The discovery of Kramers nodal line metals (KNLMs) and Kramers Weyl semimetals (KWSs) has significantly expanded the range of metallic topological materials to all noncentrosymmetric crystals. However, a key characteristic of this topology—the presence of topologically protected surface states in KNLMs—remains unclear. In this work, by constructing a $C_{1v}$ symmetric KNLM model with curved Kramers nodal lines (KNLs), we show that the Fermi-arc-like surface states (FALSSs), with a ${\mathbb{Z}}_2$ topological origin, can appear on the boundary surfaces parallel to the mirror plane. These states connect two surface momenta, corresponding to the projections of two touching points on the Fermi surfaces. Notably, upon gradually breaking achiral symmetries such as mirror and roto-inversion, the KNLM phase evolves into a KWS phase, allowing the FALSSs to evolve continuously into the Fermi arc states of the KWS. Conditions for the emergence of FALSSs in KNLMs with straight KNLs are also analyzed. Through bulk-boundary correspondence, we clarify the topological nature of KNLMs.

Time quasicrystals (TQCs) represent a compelling extension of the concept of time crystals (TCs). While TCs break discrete time-translation symmetry by exhibiting a periodic response at a subharmonic of the driving frequency, TQCs display a more complex temporal order. They respond at multiple incommensurate frequencies, values that are not integer multiples of the fundamental driving frequency, resulting in quasiperiodic dynamics. In this work, we investigate the emergence of a TQC in a disordered quantum Ising chain subjected to a quasiperiodic transverse field. Using exact diagonalization, we find that the transverse magnetization exhibits quasiperiodic oscillations that persist over extended prethermal timescales before eventual decay. This indicates that the TQC exists as a long-lived, prethermal dynamical phase rather than a true equilibrium state. We further assess the robustness of this prethermal TQC against interactions and driving imperfections, confirming its stability under realistic experimental conditions. Finite-size analysis reveals that the prethermal TQC lifetime exhibits minimal dependence on system size. Additionally, we explore the emergence of TQCs in the same chain under symmetric sampling of exchange couplings. Our results demonstrate that the TQC phase is highly sensitive to both the choice of coupling distribution and the values of the driving frequencies. These findings highlight promising experimental prospects for realizing TQCs in cold atom systems and quantum simulators, providing valuable insights into their stability, dynamical properties, and potential for exploring novel nonequilibrium quantum phases.

Simultaneous driving by two periodic oscillations yields a practical technique for further engineering quantum systems. For quantum transport through mesoscopic systems driven by two strong periodic terms, a nonperturbative Floquet-based quantum master equation (QME) approach is developed using a set of dissipative time-dependent terms and the reduced density matrix of the system. In this work, we extend our previous Floquet approach for transport through quantum dots (at finite temperature and arbitrary bias) driven periodically by a single frequency. In a pedagogical way, we derive explicit time-dependent dissipative terms. Our theory begins with the derivation of the two-mode Floquet Liouville–von Neumann equation. We then explain the second-order Wangsness-Bloch-Redfield QME with a slightly modified definition of the interaction picture. Subsequently, the two-mode Shirley time-evolution formula is applied, allowing for the integration of reservoir dynamics. Consequently, the established formalism has a wide range of applications in open quantum systems driven by two modes in the weak coupling regime. The potential applications of the formalism are demonstrated through various examples.

Skyrmions, with both topological and chiral degrees of freedom, hold significant promise for future information storage technologies. However, the dynamic behaviors of both chirality and topology remain unclear, and challenges persist in the annihilation and recovery of these topologically nontrivial magnetic structures. In this study, we report the dynamic behavior of the skyrmion lattice in a microwave field using micromagnetism simulation and statistical analysis. By analyzing the time correlation functions of spin, spin chirality, and topology, we find that the dynamical responses of the three quantities to the microwave field are not synchronized. Our dynamical analysis reveals that nonlinear effects persist in the system, regardless of whether the skyrmion is annihilated. We observe frequency multiplier modes for the spin, spin chirality, and topology across all excitation frequency ranges. Notably, in the frequency range where skyrmions are annihilated, the composite mode $n{f}_0\pm f^{\prime }$ ($n$ is an integer) is more prominent for spin and spin chirality. Furthermore, the ferromagnetic state can be nearly fully restored to the skyrmion lattice if one adjusts external parameters such as the amplitude of the microwave field and the temperature. This work distinguishes chirality and topological fluctuations through dynamic statistical methods, providing a theoretical basis for the design of new spintronic devices based on chirality-topology coupling.

Recently, altermagnetic materials have become rather attractive because such materials showcase the combined advantages of ferromagnets (e.g., spin current) and antiferromagnets (e.g., a low stray field and ultrafast spin dynamics). Symmetry arguments imply that $d$-wave altermagnets may host strain-induced nonrelativistic Zeeman-type spin splittings (ZSSs), and a theoretical, numerical, and experimental justification of such phenomena are of high necessity. In the present paper, we work with collinear spin point groups (SPGs) and use a symmetry analysis to identify 15 SPGs that host strain-induced nonrelativistic ZSSs. These 15 SPGs coincide with the cases associated with $d$-wave alternating spin splittings reported in the literature. We further corroborate our analysis by first-principles numerical simulations, which indicate that a shear strain of $2\%$ creates sizable nonrelativistic ZSSs of up to 177, 100, and 102 meV in ${\mathrm{CoF}}_2, {\mathrm{LiFe}}_2{\mathrm{F}}_6$, and ${\mathrm{La}}_2{\mathrm{O}}_3{\mathrm{Mn}}_2{\mathrm{Se}}_2 d$-wave altermagnetic semiconductors, respectively. Our work suggests an alternative route toward creating spin current in altermagnets, which may be used to design altermagnetic-based spintronic devices.

A possible route to realize fault-tolerant quantum computing is to find unconventional superconductors, where superconductivity coexists with nontrivial band topology. In this work, we report such a possibility in $6R-{\mathrm{SnNbSe}}_2$ obtained by Sn intercalation into ${\mathrm{NbSe}}_2$. Rietveld refinement confirms a centrosymmetric crystal structure with space group $R\overline{3}m$. Structural, electronic, and magnetic measurements confirm the emergence of a superconducting phase with a transition temperature $T_c\approx 4$ K. The temperature dependence of the upper critical field $H_{c2}\left(T\right)$ is well described by a two-band model. Temperature-dependent magnetic penetration depth and superfluid density measurements are performed using the tunnel diode oscillator technique. Our analysis implies the mixing of nodal and nodeless order-parameter symmetry in $6R-{\mathrm{SnNbSe}}_2$. Such results are surprising for a centrosymmetric superconductor but are consistent with theoretical predictions of topological nodal-line features in ${\mathrm{SnNbSe}}_2$. Thus, $6R-{\mathrm{SnNbSe}}_2$ emerges as an interesting platform for exploring unconventional pairing mechanism in transition metal dichalcogenide superconductors.

Quasicrystals exhibit superconductivity under the unique interplay of long-range order and strong inhomogeneity, distinguishing them from both crystalline and amorphous systems. Understanding how this structural complexity affects superconducting states and phase transitions remains an important open question. Here, we unveil anomalous superconductivity in a dodecagonal quasicrystal using the attractive Hubbard model within the Bogoliubov–de Gennes framework. We show that both the gap structure and critical temperature depend on the local pattern due to inhomogeneous charge distribution and kinetic terms. This leads to unconventional phase transitions between mixed phases where superconducting and normal regions coexist, even without external fields, which we term pattern-selective superconductivity. Alongside the local superconducting transition, the tiny spectral gaps—a hallmark of quasicrystals—allow thermally excited insulating regions to turn metallic. Furthermore, superconductivity can be anomalously suppressed even under stronger attractive interactions due to the alignment of the Fermi level with a spectral gap in the fragmented Hartree-shifted spectrum. These findings, not observed in conventional crystals, amorphous systems, or previous studies of quasicrystal superconductivity, highlight the distinct role of quasicrystalline order.

Nonequilibrium quasiparticle and phonon dynamics are central to the operation of superconducting devices. Superconducting detectors, such as superconducting nanowire single-photon detectors, transition-edge sensors, or microwave kinetic inductance detectors, perform best when a large quasiparticle population is generated in response to small perturbations. Conversely, for superconducting qubits and topologically protected Majorana fermions, even relatively small quasiparticle densities can lead to significant performance degradation. Hence, ideal materials for these devices would be less susceptible to quasiparticle poisoning. However, existing models of these devices often rely on approximations and phenomenology. Therefore, they lack a rigorous description of the underlying quasiparticle and phonon dynamics that are responsible for device performance. In this article, we combine kinetic equations with density functional theory to model the nonequilibrium quasiparticle and phonon dynamics of a thin superconducting film ab initio. To demonstrate the universality of our model, we illustrate two independent example applications: (1) we develop a theoretical model describing the detection of single photons in superconducting nanowires, and (2) we calculate the energy-relaxation rate of a transmon qubit due to the presence of excess quasiparticles. Our examples demonstrate from first principles that niobium nitride is well suited to be used for single-photon detection and that tantalum transmon qubits possess reduced sensitivity to quasiparticle poisoning relative to other materials, which is likely in part responsible for their longer coherence times. In contrast to previous models of superconducting devices, our ab initio approach makes predictions of device performance without experimental input and thus can be used to accelerate progress in device development. Moreover, by considering the full-bandwidth electron-phonon coupling, our approach can incorporate strong-coupling effects. Our methods effectively integrate ab initio materials modeling with nonequilibrium theory of superconductivity to perform practical modeling of superconducting devices, providing a comprehensive approach that connects fundamental theory with device-level applications.

Ferroelastic domain walls (DWs), traditionally considered functionally restricted due to antagonistic structural order parameters, are revealed to host electrically switchable polar states through synergistic flexoelectric and biquadratic coupling mechanisms. Using large-scale molecular dynamics (MD) simulations on orthorhombic $Pnma {\mathrm{CaTiO}}_3$ (CTO) with (110)-type DWs, this study demonstrates that a thermally-driven structural phase transition within DWs is related to the reduced out-of-phase $a^{-} {\mathrm{TiO}}_6$ octahedral tilt (Glazer tilt notation $a^{-}{a}^{-}{c}^{+}$) model, activating an achiral-to-chiral polar transition. The DW structural phase transition occurs more than 300 K below the bulk transitions, and the $z$-axis $\left({\left[001\right]}_{pc}\right)$ polar component becomes switchable at temperatures above 1100 K. Electric-field-driven DW switching, mediated by octahedral tilt suppression, DW flexoelectricity and biquadratic coupling, manifests volatile, antiferroelectric-like double hysteresis loops. At room temperature, a critical field of $\sim 3.6\times {10}^4\mathrm{kV}/\mathrm{cm}$ triggers polarization reversal by suppressing octahedral tilts both in the DWs and bulk, while thermal broadening of DWs at elevated temperatures (e.g., 1000 K) reduces strain gradients and lowers the coercive field by $\sim 42\%$, enhancing switchability. These results reveal the dual role of DWs as both structural interfaces and active functional elements, offering pathways to manipulate nanoscale polar textures and engineer novel storage/memory/piezoelectric devices leveraging tunable domain-wall functionalities.

We introduce a class of models containing robust and analytically demonstrable multifractality induced by disorder correlations. Specifically, we investigate the statistics of eigenstates of disordered tight-binding models on two classes of rooted, high-dimensional graphs—trees and hypercubes—with a form of strong disorder correlations we term “radial disorder”. In this model, site energies on all sites equidistant from a chosen root are identical, while those at different distances are independent random variables (or their analog for a deterministic but incommensurate potential, a case of which is also considered). Analytical arguments, supplemented by numerical results, are used to establish that this setting hosts robust and unusual multifractal states. The distribution of multifractality, as encoded in the inverse participation ratios (IPRs), is shown to be exceptionally broad. This leads to a qualitative difference in scaling with system size between the mean and typical IPRs, with the latter the appropriate quantity to characterize the multifractality. The existence of this multifractality is shown to be underpinned by an emergent fragmentation of the graphs into effective one-dimensional chains, which themselves exhibit conventional Anderson localization. The interplay between the exponential localization of states on these chains, and the exponential growth of the number of sites with distance from the root, is the origin of the observed multifractality.

Elemental iridium presents surprising challenges for both inelastic neutron scattering (INS) and theoretical thermal transport calculations due to its high neutron absorption cross-section and strong electron-phonon interactions, respectively. Here, we overcome these challenges to measure temperature-dependent phonon dispersion curves, compare these with calculations based on density functional theory (DFT), and ultimately examine the electron-phonon limited transport behaviors of this material. Our DFT calculations demonstrate Kohn anomalies, near the $K$ point of the iridium Brillouin zone, indicating coupling between electrons and phonons. Strong electron-phonon coupling can compete with anharmonic effects to determine electrical and thermal transport behaviors and make the Kohn anomalies challenging to observe. Nonetheless, our INS measurements map these anomalies and other dispersion features over the Brillouin zone from 100 to 700 K. These measurements also uncover unexpectedly large mode specific Grüneisen parameters obtained from the temperature-dependent phonon energies, highlighting strong anharmonicity in iridium. DFT-based Boltzmann transport calculations demonstrate how anharmonicity and electron-phonon couplings determine electronic and lattice transport behaviors. Furthermore, we correlate the Kohn anomalies with calculated electron-phonon nesting functions, Fermi surfaces, and DFT-derived coupling strengths. This study provides detailed insights into the temperature-dependent mode-resolved lattice dynamics and anharmonicity, transport behavior, and electron-phonon interactions.

Dependence of x-ray magnetic circular dichroism on the experimental geometry is described by a frequency-dependent Hall vector. Using group theory, we derive a general relationship between the Hall vector and the orientation of the Néel vector $\mathbf{L}$ in altermagnets within the free valence spin (FVS) approximation, where the spin-orbit coupling of the valence electrons and their exchange interaction with the core electrons are neglected. For a given spin point group, the full $\mathbf{L}$ dependence of the Hall vector can be expressed in terms of several irreducible spectral functions. This derivation generalizes earlier results for the special cases of MnTe and ${\mathrm{MnF}}_2$. Depending on the system symmetry, x-ray magnetic circular dichroism may be present within the FVS approximation, emerge only when the FVS-neglected terms are included, or be completely forbidden.

Engineering superconductivity in pressurized topological materials is widely recognized as a promising pathway for achieving topological superconductivity. Herein, we report the pressure-tuned evolution of the structural and electronic properties of the topological semimetal ${\mathrm{VP}}_4$. Our results demonstrate that the crystal structure remains stable up to approximately 47.2 GPa, beyond which an irreversible transition to an amorphous phase takes place. Notably, the onset of amorphization is accompanied by a concurrent transition in carrier-type from holes to electrons, coupled with the emergence of superconductivity. This phenomenon provides direct evidence for pressure-induced amorphous superconductivity. With further compression, the superconducting transition temperature $T_{\mathrm{c}}$ increases monotonically, reaching a maximum of $\sim 4.9$ K under a pressure of around 76.5 GPa. Additionally, density functional theory calculations reveal that the topologically nontrivial state persists under pressure, retaining strong topological characteristics throughout the crystalline phase. Our findings establish ${\mathrm{VP}}_4$ as a distinctive platform for investigating the interplay among amorphous, superconductivity, and topology.

Thermoelectricity in superconducting tunnel junctions has always been studied under the hypothesis of equilibrium between the cold side and the thermal bath, usually in the linear regime. We define a more complete out-of-equilibrium nonlinear numerical model that reduces to the equilibrium linear model in the low-power limit. We find that the linear model does not correctly describe the behavior of superconducting tunnel junctions for parameters that are reasonable in practical experimental setups. Subsequently, we present the qualitative and quantitative differences between the models, discovering that for high power, the junction saturates and then inverts its behavior. Finally, we also clarify the difference between linear and nonlinear thermoelectricity and devise a new criterion to find nonlinear thermoelectricity in the parameter space.

Based on high-throughput screening and experimental data, we find that ${\mathrm{CeCo}}_2{\mathrm{P}}_2$ is unique in heavy-fermion materials: It has a Kondo effect at a high temperature which is nonetheless below a Co antiferromagnetic ordering temperature. This begs the question: How is the Kondo singlet formed? All other magnetic Kondo materials do not first form magnetism on the atoms whose electrons are supposed to screen the local moments. We theoretically explain these observations and show the multifaceted uniqueness of ${\mathrm{CeCo}}_2{\mathrm{P}}_2$: a playground for Kondo, magnetism, flat band, and topological physics. At high temperatures, the itinerant Co $c$ electrons of the system form nonatomic bands with a narrow bandwidth, leading to a high antiferromagnetic transition temperature. We show that the quantum geometry of the bands promotes in-plane ferromagnetism, while the weak dispersion along the $z$ direction facilitates out-of-plane antiferromagnetism. At low temperatures, we uncover a phase that manifests the coexistence of Co antiferromagnetism and the Kondo effect, linked to the $\mathcal{P}\mathcal{T}$-protected Kramers' doublets and the filling-enforced metallic nature of $c$ electrons in the antiferromagnetic phase. Subsequently, the emergence of the Kondo effect, in cooperation with glide-mirror-$z$ symmetry, creates nodal-line excitation near the Fermi energy. Our results emphasize the importance of lattice symmetry and quantum geometry, Kondo physics, and magnetism in the understanding of the correlation physics of this unique compound. We also test our theory on the structurally similar compound ${\mathrm{LaCo}}_2{\mathrm{P}}_2$ and show how we are able to understand its vastly different phase diagram.

Numerous experiments on pyrochlore oxides ${\mathrm{Pr}}_2{(\mathrm{Zr},\mathrm{Sn},\mathrm{Hf},\mathrm{Ir})}_2{\mathrm{O}}_7$ with non-Kramers ${\mathrm{Pr}}^{3+}$ ions suggest that they support a quantum spin liquid (QSL) ground state, but the precise nature of the QSL remains unclear. Quantum spin ice with dominant dipolar Ising and smaller quadrupolar transverse exchange interactions is one such candidate, but a dominant inelastic neutron scattering signal suggests that such a picture may not be consistent with experimental results. The microscopic exchange couplings of these compounds are also not known, leaving room for many possible QSL states. In this work, we use Schwinger boson mean-field theory supplemented by a projective symmetry group classification to study possible ${\mathbb{Z}}_2$ QSLs in pyrochlore magnets with dipolar-quadrupolar non-Kramers local moments. We build a mean-field phase diagram and find four QSLs in the frustrated region of parameter space that are consistent with inelastic signals observed in neutron scattering data on ${\mathrm{Pr}}_2{\mathrm{Zr}}_2{\mathrm{O}}_7$ and ${\mathrm{Pr}}_2{\mathrm{Hf}}_2{\mathrm{O}}_7$. Among these, two robust QSLs occur in the regime with dominant transverse exchange rather than Ising exchange. We then compute the static and dynamic spin structure factors for these QSL candidates, which can be used to distinguish them in neutron scattering experiments.

Momentum-dependent spin polarization exists in ferroelectric materials with strong spin-orbit coupling (SOC), which can be controlled by ferroelectric switching, promising for nonvolatile applications in spintronics. In the present work, we investigate the SOC-induced spin texture in orthorhombic $\mathrm{B}{\mathrm{i}}_6{\mathrm{O}}_9$, a recently discovered ferroelectric material with robust polarization down to the atomic limit. Utilizing first-principles calculations, we reveal the SOC-induced giant band splitting around the Γ point and notable spin texture, which can be well described by a k·p Hamiltonian with sizable Rashba parameters of ${\lambda }_R=0.65\mathrm{eV}\AA$ and Dresselhaus parameters ${\lambda }_D=-0.23\mathrm{eV}\AA$ at the conduction-band minimum. We also find that the SOC parameters can be effectively modulated by strain, resulting from band splitting and band anticrossing collectively, supported by substrate and strain-dependent calculations. The highly tunable spin texture indicates the opportunities for using $\mathrm{B}{\mathrm{i}}_6{\mathrm{O}}_9$ for the nonvolatile charge-spin conversion useful in spintronics.

Transparent oxide semiconductors face a fundamental challenge in achieving bipolar functionality due to inherent doping asymmetry. Spinel $\text{ZnG}{\text{a}}_2{\text{O}}_4$, traditionally $n$-type under oxygen-poor growth conditions, has recently been reported to exhibit $p$-type semiconductivity at elevated temperatures through the proposed formation of $\mathrm{Z}{\mathrm{n}}_{\mathrm{Ga}}$ antisite acceptors. In this work, we systematically reevaluate the feasibility of $p$-type semiconductivity in $\text{ZnG}{\text{a}}_2{\text{O}}_4$ by theoretically examining its electronic band structure and defect thermodynamics. The valence band maximum is primarily composed of deep and localized O $2p$ orbitals, severely impeding hole generation and transport. Furthermore, defect thermodynamics reveal a self-regulating compensation mechanism driven by cation antisites—$\mathrm{G}{\mathrm{a}}_{\mathrm{Zn}}$ donors and $\mathrm{Z}{\mathrm{n}}_{\mathrm{Ga}}$ acceptors. This mechanism intrinsically pins the Fermi level ($E_{\mathrm{F}}$) from mid-gap through the $n$-type region under all growth conditions. Crucially, $\mathrm{G}{\mathrm{a}}_{\mathrm{Zn}}$ donors exhibit negative formation energies across the $p$-type $E_{\mathrm{F}}$ range, triggering autocompensation that blocks extrinsic $p$-type doping. Experimental claims of high-temperature $p$-type behavior are undermined by inconsistencies in $E_{\mathrm{F}}$ measurements and unverified independently. Later proposed Zn-rich alloys $\left(\mathrm{Z}{\mathrm{n}}_{(1+2x)}\mathrm{G}{\mathrm{a}}_{2(1-x)}{\mathrm{O}}_4\right)$ with intermediate bands—intended to explain purported conductivity—are thermodynamically unstable ($\Delta H$ = −57.4 meV/atom) and exhibit unobserved sub-band-gap states. These findings confirm $\text{ZnG}{\text{a}}_2{\text{O}}_4$'s fundamental incompatibility with $p$-type functionality, necessitating rigorous experimental validation for viable $p$-type ultrawide band gap semiconductors.