We study numerically the real time dynamics of lattice polarons by combining the Feynman path integral and the matrix product state (MPS) approach. By constructing and solving a flow equation, we show that the integrand, viewed as a multivariable function of polaron world line parameters, can be compressed as a low bond dimension MPS, thereby allowing for efficient evaluation of various dynamical observables. We establish the effectiveness of our method by benchmarking the calculated polaron spectral function in one dimension against available results. We further demonstrate its potential by presenting the polaron spectral function in two dimensions and simulating polaron diffusion in both one and two dimensions.

Neural quantum states have emerged as a widely used approach to the numerical study of the ground states of nonstoquastic Hamiltonians. However, existing approaches often rely on a priori knowledge of the sign structure or require a separately pretrained phase network. We introduce a modified stochastic reconfiguration method that effectively uses differing imaginary time steps to evolve the amplitude and phase. Using a larger time step for phase optimization, this method enables a simultaneous and efficient training of phase and amplitude neural networks. The efficacy of our method is demonstrated on the Heisenberg $J_1-J_2$ model.

Generalized charge pumps are topological obstructions to trivializing loops in the space of symmetric gapped Hamiltonians. We show that given mild conditions on such pumps, the associated loop has high-symmetry points that must be in distinct symmetry-protected topological (SPT) phases. To further elucidate the connection between pumps and SPTs, we focus on closed paths, “pivot loops”, defined by two Hamiltonians, where the first is unitarily evolved by the second “pivot” Hamiltonian. While such pivot loops have been studied as entanglers for SPTs, here we explore their connection to pumps. We construct families of pivot loops that pump charge for various symmetry groups, often leading to SPT phases—including dipole SPTs. Intriguingly, we find examples where nontrivial pumps do not lead to genuine SPTs but still entangle representation-SPTs (RSPTs). We use the anomaly associated with the nontrivial pump to explain the a priori “unnecessary” criticality between these RSPTs. We also find that particularly nice pivot families form circles in Hamiltonian space, which we show are equivalent to the Hamiltonians satisfying the Dolan-Grady relation—known from the study of integrable models. This additional structure allows us to derive more powerful constraints on the phase diagram. Natural examples of such circular loops arise from pivoting with the Onsager-integrable chiral clock models, containing the aforementioned RSPT example. In fact, we show that these Onsager pivots underlie general group cohomology-based pumps in one spatial dimension. Finally, we recast the above in the language of equivariant families of Hamiltonians and relate the invariants of the pump to the candidate SPTs. We also highlight how certain SPTs arise in cases where the equivariant family is labeled by spaces that are not manifolds.

We derive the Schrödinger equation for a particle confined to the surface of a normal and a binormal helical nanoribbon, obtain the quantum potentials induced by their respective curved surface geometries, and study the localized states of the particle for each ribbon. When the particle kinetic energy corresponding to the longitudinal helical direction on the ribbon satisfies a certain geometric condition, the particle localizes near the inner edge for a normal ribbon and on the central helix for a binormal ribbon. This result suggests the presence of a pseudoforce that pushes the particle transversely along the width of the ribbon. We show that this phenomenon can be interpreted as a quantum analog of the Coriolis effect, which causes a transverse deflection of a classical particle moving in a rotating frame. We invoke Ehrenfest's theorem applicable to localized states and identify the quantized angular velocities of the rotating frames for the two ribbons. If the particle is an electron, then its localization at a specific width gives rise to a Hall-like voltage difference across the ribbon's width. However, unlike in the Hall effect, its origin is not an applied magnetic field, but the ribbon's curved surface geometry. When a normal helical ribbon is mechanically flipped to a binormal configuration in a periodic fashion, it results in a periodic electron transport from the inner edge to the center, giving rise to a quantum ac voltage. This can be used for designing nanoscale electromechanical devices. Quantum transport on a helical nanoribbon can be controlled by tuning the bends and twists of its surface, suggesting diverse applications in biopolymers and nanotechnology.

We investigate the plasmonic response of single- and bilayer semi-Dirac materials under the influence of a tunable parameter that governs topological transitions via Dirac cone generation/merging and incorporating band inversion terms. For single-layer systems, we demonstrate that the emergence of Dirac cones leads to an enhanced plasmon frequency range and that the plasmonic spectrum exhibits strong anisotropy, especially for finite values of the merging parameter and vanishing inversion terms. In the bilayer configurations, we uncover a second plasmon mode whose relative phase, with respect to the first mode, can be actively controlled by rotating the upper layer, which impacts the symmetry of the charge oscillations across the layers. This tunability enables switching between in- and out-of-phase plasmonic modes, offering a route toward phase-controlled collective excitations. Our results highlight the potential of semi-Dirac systems for plasmonics and interferometric applications in next-generation optoelectronic devices.

We investigate a nonequilibrium aspect of the current-driven superconducting-normal phase transition in floating Al islands of epitaxial full-shell Al/InAs nanowires. Within a transition region discontinuous voltage jumps and hysteretic behavior of the $I\text{−}V$ characteristics are observed, associated with the destruction and recovery of the superconducting order parameter in the island. The strength of the two features varies strongly in different devices in a mutually correlated way and can be suppressed by a small magnetic field. Numerical calculation explains this behavior in terms of a tiny nonequilibrium correction to the electronic energy distribution at low energies. The experiment demonstrates a critical failure of a two-temperature nonequilibrium model of the superconductor-normal transition in floating islands of hybrid nanowire devices.

In the present study, the phase transitions of bromine have been investigated using high-pressure x-ray diffraction experiments and ab initio calculations up to 230 and 180 GPa, respectively. At pressures beyond molecular dissociation, $Immm, I4/mmm$, and $Fm\overline{3}m$ phases are found, in agreement with the structural sequence found for iodine. We find that the phase transitions are remarkably sluggish—most notably for the $Immm\text{−}I4/mmm$ transition where the two phases coexist from 105(7) to 163(10) GPa, and the transition is observed to result in a small volume discontinuity. By symmetry, these phases are directly related, and ab initio calculations show no energetic barrier between them. However, calculations of the static enthalpy landscape of the close-packed phases under pressure reveal a highly anharmonic potential energy surface, resulting in strong entropic effects when investigating the phase transitions of dissociated bromine.

We study the potential influence of the particle multi-occupations on the stability of many-body localization in the disordered Bose-Hubbard model. Within the higher-energy section of the dynamical phase diagram, we find that there is no apparent finite-size boundary drift between the thermal phase and the many-body localized regime. We substantiate this observation by introducing the Van Vleck perturbation theory into the field of many-body localization. The appropriateness of this method rests largely on the peculiar Hilbert-space structure enabled by the particles' Bose statistics. The situation is reversed in the lower-energy section of the dynamical phase diagram, where the significant finite-size boundary drift pushes the putative many-body localized regime up to the greater disorder strengths. We utilize the algebraic projection method to make a connection linking the disordered Bose-Hubbard model in the lower-energy section to an intricate disordered spin chain model. This issue of the finite-size drift could hence be analogous to what happens in the disordered Heisenberg chain. Both trends might be traced back to the particles' intrinsic or emergent single-occupancy constraint such as the spin-$1/2$, hard-core boson, or spinless fermion degrees of freedom.

Many-body localization (MBL) lends remarkable robustness to nonequilibrium phases of matter. Such phases can show topological and symmetry-breaking order in their ground and excited states, but they may also belong to an anomalous localized topological phase (ALT phase). All eigenstates in an ALT phase are trivial, in that they can be deformed to product states, but the entire Hamiltonian cannot be deformed to a trivial localized model without going through a delocalization transition. Using a correspondence between MBL phases with short-ranged entanglement and locality-preserving unitaries, called quantum cellular automata (QCA), we reduce the classification of ALT phases to that of QCA. This method extends to periodically (Floquet) and quasiperiodically driven ALT phases, and captures anomalous Floquet phases within the same framework as static phases. We considerably develop the study of the topology of QCA, allowing us to classify static and driven ALT phases in low dimensions. The QCA framework further generalizes to include symmetry-enriched ALT phases (SALT phases), which we also classify in low dimensions, and provides a large class of soluble models suitable for realization in quantum simulators. In systematizing the study of ALT phases, we both greatly extend the classification of interacting nonequilibrium systems and clarify a confusion in the literature which implicitly equates nontrivial Hamiltonians with nontrivial ground states.

First-principles-based predictions of lattice thermal conductivity (TC) from perturbation theory have achieved significant success. Usually, it only includes three-phonon (3ph) scattering processes; only recently, four-phonon (4ph) scattering processes have been found to have an impact that is comparable to 3ph scattering at medium and high temperatures in various materials, while the influence of 4ph scattering on TC at low temperatures is generally believed to be insignificant. By combining the first-principles calculations, machine-learning techniques, and Boltzmann transport equation, we find that there are unusually strong 4ph processes even in the low-frequency range of two-dimensional (2D) materials such as h-$X\mathrm{N}$ ($X=\mathrm{B}$, Al, Ga), which have a remarkable influence on the low-temperature TC. Such strong 4ph processes originate from the out-of-plane acoustic (ZA) phonon mode of 2D materials. Furthermore, we find that the intensity of 4ph scattering and thus TC can be effectively manipulated by changing the dispersion of the ZA phonon mode, which can be easily achieved through strain engineering. The present study provides distinct insights into low-temperature phonon transport and its manipulation in 2D materials.

State-of-the-art tensor networks are employed to simulate the Hamiltonian ramp in the analog-digital quantum simulation of the quantum phase transition to the quasi-long-range ordered phase of the two-dimensional square-lattice $XX$ model [T. I. Andersen et al. Nature (London) 638, 79 (2025)]. We focus on the quantum Kibble-Zurek (KZ) mechanism near the quantum critical point. Using the infinite projected entangled pair state, we simulate an infinite lattice and demonstrate the KZ scaling hypothesis for the $XX$ correlations across a wide range of ramp times. We use the time-dependent variational principle algorithm to simulate a finite $8\times 8$ lattice, similar to the one in the quantum simulation, and find that adiabatic finite-size effects dominate for longer ramp times, where the correlation length's growth with increasing ramp time saturates and the excitation energy's dependence on the ramp time crosses over to a power-law decay characteristic of adiabatic transitions. This finding contradicts the quantum simulation data where the correlation length seems to obey KZ-like power laws, although with modified exponents.

Altermagnets represent a novel class of collinear magnets characterized by alternating spin-split bands and zero net magnetization, allowing for anomalous transport phenomena without stray fields and enabling ultrafast spin dynamics. Here, through group theory analysis and first-principles calculations, we explore the layer Hall and layer spin Hall effects in two-dimensional (2D) monolayer altermagnets. Using Ca(CoN)${}_2$ as a representative example, we identify symmetry-enforced spin–layer coupling configurations that lead to a vanishing anomalous Hall conductivity due to the cancellation of oppositely signed layer-resolved contributions. In contrast, the spin Hall conductivity remains symmetry-permitted and exhibits distinct layer-dependent behavior. These effects stem from layer-locked ordinary and spin Berry curvatures, governed by the underlying spin–layer coupling. Our results provide new insights into the charge and spin transport properties of 2D layered altermagnets and pave the way for advances in altermagnetic spintronics and layertronics.

Quantum magnets offer a unique platform for exploring exotic quantum phases and quantum phase transitions through external magnetic fields. A prominent example is the field-induced Bose–Einstein condensation (BEC) of magnons near the saturation field. While this behavior has been observed in low-spin systems, its realization in high-spin, quasi-two-dimensional magnets—where multiple on-site excitations are possible—remains exceptionally rare. Here, we report thermodynamic and density functional theory results on single crystals of the honeycomb-lattice antiferromagnet ${\mathrm{K}}_4{\mathrm{MnMo}}_4{\mathrm{O}}_{15}$ with $S=\frac{5}{2}$. The system undergoes a field-induced transition to a fully polarized state at the critical field ${\mu }_0{H}_{\mathrm{s}}=6.4$ T. Our results reveal possible thermodynamic signatures of magnon BEC, $T_{\mathrm{N}}\sim {(H_{\mathrm{s}}-H)}^{2/d}$ ($d=3$), expanding the purview of BEC-driven quantum criticality to a high-spin, quasi-two-dimensional antiferromagnets with negligibly small anisotropy.

We study tunneling anisotropic magnetoresistance in single-barrier tunnel junctions consisting of an $n$-type ferromagnetic semiconductor (In,Fe)Sb electrode, an (In,Al)Sb tunnel barrier, and an $n$-type InSb electrode. We measured the current-voltage ($I\text{−}V$) characteristics in the junctions and plotted the change in tunnel resistance $R$ or $\mathrm{d}I\text{/}\mathrm{d}V$ values when an external magnetic field $\mathit{H}$ was rotated between out-of-plane and in-plane directions with respect to the crystalline axes of the (In,Fe)Sb thin films. We observe a sizeable decrease in the junction resistance when $\mathit{H}$ is rotated from the perpendicular $\left[001\right]$ direction to the in-plane $\left[110\right]$ direction, whose origin is explained by considering $\mathit{H}$ direction dependent $s\text{−}d$ scatterings and the $s$,p-d hybridized band picture of (In,Fe)Sb. Meanwhile, when $\mathit{H}$ is rotated in the film plane, we observe a twofold anisotropic change in the $\mathrm{d}I\text{/}\mathrm{d}V$ with a maximum and a minimum when $\mathit{H}$ is along the $\left[\overline{1}10\right]$ and $\left[110\right]$ crystal axes, respectively. This result reflects in-plane twofold anisotropy in the density of states of the impurity band of (In,Fe)Sb, whose origin is attributed to a possible preferential distribution of Fe atoms along the $\left[\overline{1}10\right]$ direction.

Geometric frustration has long been a subject of enduring interest in condensed matter physics. While geometric frustration traditionally focuses on magnetic systems, little attention is paid to the “frustrated superconductivity” which could arise when the superconducting interaction conflicts with the crystal symmetry. The recently discovered kagome superconductors provide a particular opportunity for studying this due to the fact that the frustrated lattice structure and the interference effect between the three sublattices can facilitate the frustrated superconducting interaction. Here, we propose a theory that supports the frustrated superconducting state, derived from the onsite $s$-wave superconducting pairing in conjunction with the nearest-neighbor pairings hopping and the unique geometrical frustrated lattice structure. In this state, whereas the mutual $2\pi /3$ difference of the superconducting pairing phase causes the sixfold modulation of the amplitude and breaks the time-reversal symmetry with $4\pi$ phase changes of the superconducting pairing as one following it around the Fermi surface, it is immune to the impurities without the impurity-induced in-gap states and produces the pronounced Hebel-Slichter peak of the nuclear spin-lattice relaxation rate below $T_c$. Notably, the theory also reveals a disorder-induced superconducting pairing transition from the frustrated superconducting state to an isotropic $s$-wave superconducting state without traversing the nodal points, recovering and explaining the behavior found in experiment. This study not only serves as a promising proposal to mediate the divergent or seemingly contradictory experimental outcomes regarding superconducting pairing symmetry, but may also pave the way for advancing investigations into the frustrated superconducting state.

The emergence of a rectified steady-state supercurrent as a response to the photoexcited current of the quasiparticles constitutes the concept of a superconducting photodiode. This phenomenon occurs in a two-dimensional thin, superconducting film with a built-in DC supercurrent, which is exposed to the circularly polarized external electromagnetic field. The flow of a Cooper-pair condensate, resulting as a second-order photoresponse in a direction transverse to the initially built-in supercurrent, represents a superconducting counterpart to the photogalvanic effect. In this paper, we examine the photodiode supercurrent by restoring gauge invariance within the mean-field BCS framework. To achieve this, we derive an impurity-sensitive BCS-interaction-induced correction to the vertex function by performing self-consistent calculations within the Keldysh Green's function technique. The resulting photodiode current can be utilized for spectroscopic analysis of typical relaxation times in superconducting films.

While universal quantum computers remain under development, analog quantum simulators offer a powerful alternative for understanding complex systems in condensed matter, chemistry, and high-energy physics. One compelling application is the characterization of real-time lattice gauge theories (LGTs). LGTs are nonperturbative tools, utilizing discretized space-time to describe gauge-invariant models. They hold immense potential for understanding fundamental physics but require enforcing local constraints analogous to electromagnetism's Gauss's law. These constraints, which arise from gauge symmetries and dictate the form of the interaction between matter and gauge fields, are a significant challenge for simulators to enforce. Implementing these constraints at the hardware level in analog simulations is crucial. This requires realizing multibody interactions between matter and gauge-field elements, enabling them to evolve together while suppressing unwanted two-body interactions that violate the gauge symmetry. In this paper, we propose and implement a parametrically activated three-qubit interaction within a circuit quantum electrodynamics architecture. We experimentally demonstrate a minimal $\text{U}\left(1\right)$ spin-$\frac{1}{2}$ model with a time evolution that intrinsically satisfies Gauss's law in the system. This design serves as the foundational block for simulating LGTs on a superconducting photonic lattice.

By combining $s$-wave superconductivity (SC) and spin-momentum-locked electronic states, topological SC (TSC) can be effectively created. Usually, this requires the candidate systems to be noncentrosymmetric so that there exists some form of antisymmetric, such as Rashba spin-orbit coupling (SOC) effect. In this article, we propose a generic mechanism for inducing chiral TSC of even Chern number in two-dimensional (2D) centrosymmetric materials with hidden spin polarization arising from two noncentrosymmetric layer sectors partnered by inversion symmetry, which enables electrically controllable fusing and braiding of Majorana edge modes. Our model calculations show that the chiral TSC can be achieved with a global SC gap when Zeeman field $Z$, inter-sector interaction $t_{\perp }$, chemical potential $\mu$, and SC pairing potential $\mathrm{\Delta }$ satisfy $Z^2>{\left(t_{\perp }\pm \mu \right)}^2+{\mathrm{\Delta }}^2$. Based on first-principles calculations, we further predict 2D bismuth oxyhalides (BiOX, $\mathrm{X}=\mathrm{I}$, Br, Cl, and F) are promising centrosymmetric TSC candidates. In addition to developing a theoretical scheme of chiral TSC in 2D centrosymmetric materials, our findings significantly expend the application of BiOX, whose fabrication techniques are already well-developed, from renewable energy to quantum computing.

The successful synthesis of bilayer borophene has stimulated interest in further research on boron-based materials. Recently, Gao $et \mathit{al}$. predicted a new bilayer kagome borophene (BK-borophene) with multiple van Hove singularities [Adv. Sci. 11, 2305059 (2024)]. The peculiar influence of van Hove singularities on material properties arouse our curiosity for in-depth research on this material. Here, we regulate the properties of BK-borophene by depositing alkali and alkaline earth metal elements on one side of it and named them as $M$-BK-borophenes. Based on first-principles calculations, we analyze their dynamic and thermodynamic stability and find only two $M$-BK-borophenes ($M=\mathrm{Mg}$, Ca) to be stable at room temperature and ambient pressure. The electronic structures of Mg- and Ca-BK-borophene show that as an electron donor, Mg and Ca change the electron distribution and electron-phonon coupling of BK-borophene, enhancing their superconductivity with stronger EPC strengths of 0.97 and 0.59, as well as superconducting transition temperatures of 29.1 and 18.7 K, which is higher than the reported bilayer borophenes with an intact bilayer boron structure. Therefore, the predicted $M$-BK-borophenes ($M$ = Mg, Ca) provide platforms for the stability, electronic property regulation, and two-dimensional superconductivity realization in BK-borophene.