We investigate charge and spin conductance, charge and spin quantum noise, along with charge and spin ${\mathrm{\Delta }}_T$ noise, as diagnostic tools to distinguish Yu-Shiba-Rusinov (YSR) states from Majorana bound states (MBS) in a one-dimensional metal/spin flipper/metal/insulator/superconductor junction. YSR states arise from magnetic impurities acting as spin flippers within a trivial $s$-wave superconducting gap, while MBS emerge in topological superconductors-often leading to ambiguity in experiments where magnetic impurities mimic zero-energy MBS signatures. By replacing the trivial superconductor with a topological one exhibiting triplet pairing (e.g., chiral-$p$ or spinless $p$-wave nanowires), we identify robust and distinguishing features of YSR and MBS states. Our analysis demonstrates that combined measurements of both charge and spin conductance, charge and spin quantum noise, and their ${\mathrm{\Delta }}_T$ noise counterparts offer unique and reliable signatures to differentiate YSR states from genuine MBS, thereby reducing false-positive interpretations in topological superconductivity experiments.

The high-pressure behavior of $\mathrm{N}{\mathrm{a}}_2\mathrm{Cu}{\mathrm{F}}_4$ is explored by powder neutron diffraction and density functional theory (DFT) calculations. A first-order phase transition is observed to take place between 2.4 and 2.9 GPa, involving a reorientation of the Jahn-Teller (JT) long axes of the $\left[\mathrm{Cu}{\mathrm{F}}_6\right]$ octahedra (and therefore the $d_{z^2}$ Cu orbitals), in agreement with our DFT calculations which suggest a transition at $\sim 2.8$ GPa. The transition can be described as being between a state of ferro-orbital order and one of A-type antiferro-orbital order, reflecting a shift in the associated electronic instability from being in the zone center to zone boundary of the first Brillouin zone of the parent structure. This change results in a decoupling of magnitude of the associated Jahn-Teller distortion of the Cu-F bond lengths from the lattice strain. This scenario is supported by our observations that the compressibility of the pretransition phase is highly anisotropic, while in the posttransition phase it becomes almost isotropic, and that we observed no further decrease of the magnitude the JT distortion up to 5 GPa, or melting of the orbital ordering in our DFT calculations up to at least 5 GPa.

We investigate ensembles of matrix product states (MPSs) generated by quantum circuit evolution followed by projection onto MPSs with a fixed bond dimension $\chi$. Specifically, we consider ensembles produced by (i) random sequential unitary circuits, (ii) random brickwork unitary circuits, and (iii) circuits involving both unitaries and projective measurements. In all cases, we analyze the spectra of the MPS transfer matrices and relate them to the spreading of mutual information in the MPS state. We show how different characteristics of the spectral density correspond to different types of circuits, revealing that these MPS ensembles retain crucial physical information on the underlying microscopic dynamics within the spectral densities of their transfer matrix. Notably, in the presence of quantum monitoring, we show the existence of a measurement-induced entanglement transition (MIPT) at finite bond dimensions, with the averaged dimension of the null space serving as the effective order parameter.

Spinel-structured compounds serve as prototypical examples of highly frustrated systems and are promising candidates for realizing the long-sought quantum spin liquid (QSL) state. However, structural disorder is inevitable in many real QSL candidates and its impact remains a topic of intense debate. In this work, we conduct comprehensive investigations on ${\mathrm{CuGa}}_2{\mathrm{O}}_4$, a spinel compound with significant structural disorder, focusing on its thermodynamic properties and spectroscopic behaviors. No long-range magnetic order is observed down to $\sim 80$ mK, as evidenced by magnetic susceptibility, specific-heat, and elastic neutron scattering measurements. More intriguingly, inelastic neutron scattering experiments reveal a broad gapless continuum of magnetic excitations around the Brillouin zone boundary, resembling the magnetic excitation spectra expected for a QSL. Nevertheless, a spin-freezing transition at $T_{\mathrm{f}}\approx 0.88$ K is identified from the cusp in the dc susceptibility curves, where a bifurcation between zero-field-cooling and field-cooling curves occurs. Furthermore, ac susceptibility measurements show a peak close to $T_{\mathrm{f}}$ at low frequency, which shifts to higher temperature with increasing frequency. These results show that ${\mathrm{CuGa}}_2{\mathrm{O}}_4$ has a spin-glass ground state, consistent with the establishment of short-range order inferred from the specific-heat measurements. Collectively, these results illustrate the crucial role of disorder in defining the excitation spectrum out of the disordered ground state. Our findings shed light onto the broader class of ${AB}_2{\mathrm{O}}_4$ spinels and advance our understanding of the spin dynamics in magnetically disordered systems.

The anisotropic propagation of particles is a fundamental transport phenomenon in solid state physics. As for crystalline semiconductors, the anisotropic charge transport opens novel designing routes for electronic devices, where the electrical or magnetic manipulation of anisotropic resistance provides essential guarantees. Motivated by the concept of anisotropic magnetoresistance, we develop an original theory on the electrically manipulatable anisotropic electroresistance. We show that piezoelectrics and ferroelectrics may showcase polarization-dependent anisotropic electrical conductivities between two perpendicular directions and the electrical conductivity anisotropy (ECA) is switchable by flipping the polarization. By symmetry analysis, we identify several point groups hosting the polarization-switchable ECA. These point groups simultaneously enable polarization-reversal induced conductivity change along specific directions, akin to the tunneling electroresistance in ferroelectric tunnel junctions. First-principles-based conductivity calculations predict that piezoelectric AlP and ferroelectric ${\mathrm{KH}}_2{\mathrm{PO}}_4$ are two good semiconductors having such exotic charge transport. Our theory can motivate the design of intriguing anisotropic electronic devices (e.g., anisotropic memristor and field effect transistor).

Symmetry plays a key role in materials hosting Dirac electrons and underpins our ability to completely flatten the Dirac cone through the tuning of physical parameters such as twisting in van der Waals heterostructures. The emergent moiré patterns in twisted bilayers at small twist angles appear, at first glance, to be independent of the initial stacking order and hence are only shifted when one layer is translated with respect to the other. However, when the twist angle is large, differences can be seen at the level of both the lattice and electronic structure in the case of twisted bilayer graphene and twisted bilayer kagome. In this work, we show that the rotational and dihedral symmetry of high-symmetry triangular bilayers is preserved for all commensurate twist angles with a sixfold symmetric twist center. Hence, we demonstrate that the exact symmetry of small twist angle systems depends upon the initial stacking of the bilayer. We further apply the principles of our method to twisted bilayer graphene with a threefold symmetric twist center to recover the results of [E. J. Mele, Phys. Rev. B 81, 161405 (2010)]. Finally, we outline how our method can be generalized to commensurate multilayer systems.

A Dirac quantum spin liquid hosts Dirac spinons, which are low-energy fractionalized neutral quasiparticles with spin 1/2 that obey the Dirac equation. Recent inelastic neutron scattering studies have revealed a cone spin continuum in ${\mathrm{YCu}}_3{\left(\mathrm{OD}\right)}_6{\mathrm{Br}}_2\left[{\mathrm{Br}}_x{\left(\mathrm{OD}\right)}_{1-x}\right]$, consistent with the convolution of two Dirac spinons. In this work, we further studied spin excitations using the inelastic neutron scattering technique. The width of low-energy spin excitations shows a linear temperature dependence, which can be explained by spinon-spinon interactions with a Dirac dispersion. Polarized neutron scattering measurements reveal that in-plane magnetic fluctuations are about 1.5 times stronger than the out-of-plane ones, suggesting the presence of Dzyaloshinskii-Moriya interaction and consistent with our theoretical modeling and simulations. Moreover, the high-energy spin excitations around 14 meV agree with the one-pair spinon-antispinon excitations in Raman studies. The real part of the dynamical susceptibility derived from the Kramers-Kronig relationship also agrees with the Knight shift measured by nuclear magnetic resonance, clearly demonstrating the negligible effects of magnetic impurities on static susceptibility. These results provide a rare example in studying quantum-spin-liquid materials where different experimental techniques can be directly compared, and they give further insights for the possible Dirac quantum spin liquid in this system.

Higher dimensions provide fertile ground for diverse topological phases and their associated localization phenomena, thanks to the rich geometric features of boundaries and defects. In this paper, we investigate non-Hermitian lattices with defects and establish a correspondence between spectral winding topology, fractal structures, and defect-localized states in arbitrary dimensions. Through analytical derivation and numerical simulations, we demonstrate that defect states emerge only when the spectral winding number exceeds a threshold determined by the defect size, which is linked to their fractal characteristics. By utilizing the Green's function, we identify amplified responses at defects under external driving fields, strengthening the physical correspondence between these topological and fractal features. Our findings offer a universal framework for understanding defect-localized states in higher-dimensional non-Hermitian systems.

We present a real-space Green's function theory and calculations of two-photon x-ray absorption (TPA). Our focus is on nonresonant $K$-shell TPA in metallic Cu, which has been observed experimentally at intense x-ray free electron laser (XFEL) sources. The theory is based on an independent particle Green's function treatment of the Kramers-Heisenberg equation and an approximation for the sum over nonresonant intermediate states in terms of a static quadrupole transition operator. XFEL effects are modeled by a partially depleted $d$ band. This approach is shown to give results for $K$-shell TPA in quantitative agreement with XFEL experiment and with a Bethe-Salpeter equation approach. We also briefly discuss many-body corrections and TPA sum rules.

We report a spin-polarized chiral fermion state in the prototypical Weyl semimetal TaAs through a combination of Shubnikov-de Haas (SdH) oscillation measurements and Density functional theory (DFT) calculations. Our first-principles calculations reveal that the Fermi pockets surrounding neighboring Weyl nodes are strongly spin-polarized with opposite chiralities, arising from the interplay between spin-orbit coupling, spatial inversion asymmetry, and the crystalline mirror symmetries of the TaAs lattice. When subjected to an external magnetic field, they are observed to undergo a distinct Zeeman splitting, appearing as pronounced SdH oscillations, whose amplitude and frequencies can significantly vary depending on the direction of the magnetic field in the mirror planes protecting the chiralities of the Weyl nodes.

Metallic altermagnets are unusual collinear magnets that feature zero net magnetization with momentum-dependent spin splitting. Here, we show that this spin splitting can induce pair density wave states even in the absence of external magnetic fields. Focusing on BCS-type attractive interactions, we find the stabilization of symmetrically distinct pair density wave states depending on the chemical potential. These states include Fulde-Ferrell and Fulde-Ferrell* states, both of which break inversion symmetry. We investigate the supercurrent properties and discover nonreciprocal supercurrents for both the Fulde-Ferrell and Fulde-Ferrell* states with distinct spatial dependencies. We propose that the supercurrent diode effect can serve as an experimental tool for distinguishing between different pair density waves in metallic altermagnets and discuss the relation to material candidates.

Disorder remains a major obstacle to realizing topological Majorana zero modes (MZMs) in superconductor-semiconductor nanowires, and we show how deep learning can be used to recover topological MZMs mitigating disorder even when the premitigation situation manifests no apparent topology. The disorder potential, as well as the scattering invariant ($T_V$) normally used to classify a device as topologically nontrivial, are not directly measurable experimentally. Additionally, the conventional signatures of MZMs have proved insufficient due to their being accidentally replicated by disorder-induced trivial states. Recent advances in machine learning provide a novel method to solve these problems, allowing the underlying topology, suppressed by disorder, to be recovered using effective mitigation procedures. In this Letter, we leverage a vision-transformer neural network trained on conductance measurements along with a covariance matrix adaptation evolution strategy (CMA-ES) optimization framework to dynamically tune gate voltages mitigating disorder effects. Unlike prior efforts that relied on indirect cost functions, our method directly optimizes $T_V$ alongside additional local density-of-states-based topological indicators. Using a lightweight neural network variant, we demonstrate that even highly disordered nanowires initially lacking any topologically nontrivial regions can be transformed into robust topological devices.

In multilayer structures, the coupling between layers gives rise to unique plasmon modes, but analytic solutions are typically available only for bilayers due to the increasing complexity as the number of layers increases. We investigate plasmons in multilayer structures, including the effects of interlayer tunneling. By introducing the Coulomb eigenvector basis for multilayer systems, which can be solved exactly using Kac-Murdock-Szegő Toeplitz matrices, we analytically derive the long-wavelength plasmon dispersions both with and without interlayer tunneling. In the $N$-layer systems, we find that, in the absence of interlayer tunneling, the out-of-phase acoustic or charge neutral plasmon modes with linear dispersions (${\omega }_{\alpha }\propto q/\sqrt{{1-cos\left(\frac{\alpha -1}{N}\pi \right)}^{\phantom{\int }}}$ for $\alpha =2,3,\cdots ,N$) exist, while the in-phase classical plasmon mode exhibits its conventional dispersion (${\omega }_1\propto \sqrt{q}$). When interlayer tunneling is present, the out-of-phase modes develop plasmon gaps that are governed by specific interband transitions, whereas the classical mode remains unaffected. These findings have broad applicability to general coupled-layer structures.

We investigate the Josephson diode effect (JDE) within quasi-2D planar systems featuring the $C_{1v}$ spin-orbit coupling (SOC) and Zeeman fields in the normal region. Our analysis is based on experimental observations conducted on ${\mathrm{MoTe}}_2$ planar Josephson junctions (JJ) subjected to out-of-plane magnetic fields. We emphasize the pivotal role of symmetry breaking in the current direction in the occurrence of JDE. Specifically, we observe the emergence of asymmetric Andreev bound states (ABSs) and $0\text{−}\pi$-like transitions with ${\phi }_0$ shifts in the current phase relations (CPRs) in systems with specific symmetry breaking induced by SOC and Zeeman fields, leading to different critical current magnitudes in opposite directions. Additionally, we explore the influence of parameters such as the strength of SOC, Zeeman field magnitude and orientation, conduction channels with different transverse momenta, and junction lengths on the JDE efficiencies. Our results indicate the potential for diverse approaches to modulate efficiencies and provide insights that can aid in the discovery of materials and design of Josephson diodes with significantly enhanced efficiency.

Motivated by recent progress in both the Josephson diode effect (JDE) in twisted bilayers of high-$T_c$ cuprate superconductors and exotic pairing function in high-$T_c$ cuprate Josephson junction, we propose to realize the field-free JDE in a $c$-axis $s$-wave/$d$-wave/$s$-wave ($s\text{−}d\text{−}s$) superconductor junction which can serve as a new phase-sensitive test of pairing symmetry in the high-temperature superconductors. The interlayer coupling between $s$- and $d$-wave superconductors can induce an effective $d+is$ superconducting state, spontaneously breaking time-reversal symmetry. The asymmetric $s\text{−}d$ interlayer couplings break the inversion symmetry. Remarkably, breaking these two symmetries leads to a ${\varphi }_0$ junction but is unnecessary to generate JDE. The emergence of the JDE in this junction depends on the $C_4$ rotational symmetry breaking. Interestingly, although breaking $C_4$ rotational symmetry does not affect either time-reversal or inversion symmetries, it can control the magnitude and polarity of diode efficiency. Furthermore, we propose observing $C_4$ symmetry-breaking controlled JDE through asymmetric Shapiro steps. Our work suggests a JDE mechanism that relies on high-temperature $d$-wave pairing, which could inversely contribute to a potential experimental method for detecting the unconventional pairing symmetry in superconductors.

Averaged observations of physical phenomena have been utilized for comprehending specific occurrences in nature; however, these may overlook the crucial characteristics of individual events, thereby leading to diverse conclusions. For example, individual wave occurrences such as superposition and interference yield markedly divergent outcomes when viewed in detail. Similarly, this study enhances the comprehensive framework of spin-orbit torque (SOT) within the hysteresis loop shift measurement by employing the average of effective magnetic fields arising from two distinct magnetic reversals. This approach facilitates the presentation of a physically descriptive SOT model, previously characterized only by single chiral domain-wall (DW) polarity qualitatively. By integrating this model with established measurement methodologies and theoretical paradigms, we advance a theoretical framework based on the magnetic DW chirality of individual DW polarities and aim to elucidate the phenomena of SOT with clarity. The anticipated outcomes include the rectification of inaccuracies in widely employed measurement methodologies and the enhancement of our comprehension of the fundamental physics, which are expected to propel advancements in next-generation spintronics materials and devices.

We investigate the geometric response of chiral superfluids when coupled to a dynamic background geometry. We find that geometry fluctuations, represented by the flexural mode, interact with the superfluid phase fluctuations (the Goldstone mode). Starting from a minimally coupled theory, we derive the equilibrium conditions for a static background defined by supercurrent, curvature, and tension, and then obtain linearized equations for the propagation of the Goldstone and flexural modes. The equations reveal distinctive chirality-dependent effects in the propagation of the flexural mode. Specifically, a background supercurrent induces a chiral drag effect, localizing flexural waves at the superfluid boundary, while background curvature introduces anisotropic corrections to the superfluid phase and group velocities, as well as a tension in the flexural mode dispersion. Furthermore, curvature couples flexural and phase modes into dressed excitations, with tilted Dirac cones along the principal curvature directions. These effects provide dynamical signatures of the formation of a chiral condensate, and can be tuned by manipulating the background geometry.

In standard studies of quantum critical points (QCPs), the dynamic critical exponent $z$ is introduced as a fundamental parameter along with global symmetries to identify universality classes. Often, the dynamic critical exponent $z$ is set to be one as the most natural choice for quantum field theory representations, which further implies emergence of higher space-time symmetries near QCPs in many condensed matter systems. In this article, we study a family of topological quantum critical points (tQCPs) where the $z=1$ quantum field theory is prohibited in a fundamental representation by a protecting symmetry, resulting in tQCPs with $z=2$. We further illustrate that when strong interactions are properly taken into account, the stable weakly interacting gapless tQCPs with $z=2$ can further make a transition to another family of gapless tQCPs with dynamic critical exponent $z=1$, without breaking the protecting symmetry. Our studies suggest that dynamic critical exponents, as well as the degrees of freedom in fermion fields, can crucially depend on interactions in topological quantum phase transitions; in tQCPs, to a large extent, they are better thought of as emergent properties.