4), Prasana K. Sahoo (3), Lutz Waldecker (1) ((1) 2nd Institute of Physics and JARA-FIT, RWTH Aachen University, Aachen, Germany, (2) 2nd Institute of Physics, RWTH Aachen University, Aachen, Germany, (3) Materials Science Center, Indian Institute of Technology, Kharagpur, West Bengal, India, (4) JARA-FIT Institute for Quantum Information, Forschungszentrum Jülich GmbH and RWTH Aachen University, Aachen, Germany)

Optical micro-spectroscopy is an invaluable tool for studying and characterizing samples ranging from classical semiconductors to low-dimensional materials and heterostructures. To date, most implementations are based on point-scanning techniques, which are flexible and reliable, but slow. Here, we describe a setup for highly parallel acquisition of hyperspectral reflection and photoluminescence microscope images using a push-broom technique. Spatial as well as spectral distortions are characterized and their digital corrections are presented. We demonstrate close-to diffraction-limited spatial imaging performance and a spectral resolution limited by the spectrograph. The capabilities of the setup are demonstrated by recording a hyperspectral photoluminescence map of a CVD-grown MoSe$_2$-WSe$_2$ lateral heterostructure, from which we extract the luminescence energies, intensities and peak widths across the interface.


Gilbert damping in metallic ferromagnets from Schwinger-Keldysh field theory: Intrinsically nonlocal and nonuniform, and made anisotropic by spin-orbit coupling. (arXiv:2306.13013v2 [cond-mat.mes-hall] UPDATED)
Felipe Reyes-Osorio, Branislav K. Nikolic

Understanding the origin of damping mechanisms in magnetization dynamics of metallic ferromagnets is a fundamental problem for nonequilibrium many-body physics of systems where quantum conduction electrons interact with localized spins assumed to be governed by the classical Landau-Lifshitz-Gilbert (LLG) equation. It is also of critical importance for applications, as damping affects energy consumption and speed of spintronic and magnonic devices. Since the 1970s, a variety of linear-response and scattering theory approaches have been developed to produce widely used formulas for computation of spatially-independent Gilbert scalar parameter as the magnitude of the Gilbert damping term in the LLG equation. The largely unexploited for this purpose Schwinger-Keldysh field theory (SKFT) offers additional possibilities, such as to rigorously derive an extended LLG equation by integrating quantum electrons out. Here we derive such equation whose Gilbert damping for metallic ferromagnets is nonlocal, i.e., dependent on all localized spins at a given time, and nonuniform, even if all localized spins are collinear and spin-orbit coupling (SOC) is absent. This is in sharp contrast to standard lore, where nonlocal damping is considered to emerge only if localized spins are noncollinear; for such situations, direct comparison on the example of magnetic domain wall shows that SKFT-derived nonlocal damping is an order of magnitude larger than the previously considered one. Switching on SOC makes such nonlocal damping anisotropic, in contrast to standard lore where SOC is usually necessary to obtain nonzero Gilbert damping scalar parameter. Our analytical formulas, with their nonlocality being more prominent in low spatial dimensions, are fully corroborated by numerically exact quantum-classical simulations.


Gain-loss-induced non-Abelian Bloch braids. (arXiv:2306.13056v2 [quant-ph] UPDATED)
B. Midya

Onsite gain-loss-induced topological braiding principle of non-Hermitian energy bands is theoretically formulated in multiband lattice models with Hermitian hopping amplitudes. Braid phase transition occurs when the gain-loss parameter is tuned across exceptional point degeneracy. Laboratory realizable effective-Hamiltonians are proposed to realize braid groups $\mathbb{B}_2$ and $\mathbb{B}_3$ of two and three bands, respectively. While $\mathbb{B}_2$ is trivially Abelian, the group $\mathbb{B}_3$ features non-Abelian braiding and energy permutation originating from the collective behavior of multiple exceptional points. Phase diagrams with respect to lattice parameters to realize braid group generators and their non-commutativity are shown. The proposed theory is conducive to synthesizing exceptional materials for applications in topological computation and information processing.


Terahertz chiral metamaterial cavities breaking time-reversal symmetry. (arXiv:2308.03195v2 [cond-mat.mes-hall] UPDATED)
Johan Andberger, Lorenzo Graziotto, Luca Sacchi, Mattias Beck, Giacomo Scalari, Jérôme Faist

We demonstrate terahertz chiral metamaterial cavities that break time-reversal symmetry by coupling the degenerate linearly polarized modes of two orthogonal sets of nano-antenna arrays using the inter-Landau level transition of a two-dimensional electron gas in a perpendicular magnetic field, realizing normalized light-matter coupling rates up to $\Omega_R/\omega_{\mathrm{cav}} = 0.78$. The deep sub-wavelength confinement and gap of the nano-antennas means that the ultra-strong coupling regime can be reached even with a very small number of carriers, making it viable to be used with a variety of 2D materials, including graphene. In addition it possesses a non-degenerate chiral ground state that can be used to study the effect of circularly polarized electromagnetic quantum fluctuations by means of weakly-perturbing magneto-transport measurements.


Influence of electronic entropy on Hellmann-Feynman forces in ab initio molecular dynamics with large temperature changes. (arXiv:2308.03963v2 [cond-mat.mtrl-sci] UPDATED)
Ming Geng, Chris E. Mohn

The Z method is a popular atomistic simulation method for determining the melting temperature where a sequence of molecular dynamics runs are carried out to target the lowest system energy where the solid always melts. Homogeneous melting at the limit of critical superheating, Th, is accompanied by a drop in temperature as kinetic energy is converted to potential energy and the equilibrium melting temperature, Tm, can be calculated directly from the liquid state. Implementation of the Z method interfaced with modern ab initio electronic structure packages use Hellmann-Feynman forces to propagate the ions in the microcanonical(NVE) ensemble where the Mermin free energy plus the ionic kinetic energy is conserved. The electronic temperature, Tel, is kept fixed along the trajectory which may introduce some spurious ion-electron interactions in MD runs with large temperature changes such as often seen in homogeneous melting and freezing processes in the NVE ensemble. We estimate systematic errors in the calculated melting temperature to choice of Tel for two main mantle components, SiO2 and CaSiO3 at high pressure. Comparison of the calculated melting temperature from runs where the Tel=Th and Tel=Tm representing reasonable upper and lower boundaries respectively to choice of Tel shows that the difference in melting temperature is 200-300 K for our two test systems. The melting temperature decreases with increasing Tel due to the increasing entropic stabilisation of the liquid and the systems melts typically about 3 times faster in MD runs with Tel = Th compared to runs where Tel = Tm. A careful choice of electron temperature in BOMD simulations where the ions are propagated using Hellmann-Feynamn forces with the Mermin free energy + the ionic kinetic energy being conserved is therefore essential for the critical evaluation of the Z method and in particular at very high temperatures.


Found 11 papers in prb
Date of feed: Fri, 22 Sep 2023 03:17:20 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)

Dynamical bulk-boundary correspondence and dynamical quantum phase transitions in higher-order topological insulators
T. Masłowski and N. Sedlmayr
Author(s): T. Masłowski and N. Sedlmayr

Dynamical quantum phase transitions occur in dynamically evolving quantum systems when nonanalyticities occur at critical times in the return rate, a dynamical analog of the free energy. This extension of the concept of phase transitions can be brought into contact with another, namely, that of topo…


[Phys. Rev. B 108, 094306] Published Thu Sep 21, 2023

Topologically protected generation of spatiotemporal optical vortices with nonlocal spatial mirror symmetry breaking metasurface
Junyi Huang, Hongliang Zhang, Bingjun Wu, Tengfeng Zhu, and Zhichao Ruan
Author(s): Junyi Huang, Hongliang Zhang, Bingjun Wu, Tengfeng Zhu, and Zhichao Ruan

Recently, nonlocal spatial mirror symmetry breaking metasurfaces have been proposed to generate spatiotemporal optical vortices (STOVs), which carry transverse orbital angular momenta. Here, we investigate the topological property of the STOV generator and show that spatial mirror symmetry breaking …


[Phys. Rev. B 108, 104106] Published Thu Sep 21, 2023

Landau-Ginzburg-Devonshire theory of the chiral phase transition in ${180}^{∘}$ domain walls of ${\mathrm{PbTiO}}_{3}$
I. Rychetsky, W. Schranz, and A. Tröster
Author(s): I. Rychetsky, W. Schranz, and A. Tröster

A new mechanism leading to a switchable Bloch-type polarization in a domain wall separating two ferroelectric domain states is proposed. A biquadratic coupling of the primary order parameter and its gradient originating from inhomogeneous electrostriction triggers the chiral phase transition (Ising-…


[Phys. Rev. B 108, 104107] Published Thu Sep 21, 2023

Jastrow wave function for the spin-1 Heisenberg chain: The string order revealed by the mapping to the classical Coulomb gas
Davide Piccioni, Christian Apostoli, Federico Becca, Guglielmo Mazzola, Alberto Parola, Sandro Sorella, and Giuseppe E. Santoro
Author(s): Davide Piccioni, Christian Apostoli, Federico Becca, Guglielmo Mazzola, Alberto Parola, Sandro Sorella, and Giuseppe E. Santoro

We show that a two-body Jastrow wave function is able to capture the ground-state properties of the $S=1$ Heisenberg chain with nearest-neighbor superexchange $J$ and single-ion anisotropy term $D$, in both the topological and large-$D$ phases (with $D/J≥0$). Here, the optimized Jastrow pseudopotent…


[Phys. Rev. B 108, 104417] Published Thu Sep 21, 2023

Variation of Landau level splitting in the Fermi level controlled Dirac metals $(\mathrm{Eu},\mathrm{Gd}){\mathrm{MnBi}}_{2}$
H. Sakai, K. Nakagawa, K. Tsuruda, J. Shiogai, K. Akiba, M. Tokunaga, S. Kimura, S. Awaji, A. Tsukazaki, H. Murakawa, and N. Hanasaki
Author(s): H. Sakai, K. Nakagawa, K. Tsuruda, J. Shiogai, K. Akiba, M. Tokunaga, S. Kimura, S. Awaji, A. Tsukazaki, H. Murakawa, and N. Hanasaki

We have experimentally studied the Landau levels near the quantum limit in the magnetic Dirac material ($\mathrm{Eu},\mathrm{Gd}){\mathrm{MnBi}}_{2}$. In this series of materials, the Fermi level is systematically controlled by substituting ${\mathrm{Eu}}^{2+}$ with ${\mathrm{Gd}}^{3+}$ while keepin…


[Phys. Rev. B 108, 115142] Published Thu Sep 21, 2023

Symmetry-enriched topological order from partially gauging symmetry-protected topologically ordered states assisted by measurements
Yabo Li (李雅博), Hiroki Sukeno (助野裕紀), Aswin Parayil Mana, Hendrik Poulsen Nautrup, and Tzu-Chieh Wei (魏子傑)
Author(s): Yabo Li (李雅博), Hiroki Sukeno (助野裕紀), Aswin Parayil Mana, Hendrik Poulsen Nautrup, and Tzu-Chieh Wei (魏子傑)

Symmetry-protected topological (SPT) phases exhibit nontrivial short-ranged entanglement protected by symmetry and cannot be adiabatically connected to trivial product states while preserving the symmetry. In contrast, intrinsic topological phases do not need ordinary symmetry to stabilize them and …


[Phys. Rev. B 108, 115144] Published Thu Sep 21, 2023

Quantized Hall conductance in graphene by nonperturbative magnetic-field-containing relativistic tight-binding approximation method
Md. Abdur Rashid, Masahiko Higuchi, and Katsuhiko Higuchi
Author(s): Md. Abdur Rashid, Masahiko Higuchi, and Katsuhiko Higuchi

In this study, we conducted a numerical investigation on the Hall conductance (${σ}_{\mathrm{Hall}}$) of graphene based on the magnetic energy band structure calculated using a nonperturbative magnetic-field-containing relativistic tight-binding approximation (MFRTB) method. The nonperturbative MFRT…


[Phys. Rev. B 108, 125132] Published Thu Sep 21, 2023

Exploring the interfacial coupling between graphene and the antiferromagnetic insulator ${\mathrm{MnPSe}}_{3}$
Xin Yi, Qiao Chen, Kexin Wang, Yuanyang Yu, Yi Yan, Xin Jiang, Chengyu Yan, and Shun Wang
Author(s): Xin Yi, Qiao Chen, Kexin Wang, Yuanyang Yu, Yi Yan, Xin Jiang, Chengyu Yan, and Shun Wang

Interfacial coupling between graphene and other two-dimensional 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 ph…


[Phys. Rev. B 108, 125427] Published Thu Sep 21, 2023

Creating a custom-designed moiré magnifying glass to probe local atomic lattice rotations in twisted bilayer graphene
Chen-Yue Hao, Jia-Qi He, Huai-Jia Qiao, Yi-Wen Liu, Ya-Ning Ren, and Lin He
Author(s): Chen-Yue Hao, Jia-Qi He, Huai-Jia Qiao, Yi-Wen Liu, Ya-Ning Ren, and Lin He

Moiré materials have risen to the forefront of physics research because of their ability to realize a disparate set of fascinating physical phenomena in these systems. Besides interesting electronic properties, the moiré pattern has been suggested to be used as a magnifying glass for local strain an…


[Phys. Rev. B 108, 125429] Published Thu Sep 21, 2023

Simulation of fermionic and bosonic critical points with emergent SO(5) symmetry
Toshihiro Sato, Zhenjiu Wang, Yuhai Liu, Disha Hou, Martin Hohenadler, Wenan Guo, and Fakher F. Assaad
Author(s): Toshihiro Sato, Zhenjiu Wang, Yuhai Liu, Disha Hou, Martin Hohenadler, Wenan Guo, and Fakher F. Assaad

We introduce a model of Dirac fermions in $2+1$ dimensions with a semimetallic, a quantum spin-Hall insulating (QSHI), and an $s$-wave superconducting (SSC) phase. The phase diagram features a multicritical point at which all three phases meet as well as a QSHI-SSC deconfined critical point. The QSH…


[Phys. Rev. B 108, L121111] Published Thu Sep 21, 2023

General scattering and electronic states in a quantum-wire network of moiré systems
Chen-Hsuan Hsu, Daniel Loss, and Jelena Klinovaja
Author(s): Chen-Hsuan Hsu, Daniel Loss, and Jelena Klinovaja

We investigate electronic states in a two-dimensional network consisting of interacting quantum wires, a model adopted for twisted bilayer systems. We construct general operators which describe various scattering processes in the system. In a twisted bilayer structure, the moiré periodicity allows f…


[Phys. Rev. B 108, L121409] Published Thu Sep 21, 2023

Found 2 papers in nat-comm


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Kapitza-resistance-like exciton dynamics in atomically flat MoSe2-WSe2 lateral heterojunction
< author missing >

Strained few-layer MoS2 with atomic copper and selectively exposed in-plane sulfur vacancies for CO2 hydrogenation to methanol
< author missing >