Fifty years ago, Devaney and Wolf formulated five groundbreaking invisibility theorems describing nonradiating sources and invisible particles. From the perspective of multipole decomposition, these theorems establish the conditions on the configurations of currents and electromagnetic fields that define nonradiating sources. Although these theorems are general, they encounter limitations when applied to real sources, since it is impossible to suppress all radiated harmonics in practice. However, these limitations can be mitigated in compound particles composed of two or more components. In this paper, we extend these concepts by formulating invisibility theorems for bulk compound sources and by establishing the conditions for total invisibility from the viewpoint of multipole expansion. We demonstrate that the all multipole moments of compound invisible system can be completely suppressed for all interfering multipoles, originating from polarization and magnetization parts of current density excited within the structure. We employ an extended multipole expansion framework that explicitly separates the polarization and magnetization contributions, and discuss the resulting invisibility effects. We provide examples of totally invisible spheres and core-shell dielectric/magnetic particles with identical permittivity and permeability. Our approach offers insights into the design of nonradiating and invisible structures for photonic and metamaterial applications.

Lead halide perovskites have emerged as promising optoelectronic materials; however, concerns regarding the toxicity of lead and the instability of organic cations necessitate the development of environmentally friendly and stable alternatives. Vacancy-ordered double perovskites (VODPs) present a viable solution to this challenge. However, due to the significant computational cost, theoretical studies focusing on excitonic and polaronic properties remain underexplored for these materials, which are crucial for exploring their applications in optoelectronics. In this study, we present the electronic, optical, excitonic, and polaronic properties of a series of VODPs with the chemical formula ${\mathrm{Rb}}_2{BX}_6$ $(B=\mathrm{Si}, \mathrm{Ge}, \mathrm{Sn}, \mathrm{Pt}; X=\mathrm{Cl}, \mathrm{Br}, \mathrm{I})$ using state-of-the-art first-principles calculations. Our analysis reveals that these materials exhibit intriguing electronic and optical properties. The electronic structure calculations indicate that most compounds possess a direct band gap (except ${\mathrm{Rb}}_2{\mathrm{PtBr}}_6$ and ${\mathrm{Rb}}_2{\mathrm{PtI}}_6$), and the band-gap values computed using the $G_0{W}_0$@PBE approach, span a wide range from 0.56 to 6.12 eV. Optical properties, determined via the Bethe-Salpeter equation (BSE), indicate strong infrared to ultraviolet light absorption across most systems. Additionally, the analysis of excitonic properties shows low to moderate exciton binding energies and variable exciton lifetimes, implying higher quantum yield and conversion efficiency. Furthermore, utilizing the Feynman polaron model, polaronic parameters are evaluated, which reveal high polaron mobility for electrons $(3.33-85.11{\mathrm{cm}}^2{\mathrm{V}}^{-1}{s}^{-1})$ compared to recently studied Cs-based VODP materials. Our findings suggest that these materials exhibit favorable electronic, optical, excitonic, and polaronic characteristics, positioning them as viable candidates for a wide range of next-generation optoelectronic devices.

We report the formation of a ${\mathbb{Z}}_2$ vortex crystal in the tetrahedral antiferromagnetic order on a triangular lattice. The noncoplanar tetrahedral state consists of four sublattices with spins oriented along the faces of a tetrahedron in spin space. The long-range order characterized by a ${\mathbb{Z}}_2$ topology arises due to the Dzyaloshinskii-Moriya interaction and appears at zero temperature and without external fields. Each vortex carries a half-integer electric charge relative to the uniform background in itinerant magnets, enabling the emergence of anyonic excitations. Its magnetic excitations include magnetically active gyrotropic and breathing modes, which—under an external magnetic field—carry nontrivial Chern numbers that stabilize chiral magnon edge states.

The ability to manipulate the surface states of topological insulators using electric or magnetic fields under ambient conditions is a key step toward their integration into future electronic and optoelectronic devices. Here, we demonstrate—using cyclotron resonance measurements on a tin-doped ${\mathrm{BiSbTe}}_2\mathrm{S}$ topological insulator—that moderate magnetic fields can quantize massless surface electrons into Landau levels even at room temperature. This finding suggests that surface-state electrons can behave as long-lived quasiparticles at unexpectedly high temperatures.

While the Fe-P-C metallic glass (MG) is a classic soft magnetic material, its broader application is hindered by limited glass-forming ability (GFA), whose atomic-scale origins remain inadequately understood. Unraveling these origins necessitates a precise description of atomic interactions and a comprehensive analysis of structural evolution during vitrification. However, developing reliable interatomic potentials for this ternary alloy has been challenging due to its complex hybrid metallic-covalent bonding. In this study, a deep-potential (DP) model for the Fe-P-C system was constructed by iteratively training a neural network within an active learning framework using datasets derived from ab initio molecular dynamics (AIMD) and density functional theory (DFT). The optimized potential achieves near-DFT accuracy, with deviations in lattice constants $\le 0.05\AA$ for crystals and energy-volume equations of state within 1% for amorphous phases, thereby capturing hybrid bonding features inaccessible to empirical potentials. Large-scale molecular dynamics simulations involving 5000 atoms over nanosecond durations reveal hierarchical structural evolution of $\mathrm{F}{\mathrm{e}}_{80}{\mathrm{P}}_{13}{\mathrm{C}}_7$ during the liquid-to-glass transition. As temperature decreases, phosphorus coordination shifts from solute-solute to solute-solvent preference, while weakly covalent C–C dimers ($\sim 1.425\AA$) become kinetically trapped upon cooling. Concurrently, $\langle 0,4,4,x\rangle$ Voronoi polyhedra emerge as structural intermediaries between liquid and glass states. Analysis of medium-range order further reveals distinct aggregation-repulsion patterns among Voronoi clusters and fivefold symmetric units, underscoring a competitive interplay between chemical ordering and topological frustration. These findings confirm the applicability of DP modeling to multicomponent alloys with hybrid bonding nature, provide mechanistic insights into the glass formation process of Fe-P-C MG, and elucidate the cooperative roles of chemical and topological short-range ordering in ternary MGs.

Recent advances in topological photonics have opened up a new paradigm for robust light manipulation. Exploring dynamic control of topological photonic states is one of the key issues in this field, offering significant potential for both fundamental and applied research. Here we propose a scheme to realize tunable valley-topological plasma photonic crystals using bistable kagome superlattices in dielectric barrier discharge. We observe three types of bistable kagome superlattices (types ${\mathrm{I}}_{\pm }, \mathrm{I}{\mathrm{I}}_{\pm }$, and $\mathrm{II}{\mathrm{I}}_{\pm }$), corresponding respectively to zero, radial, and tangential displacements of the cross-point filaments. High-speed imaging reveals that these superlattices comprise three distinct sublattices, in which the spatial displacements occur within the first sublattice, while the other two undergo a ${60}^{\circ }$ rotation for the ± states. By switching the discharge on and off, we demonstrate reversible switching between a conventional dielectric photonic crystal and a plasma-based topological photonic crystal. Moreover, a dynamical control on the frequency of valley-topological edge states is achieved. Our method provides a promising route for generating tunable topological photonic states with the advantages of fast response, low cost, and wide adaptability. It paves the way for many topological applications, including the integrated photonics, signal processing, and controllable optical isolators.

The ferroelectricity origin, especially the polarization switching mechanism, is of crucial importance for the physics and application of $\mathrm{Hf}{\mathrm{O}}_2$-based ferroelectrics. However, the multiple possibilities of the polarization switching mechanism make a thorough understanding of the ferroelectricity of $\mathrm{Hf}{\mathrm{O}}_2$ still challenging. In this work, based on ab initio molecular dynamics and density functional theory calculations, polarization switching is systematically studied in ${180}^{\circ }$ domain structures with different domain widths. It is found that the polarization switching mode with O atoms not shifting through the Hf atomic planes has a lower switching electric field in the broad domains, while that with O atoms shifting through the Hf atomic planes is dominative in the narrow domains. The triggering electric field of ferroelectric $\mathrm{Hf}{\mathrm{O}}_2$ increases with the decreasing of the domain width. These results are of crucial importance for the understanding of ferroelectricity of $\mathrm{Hf}{\mathrm{O}}_2$-based ferroelectrics with different microscopic structures and the fatigue and wake-up effects under different electric fields.

We present and analyze an exactly solvable interacting fermionic pairing model, which features interactions that entangle states at momenta $\mathbf{k}$ and $-\mathbf{k}$. These interactions give rise to correlated ground states, leading to a rich phase diagram that includes superconducting, multiple metallic, and Mott-insulating phases. At finite interaction strengths, we observe the emergence of multiple many-body Fermi surfaces, which violate Luttinger's theorem and challenge the conventional Landau-Fermi liquid paradigm. A distinguishing feature of our model is that it remains quantum integrable, even with the addition of pairing interactions of various symmetries, setting it apart from the Hatsugai-Kohmoto model. Our results provide an analytically tractable framework for studying strong correlation effects that give rise to fractionalized excitations and unconventional superconductivity, offering valuable insights into a broad class of integrable many-body systems.

Thermal noise is one of the physical obstacles that constrain the achievable detection sensitivities of various detectors. Indeed, as we showed in a recent paper [Phys. Rev. B 111, 024501 (2025)], the usual Josephson threshold detector (JTD) operated in an equilibrium state can be utilized to implement a weak microwave signal, just approaching (but not arriving at) its energy quantum limit, even though its physical parameters have been optimized. In the present work, we further demonstrate numerically that the phase dynamics of a current-biased Josephson junction can be insensitive to the always-on thermal noise if the sweep rate of the biased current is significantly high. As a consequence, the JTD can be operated alternatively in a nonequilibrium state. Based on the statistical binary detection criterion, we numerically show how such a nonequilibrium JTD (NEJTD) can be utilized to implement the weak microwave signal, theoretically arriving at its energy quantum limit level. The dynamic range and photon-number resolvability of the proposed NEJTD are also discussed numerically, if it can be experimentally realized as a broadband single microwave-photon detector.

The Higgs mode, originally proposed in the context of superconductivity, corresponds to oscillations of the amplitude of the superconducting order parameter. Recent terahertz-domain optical studies have found signatures consistent with the Higgs mode, but its unambiguous detection is still challenging. We predict that the existence of the Higgs mode can be unambiguously revealed by standard measurements of the transport characteristics in microwave-irradiated asymmetric and transparent Josephson junctions. One signature of the Higgs mode in a Josephson junction is the microwave-induced enhancement of the second harmonic of the equilibrium current-phase relation (at zero dc bias voltage), whose sign differs from its expected value in the absence of the Higgs mode. As the radiation frequency is varied, this enhancement exhibits resonant behavior when the microwave frequency is tuned across the Higgs mass. The second signature that we propose is the enhancement of the second harmonic of the ac Josephson current at finite dc voltage bias, which can be probed in a customary analysis of the Shapiro steps in a microwave-irradiated junction.

We report coherent overtone Rabi oscillations of optically polarized triplet electron spins and nuclear hyperpolarization in powder samples at room temperature. The strong dependence of the single-quantum resonance on the orientation of the zero-field splitting (ZFS) interaction is overcome by coherently driving the significantly narrower overtone transition. Analytical formulas for the overtone lineshape and nutation functions for axially symmetric ZFS interactions are derived. Overtone Rabi oscillations are observed in pentacene-doped $p$-terphenyl and ${\mathrm{NV}}^{-}$ centers in microdiamonds. For the former, overtone triplet dynamic nuclear polarization using the integrated solid effect leads to ${}^1\mathrm{H}$ spin polarization of $0.183\pm 0.005\%$ at a magnetic field of 0.2 T. The ${}^1\mathrm{H}$ NMR polarization is enhanced by a factor of 2600 with respect to thermal equilibrium and reaches a large portion of the randomly oriented microcrystals.

We investigate dissipation-driven topological phase transitions in one-dimensional quantum open systems governed by the Lindblad equation with linear dissipation operators, which ensure the density matrix retains its Gaussian form throughout the dynamics. By employing the modular Hamiltonian framework, we rigorously demonstrate that the ${\mathrm{Z}}_2$ topological invariant characterizing steady states in one-dimensional class D systems is exclusively dependent on the dissipation operators, rather than the system Hamiltonian. Through a sudden quench protocol where the system evolves from the steady state of one Lindbladian to another, we reveal that topological transitions can occur at analytically predictable critical times, even when the initial and final steady states share identical topological indices. These transitions are shown, both analytically and numerically, to depend solely on dissipation parameters. Entanglement spectrum analysis demonstrates bulk-edge correspondence in nonequilibrium density matrices via coexisting single-particle gap closures (periodic boundaries) and topologically protected zero modes (open boundaries), directly underpinning the detection of dissipation-induced topology in quantum simulators.

Large negative magnetoresistance (NMR) has attracted tremendous attention for its unique performance in spin electronics. Up to now, most of the mechanisms proposed to explain NMR are only effective in limited systems. In an antiferromagnetic EuMgPb single crystal, we observed a large NMR up to −24% at 14 T, 10 K, excluding contributions from weak localization, chiral anomaly, and magnetic scattering. Supported by first-principles calculations, we propose that the deformation in the Fermi surface of the antiferromagnetic ground state, resulting from the breaking $\mathcal{P}\mathcal{T}$ symmetry under magnetic field, primarily contributes to NMR. In this way, we provide a general mechanism for NMR that is suitable for various materials in nondisordered antiferromagnetic systems.

Spin-wave excitations are fundamental to understanding the behavior of magnetic materials and hold promise for future information and communication technologies. Yet, modeling these accurately in transition-metal compounds remains challenging, starting from the self-interaction errors affecting localized and partially filled $d$ orbitals in density-functional theory (DFT) with (semi)local functionals. In this work, we compare three advanced first-principles approaches for computing magnetic exchange parameters and magnon dispersions in NiO and MnO, all based on a common $\mathrm{DFT}+U$ ground state with ab initio Hubbard $U$ values obtained from density-functional perturbation theory. Two methods extract exchange parameters directly: one via total-energy differences using the four-state mapping ($\mathrm{\Delta }E$), and the other via the magnetic force theorem (MFT) using infinitesimal spin rotations. Magnon dispersions are then obtained from a Heisenberg Hamiltonian through linear spin-wave theory (LSWT). The third approach, time-dependent density-functional perturbation theory with $U$ ($\mathrm{TDDFPT}+U$), yields magnon dispersions directly from the dynamical spin susceptibility, with exchange parameters fitted a posteriori, for comparison, via LSWT. Our results show that $\mathrm{TDDFPT}+U$ and the Heisenberg model based on $\mathrm{\Delta }E$-derived parameters align well with experimental neutron scattering data, whereas the MFT-based approach shows larger discrepancies, possibly due to some inherent approximations and limitations of the particular implementation used. This study benchmarks the accuracy of state-of-the-art first-principles techniques for spin-wave modeling and contributes to advancing reliable computational tools for the study and design of magnetic materials.

Over the past ten years, flat band or geometric superconductivity has become a major issue in condensed matter physics due to the significant technological benefits it could offer. Observations of this unconventional form of superconductivity are unfortunately still very limited, and significant efforts are being made to search for candidate materials. Most existing theoretical studies focus on systems with strictly nondispersive bands, which, from an experimental point of view, represent an extremely difficult technological constraint to achieve. It is therefore crucial to understand to what extent this constraint can be relaxed. In other words, to what extent can superconductivity in flat bands survive weak perturbations? The main objective of the present study is precisely to answer this essential question in detail.

Superconducting systems may display different types of nonequilibrium states depending on the specific constraints imposed for measurement. We probe current-voltage relations of three-dimensional superconducting films by allowing finite voltages to develop across their length. Our experiments reveal sharp features of negative differential conductance which highlight the validity of the principle of minimum entropy production at the critical current transition. We have observed dissipative states with resistances intermediate between those of superconducting and normal phases at zero applied magnetic field, indicating a phenomenon of phase coexistence under nonequilibrium conditions. The features of steady states reported here are not accessible in conventional transport experiments with current-biasing methods.

We develop a neural network approach to solve the self-consistent Bogoliubov-de Gennes equations in strongly disordered $s$-wave superconductors. The method accurately reproduces inhomogeneous gap distributions and generalizes to system sizes far larger than those used in training. It reduces computational scaling from $\mathcal{O}\left(N^6\right)$ to $\mathcal{O}\left(N^2\right)$, enabling quantitative analysis of percolation phenomena and the superconductor-insulator transition with much smaller computational efforts.

We critically examine the exchange bias (EB) effect reported in ${\mathrm{Y}}_3\mathrm{F}{\mathrm{e}}_5{\mathrm{O}}_{12}\left(\mathrm{YIG}\right)/\mathrm{G}{\mathrm{d}}_3\mathrm{G}{\mathrm{a}}_5{\mathrm{O}}_{12}/\mathrm{G}{\mathrm{d}}_3\mathrm{G}{\mathrm{a}}_5{\mathrm{O}}_{12}$ heterostructures [Kumar et al., Phys. Rev. B 103, 064421 (2021)]. We first replicated the original experimental conditions and successfully reproduced the reported results. We then examined the dependence of the EB field on YIG thickness but observed no systematic variation, which challenges the interpretation of EB as an interfacial effect. A Cross comparison using electromagnet- and superconducting magnet-based setups further showed that the EB-like signal appears only in the latter. These findings suggest that, while the EB effect reported in the original study could exist under certain conditions, it is highly susceptible to artifacts arising from trapped magnetic fields in superconducting magnet systems. Our results highlight the necessity of rigorous cross validation when evaluating EB in low-coercivity systems such as YIG.

We reply to the Comment by Kim et al. on our article [Phys. Rev. B 103, 064421 (2021)].