Structural two-level systems (TLSs) ubiquitous in amorphous solids are dramatically sensitive to thermal cycling to about $20\mathrm{K}$ and then back to low temperature, a process upon which the excitation energy of most TLSs is significantly changed. Using Monte Carlo simulations we demonstrate that this phenomenon is not contained within the standard tunneling model, but is well explained by a model that includes an additional set of TLSs that are pseudogapped at low energies, yet possess a strong strain interaction through which they generate significant dynamical disorder upon thermal cycling. Our results provide additional support for the broad applicability of the Two-TLS model to amorphous solids at low temperatures, bringing us closer to a comprehensive understanding of the universal behavior of phonon attenuation in these materials. With regard to quantum superconducting circuits, our results suggest thermal cycling as a unique protocol to distinguish TLS noise from other noise sources. The possible relation of the Two-TLS model to ionizing radiation effects on long-time fluctuations in qubit relaxation times and on TLS scrambling is discussed.

Discovering and categorizing quantum orders in mixed many-body systems are currently one of the most important problems. The target model in this study is an extended version of the cluster model in one dimension with $Z_2\otimes Z_2$ symmetry, and we investigate the effects of decoherence applied to the ground state of the model, focusing on the symmetry aspect. By using a scheme that we propose, a strong symmetry protected topological (SPT) mixed state and double average SPT (ASPT) state are constructed through the pure gapless SPT order and the domain-wall duality. Among them, the double ASPT is categorized by coexisting orders, i.e., a strong-to-weak spontaneous symmetry breaking (SWSSB) and ASPT defined by the remaining weak and strong symmetries. We make use of the doubled Hilbert space formalism for the construction scheme. We numerically demonstrate the emergence of the two mixed SPT states and find that a phase transition occurs between them tuned by the strength of decoherence. Finally, we discuss the coexistence of SPT and SWSSB in the double SPT state from the viewpoint of symmetrically invertible property, and comment on the classification of ASPT recently proposed. Suitable multiple-decoherence channel applied to SPT states gives a broad possibility to induce rich ASPTs, possessing nontrivial internal entanglement properties from the view of doubled Hilbert space formalism.

Curvilinear geometries in magnetic nanostructures provide a unique platform for exploring the interplay among symmetry, topology, and curvature in magnetization dynamics. In this paper, we analytically study the static and dynamic properties of magnetic domain walls in biaxial magnetic nanotubes with intrinsic Dzyaloshinskii-Moriya interaction of different symmetries. We show that geometry-driven local and nonlocal interactions govern domain profiles and dynamics, enabling precise control over wall propagation and Walker breakdown field. Furthermore, the combination of bulk-type Dzyaloshinskii-Moriya interaction and curvature leads to chirality symmetry breaking and chiral breakdown in magnetic domain wall motion. These findings offer a framework for tailoring domain wall textures in cylindrical nanotubes, unlocking functionalities for advanced applications in curvilinear magnonics and data storage technologies.

The generation of time-reversal-odd spin current in metallic altermagnets has attracted considerable interest in spintronics. However, producing pure spin current in insulating materials remains both challenging and desirable, as insulating states are frequently found in antiferromagnets. Nonlinear photogalvanic effects offer a promising method for generating spin current in insulators. We here reveal that spin and charge photocurrents in altermagnets are protected by spin point group symmetry. The shift and injection current mechanisms simultaneously induce spin-momentum locking in a specific direction in altermagnets regardless of spin-orbit coupling (SOC), exhibiting pure spin current. This stands in contrast to parity-time symmetric antiferromagnets, where SOC induces a charge current alongside the spin current, thereby preventing the generation of a pure spin current. We applied our predictions using first-principles calculations to several distinct materials, including wurtzite MnTe and multiferroic ${\mathrm{BiFeO}}_3$. Additionally, we elucidated the linear-inject-current mechanism in ${\mathrm{BiFeO}}_3$ induced by SOC, which may account for the enhanced bulk photovoltaic effect in multiferroics.

Despite machine learning being widely applied to investigate phases of matter, capturing the dynamics of phase transitions is very challenging due to critical slowing down and divergent correlation lengths. Here we develop a nonstationary machine learning method to learn the critical dynamics of the phase transition through a subsampling approach in the short-time regime. Importantly, we propose a universal dynamic scaling form to determine the critical point and the static critical exponent, as well as the dynamic one which previous machine learning methods were unable to obtain. We apply the machine learning method to study the depinning phase transition of skyrmions with quench disorder, which is a typical dynamic one and faces the difficulty of measuring the order parameter directly in experiments due to the complexity of the topological structures. The critical current, static, and dynamic critical exponents are determined. The generalization of our method is also verified for different cases. Compared with the traditional method based on the finite-time dynamic scaling, the results demonstrate the effectiveness of our nonstationary machine learning method even when the critical behavior of the dynamic phase transition deviates from the standard scaling form of the order parameter. Our method has high feasibility in real experiments comparing the finite-size based method, and the measurement in the short-time regime can efficiently overcome the difficulty of critical slowing down. The method can be generally applied to investigate the equilibrium and the dynamic phase transitions in various systems, even when their dynamical equations are unknown.

This study integrates infrared absorption spectroscopy, secondary ion mass spectrometry, and first-principles theoretical modeling to investigate transition metal–hydrogen complexes in ${\mathrm{SnO}}_2$. Vibrational analysis of wagging, stretching, and combination modes, coupled with uniaxial stress experiments, identifies a family of $\text{OH}-X$ centers exhibiting stretch modes at 3223, 3258, 3261, 3272, and $3300{\mathrm{cm}}^{-1}$ (measured at 10 K). These defects are structurally analogous to interstitial hydrogen centers, characterized by $\mathrm{O}-\mathrm{H}$ bonds confined to the rutile $a\text{−}b$ plane, with adjacent Sn sites in the lattice substituted by impurities or intrinsic defects. Among these, the defect responsible for the $3261{\mathrm{cm}}^{-1}$ line is attributed to hydroxyl groups adjacent to substitutional iron atoms, $\mathrm{OH}-{\mathrm{Fe}}_{\text{Sn}}$, while the $3223{\mathrm{cm}}^{-1}$ mode is linked to $\mathrm{OH}-{\mathrm{Cr}}_{\text{Sn}}$ complexes. Additionally, a transition at $5180{\mathrm{cm}}^{-1}$ is tentatively assigned to internal electronic transitions of ${\mathrm{Ir}}^{4+}$ ions substituting ${\mathrm{Sn}}^{4+}$ in the lattice. The sensitivity of this transition to hydrogenation and annealing treatments suggests that iridium functions as a deep acceptor with a charge-state transition (${\mathrm{Ir}}^{3+}/{\mathrm{Ir}}^{4+}$) near the conduction-band minimum.

We consider time evolution of order parameters and entanglement asymmetries in the ferromagnetic phase of the transverse field Ising chain. One side of the system is prepared in a ferromagnetic ground state and the other side either in equilibrium at higher temperature or out of equilibrium. We focus on the disorder-order interface in which the order parameter attains a nonzero value, different from the ground-state one. In that region, correlations follow a universal behavior. We analytically compute the asymptotic scaling functions of the one- and two-point equal-time correlations of the order parameter and provide numerical evidence that also the non-equal-time correlations are universal. We analyze the Rényi entanglement asymmetries of subsystems and obtain a prediction that is expected to hold also in the von Neumann limit. Finally, we show that the Wigner-Yanase skew information of the order paramerter in subsystems within the interfacial region scales as their length squared. We propose a semiclassical approximation that is particularly effective close to the edge of the light cone.

Nonreciprocal critical supercurrents give rise to the superconducting diode effect (SDE) in noncentrosymmetric superconductors when time-reversal symmetry is broken. In this paper, we investigate the SDE in superconductors with vanishing spin-orbit coupling but featuring narrow bands near the Fermi energy—a characteristic particularly relevant to moiré heterostructures, such as twisted bilayer graphene. Using phenomenological Ginzburg-Landau theory and self-consistent mean-field approaches, we analyze the contributions to the SDE from both conventional band dispersion and quantum geometry. While the conventional SDE arises from the asymmetric Fermi surface, we demonstrate that the quantum metric dipole generates a band quantum-geometric contribution to the SDE, even in systems with symmetric single-particle dispersion. Notably, in the flat-band limit, where the attractive interaction strength significantly exceeds the bandwidth, the contributions from quantum geometry to the supercurrent and diode effect become dominant. Our paper elucidates the conventional and quantum-geometric origins of superconducting nonreciprocity and explores their implications for flat-band superconductors.

The local Gorini-Kossakowski-Sudarshan-Lindblad (GKSL) quantum master equation is a powerful tool for the study of open quantum many-body systems. However, its microscopic derivation applicable to many-body systems is available only in limited cases, and it has yet to be fully understood under what microscopic conditions the local GKSL equation is valid. We derive the local GKSL equation on the basis of the Lieb-Robinson bound, which provides an upper bound of the propagation of information in a broad class of quantum many-body systems. We numerically test the validity of the derived local GKSL equation for a one-dimensional tight-binding fermion chain.

Projected entangled pair states (PEPS) on finite two-dimensional lattices are a natural ansatz for representing ground states of local many-body Hamiltonians, as they inherently satisfy the boundary law of entanglement entropy. In this paper, we propose the optimization of PEPS via an improved formulation of the time-dependent variational principle (TDVP), namely the minimum-step stochastic-reconfiguration scheme recently introduced for neural quantum states. We further discuss possible numerical issues that might arise in such a sampling-based approach. In this context, we investigate the entanglement properties of random PEPS and find an entanglement phase transition. We note that on one side of this transition, we can identify positive random tensors as product states. To demonstrate the power of the framework described in this paper, we apply PEPS to study the notoriously challenging chiral spin liquids. Moreover, we exhibit our approach's capability to naturally handle long-range interactions by exploring the phase diagram of Rydberg atom arrays with long-range interactions. We further provide parallelized, easy-to-use code, allowing the straightforward application of our method to general Hamiltonians composed of local interaction terms.

We investigate the heating of silicon nanoparticles due to absorption of light at 1550 nm wavelength. We conclude that the strong temperature dependence of the absorption processes in silicon leads to a thermal runaway effect, destroying the particle once it reaches a critical temperature under intense irradiation. Our results bear relevance for recent proposals to use silicon particles for levitodynamics experiments.

Rich dielectric properties in atomic transition-metal dichalcogenides (TMDs) enhance light-matter interactions and contribute to a variety of optical phenomena. Here, the use of multilayer polymethyl methacrylate (PMMA)-${\mathrm{MoS}}_2$ hybrid structures to create a vertical stacking Fabry-Pérot (FP) cavity for studying light-matter interactions in monolayer ${\mathrm{MoS}}_2$ is carried out. The thickness of the PMMA layer enables precise control over the number of FP resonance modes within the structure. Furthermore, by inserting a monolayer of ${\mathrm{MoS}}_2$ into the cavity, the evolution of an FP cavity dispersion into that of polariton dispersion can be revealed by angle-resolved reflectance. Moreover, the light-matter interaction results in multiple perfect absorptions, with the monolayer ${\mathrm{MoS}}_2$ significantly contributing to the absorption in this system, as schematically revealed by the electric field distributions in the structure. The multiple perfect absorptions produce an unusual amount of phase singularities with topological charge pairs, whose generation, evolution, and annihilation can be controlled by adjusting cavity parameters. Our findings provide a flexible and consistent framework for optimizing light-matter interactions and supporting further studies on wavefront shaping, optical vortices, and topological variants.

Recent studies have unveiled possibilities for discovering intrinsic quantum phases that are unique to open systems, including phases with average symmetry-protected topological (ASPT) order and strong-to-weak spontaneous symmetry-breaking order in systems with global symmetry. In this work, we propose a class of phases, termed the double ASPT phase, which emerges from a nontrivial extension of these two orders. This phase is absent from prior studies and cannot exist in conventional closed systems. Using the recently developed imaginary-Lindbladian formalism, we explore the phase diagram of a one-dimensional open system with ${\mathbb{Z}}_2^{\sigma }\times {\mathbb{Z}}_2^{\tau }$ symmetry. We identify universal critical behaviors along each critical line and observe the emergence of an intermediate phase that completely breaks the ${\mathbb{Z}}_2^{\sigma }$ symmetry, leading to the formation of two triple points in the phase diagram. These two triple points are topologically distinct and connected by a domain-wall decoration duality map. Our results promote the establishment of a complete classification for quantum phases in open systems with various symmetry conditions.

In many unconventional superconductors the pairing interaction is believed to be mediated by a fluctuating order. Although this is typically taken to be magnetic in origin, the role of other fluctuating orders has recently been considered. In this work we examine the weak-coupling pairing interaction produced by a general fluctuating order, and seek to identify the leading pairing instability. For a given pairing channel, we show that the superconducting fitness with the associated static order appears prominently in the expression for the coupling constant. We consequently argue that fit gaps (for which the static order is not pair breaking) should have an attractive interaction, whereas unfit gaps (for which the static order is pair breaking) have a repulsive interaction. We propose a simple heuristic test for the tendency of a given pairing state to have an attractive interaction. We show the validity of this test in the case of pairing caused by fluctuating odd-parity and density-wave orders, and use it to probe the superconducting state generated by a fluctuating noncollinear magnetic order on the pyrochlore lattice.

Recent observations of the fractional anomalous quantum Hall effect in moiré materials have reignited the interest in fractional Chern insulators (FCIs). The chiral limit in which analytic Landau-level-like single-particle states form an “ideal” Chern band and local interactions lead to Laughlin-like FCIs at $1/3$ filling has been very useful for understanding these systems by relating them to the lowest Landau level. We show, however, that, even in the idealized chiral limit, a fluctuating quantum geometry is associated with strongly broken symmetries and a phenomenology very different from that of Landau levels. In particular, particle-hole symmetry is strongly violated and, e.g., at $2/3$ filling an emergent interaction driven Fermi liquid state with no Landau level counterpart is energetically favored. In fact, even the exact Laughlin-like zero modes at $1/3$ filling have a nonuniform density tracking the underlying quantum geometry. Switching to a Coulomb interaction, the ideal Chern band with electron filling of $1/4$ features trivial charge density wave states. Moreover, applying a particle-hole transformation reveals that the ideal Chern band with hole filling of $3/4$ supports a quantum anomalous Hall crystal with quantized Hall conductance of $e^2/h$. These phenomena have no direct lowest Landau level counterpart.

We report tunneling spectroscopy and transport measurements in superconducting Al and ferromagnetic insulator EuS bilayers. The samples display remanent spin splitting, roughly half the superconducting gap, and supercurrent transport above the average paramagnetic limit. We interpret this behavior as arising from the interplay between two characteristic length scales: the superconducting coherence length $\xi$ and the magnetic domain size $d$. By comparing experimental results to a theoretical model, we find $\xi /d\approx 10$. In this regime, spin averaging across the micromagnetic configuration can locally suppress superconductivity, resulting in percolative supercurrent flow.

Floquet time crystals are characterized by the subharmonic behavior of temporal correlation functions. Studying the paradigmatic time crystal based on the disordered Floquet quantum Ising model, we show that its temporal spin correlations are directly related to spectral characteristics and that this relation provides analytical expressions for the correlation function of finite chains, which compare favorably with numerical simulations. Specifically, we show that the disorder-averaged temporal spin correlations are proportional to the Fourier transform of the splitting distribution of the pairs of eigenvalues of the Floquet operator, which differ by $\pi$ to exponential accuracy in the chain length. We find that the splittings are well described by a log-normal distribution, implying that the temporal spin correlations are characterized by two parameters. We discuss possible implications for the phase diagram of Floquet time crystals.

We demonstrate the direction sensing of surface acoustic waves (SAWs) using a single subwavelength micropillar resonator by monitoring its displacements at multiple points on its top surface. Our findings reveal that the displacements of the micropillar depend on the direction of the SAWs. This directional dependence originates from interference of bending and longitudinal resonant modes. These modes are excited by SAWs through a rotational displacement field, where the vertical component induces longitudinal resonance and the horizontal component induces bending resonance. By selecting the appropriate micropillar geometry, the frequencies of these two modes can be aligned, enabling effective mode interference. This study enhances the fundamental understanding of the interaction between SAWs and resonators, offering a practical approach for monitoring SAWs in compact electronic systems.

Since the last century, considerable efforts have been devoted to the study of valley-degenerate narrow gap semiconductors, such as the ${\mathrm{Pb}}_{1-x}{\mathrm{Sn}}_x\mathrm{Se}$ alloy. This material possesses band edges at the $L$ points of their Brillouin zone, yielding a valley degeneracy of four. However, in (111)-oriented films, it is still not fully understood how differences between the longitudinal valley, oriented along the growth axis, and the oblique valleys, oriented at an angle with respect to that axis, appear in infrared magneto-optical spectroscopy. In this work, we report a magneto-optical study on this family of alloys, focusing on an anomaly in the interband transition of the absorption strength ratio between longitudinal and oblique valleys under a magnetic field applied along the [111] direction. Based on the Mitchell-Wallis model, we provide a theoretical fit for the experimental transmission data, which quantitatively explains the spectral shape of the data at magnetic fields as high as $35\mathrm{T}$. In particular, we attribute this anomalous absorption strength variation to the carrier density difference between the two types of valleys as well as the field-dependent multiple-beam interference or the Fabry-Pérot interference. Our analysis also allows for the extraction of the real and imaginary parts of the dielectric function.

Topological band structures interfering with moiré superstructures give rise to a plethora of emergent phenomena, which are pivotal for correlated insulating and superconducting states of twisttronics materials. While quasiperiodicity was up to now a notion mostly reserved for solid-state materials and cold atoms, we here demonstrate the capacity of conventional superconducting circuits to emulate moiré physics in charge space. With two examples, we show that Hofstadter's butterfly and the magic-angle effect are directly visible in spectroscopic transport measurements. Importantly, these features survive in the presence of harmonic trapping potentials due to parasitic linear capacitances. Our proposed platform benefits from unprecedented tuning capabilities and opens the door to probe incommensurate physics in virtually any spatial dimension.