Fully compensated ferrimagnetism (fFIM) represents an intriguing magnetic state characterized by spin-split bands throughout the Brillouin zone, yet zero net magnetization. Unlike conventional antiferromagnets (cAFM) or altermagnets, fFIM generally does not require stringent crystallographic symmetry constraints and can exist in a wide range of space groups. This unique feature makes it a promising platform for exploring second-order nonlinear optical responses, such as the bulk photovoltaic (BPV) effect, which typically arises only in low-symmetry systems; however, the BPV effect in fFIM remains largely unexplored. In this work, we systematically investigate the generation and modulation of the BPV effect in fFIM. Using a tight-binding model on a hexagonal lattice, we elucidate the transition from cAFM to fFIM and the corresponding evolution of the BPV response under linearly polarized light. Our results reveal that fFIM exhibits richer BPV behaviors compared to cAFM. Based on spin group and magnetic group theory, we establish the nonrelativistic and relativistic BPV generation rules in hexagonal fFIM systems, encompassing systems with both weak and strong spin-orbit coupling. These findings are validated through first-principles calculations on a realistic material. This work not only advances the theoretical understanding of nonlinear photocurrents in unconventional magnetic systems but also offers new insights for designing high-performance optoelectronic devices via symmetry engineering.

Understanding and manipulating nanoscale domain wall (DW) dynamics is a central topic in magnetism and spintronics for its promising applications in logic and memory devices. In most magnetic systems, inertia affects only transient DW dynamics, while the long-time DW motion is uniquely determined by the magnitude and direction of the applied current. Here we show that this paradigm breaks down in ferrimagnets near the angular momentum compensation point. We demonstrate that a DW can propagate steadily either forward or backward under a direct current, with the direction controlled solely by the current strength. This anomalous phenomenon originates from the inertial dynamics of an internal DW collective coordinate, which behaves as a massive object evolving in a current-dependent double-well potential. By dynamically selecting between distinct stable attractors, inertia qualitatively determines the steady-state response of DWs. The predicted reversal of DW propagation direction is robust against disorders and thermal fluctuations. Our findings establish inertia as a potential control parameter for steady spin dynamics and may provide a novel strategy for controlling magnetic solitons in spintronic systems.

We investigate the finite-size effects, energy spectra, and thermodynamics of a spin-$\frac{1}{2}$ trimer, a three-sided star tetramer, and tetrahedron clusters with Heisenberg and bond-dependent Kitaev exchange. Using exact diagonalization, we compare the isotropic-exchange case with the corresponding Heisenberg-Kitaev clusters in an applied magnetic field. The Kitaev term lifts degeneracies, hybridizes states with different total-spin character, and produces nonlinear field-dependent eigenvalues associated with avoided crossings. These spectral changes generate field-driven cluster transitions, including first- and second-order ground-state transitions associated with level crossings and continuous ground-state evolution. They also redistribute finite-level Schottky weight in the magnetic heat capacity and can produce additional low-temperature heat-capacity features when the ratio $K/J$ is large. The results provide analytic cluster benchmarks for identifying how bond-dependent symmetric anisotropic exchange modifies spectra, entropy, and heat-capacity response in molecular-magnet and cluster-based spin systems. It should be noted that while these calculations provide insight into the individual Kitaev interaction, finite-size effects mean this does not fully carry over to bulk systems that exhibit quantum spin liquid behavior.

Moiré materials have attracted considerable attention over the past few years due to the rich physical phenomena they enable for classical waves through the introduction of the twist degree of freedom. In this study, we investigate optomechanical interactions in a moiré slab waveguide formed by introducing a slight mismatch between the periodicities of two ridge arrays patterned on opposite sides of a waveguide. This design configuration generates a moiré pattern that gives rise to flat bands supporting strongly localized optical and acoustic modes with highly confined energy density. The resulting periodic moiré simultaneously sustains these photonic and phononic modes with high-quality factors. We analyze the optomechanical interactions in this system by considering both the photoelastic and moving-boundaries coupling mechanisms. Numerical simulations reveal optomechanical coupling rates reaching up to 0.3 THz/nm, enabling efficient phonon-photon interactions within the waveguide. The proposed moiré waveguide platform offers substantial tunability of the optical and mechanical modes through control of the arrays mismatch that defines the moiré pattern. These results demonstrate the potential of moiré waveguide architectures for realizing high-quality optomechanical cavities with strong acoustooptical interaction.

Kagome systems are ideal platforms for exploring strongly correlated phases due to their unique electronic structure and geometric frustration. While recent solid-state realizations have uncovered a wealth of correlated states, they suffer from key limitations, including limited tunability of carrier density and interaction strength. Here, we propose an experimentally viable scheme to realize a breathing kagome moiré superlattice using a twisted trilayer of transition metal dichalcogenides (TMDs). By twisting the top and bottom layers relative to the middle layer by small angles $\theta$ and $2\theta$, respectively, we generate a kagome-like moiré potential on the central layer. Continuum model calculations reveal an isolated kagome manifold containing a flat band, Dirac points with tunable gaps, and van Hove singularities. Crucially, this platform offers unprecedented control over band structure, carrier density, and interactions, with the twist angle and electrostatic gating serving as tuning parameters. Our work opens a new route to realizing clean, tunable kagome metals and provides a versatile platform for studying strongly correlated and topological phenomena.

We analyze the uniform conductivity of a one-dimensional degenerate fermion system placed in a random disorder potential so smooth that backward scattering can be neglected. We use the nonlinear Luttinger liquid model to consider effects of both interaction and the curvature of fermionic dispersion. The finite-frequency conductivity, calculated in the lowest order of disorder potential, consists of two parts. The first one is the elastic contribution, largely independent of temperature and interaction. The second one is the inelastic contribution, strongly dependent on temperature and frequency and appearing upon the simultaneous presence of curvature, disorder, and interaction. We argue that apart from such finite-frequency conductivity, there should always remain the $\delta$-function peak of conductivity at zero frequency, whose weight is weakly dependent on the disorder.

In unsupervised learning, the training data for deep learning does not come with any labels, thus forcing the algorithm to discover hidden patterns in the data for discerning useful information. This, in principle, could be a powerful tool in identifying topological order since topology does not always manifest in obvious physical ways (e.g., topological superconductivity) for its decisive confirmation. The problem, however, is that unsupervised learning is a difficult challenge, necessitating huge computing resources, which may not always work. In the current work, we combine unsupervised and supervised learning to establish that unlabeled (simulated) data in the Majorana splitting in realistic short disordered nanowires may enable not only a distinction between ‘topological’ and ‘trivial’, but also where their crossover happens in the relevant parameter space. This may be a useful tool in identifying topology in experimental Majorana nanowires.

Using a first-principles high-throughput screening approach, we systematically investigate the two-dimensional (2D) pentagonal $P\overline{4}{2}_{1}m {\mathrm{XY}}_2$ prototype family (where X and Y are main-group elements from Group IA to VIIA and with $\mathrm{Z}=2$ formula units per primitive cell) and identify 37 previously unknown stable phases exhibiting excellent thermodynamic, elastic, and dynamic stability. Analysis of valence electron count and bonding reveals that 2D $P\overline{4}{2}_{1}m {\mathrm{XY}}_2$ phases with 10, 12, and 14 valence electrons (VEs) per chemical formula are semiconducting, whereas those with 11 and 13 VEs exhibit metallic or ferromagnetic behavior. This behavior can be rationalized using a crystal-orbital approach. Notably, 2D $P\overline{4}{2}_{1}m {\mathrm{SbB}}_2$ (11 VEs), ${\mathrm{AsB}}_2$ (11 VEs), and ${\mathrm{LiO}}_2$ (12 VEs) are predicted to be ferromagnetic semiconductors with Heyd-Scuseria-Ernzerhof band gaps of 1.06, 1.19, and 2.75 eV, respectively. These 2D pentagonal $P\overline{4}{2}_{1}m {\mathrm{XY}}_2$ phases are promising for flexible electronics due to their low in-plane Young's modulus (6–100 N/m) and large critical strain (18%–40%). Moreover, exceptional out-of-plane piezoelectricity (with coefficients $d_{36}$ ranging between 18 and 60 pm/V) is observed in 2D $P\overline{4}{2}_{1}m {\mathrm{SnBi}}_2, {\mathrm{GeBi}}_2, {\mathrm{TeGe}}_2$, and ${\mathrm{PbBi}}_2$ due to their low shear modulus and large piezoelectric stress tensors. This work not only rationalizes the structure-electronic property correlation of the 2D pentagonal $P\overline{4}{2}_{1}m {\mathrm{XY}}_2$ prototype, but also provides valuable guidance for designing multifunctional 2D materials with tunable electronic, mechanical, and piezoelectric properties.

The paucity of naturally occurring noncentrosymmetric materials is stimulating growing interest in engineered two-dimensional systems for nonlinear optical applications. Here, we show that breaking inversion symmetry in centrosymmetric bilayer ${\mathrm{Bi}}_2{\mathrm{Se}}_3$ through twisting, point-defect insertion, or the application of an external electric field unlocks rich nonlinear optical responses. In twisted bilayer ${\mathrm{Bi}}_2{\mathrm{Se}}_3$ at the first commensurate angle of $21.{78}^{\circ }$, we find peak shift- and injection-current conductivities of $-14\mathrm{nm}\mu {\mathrm{A}\mathrm{V}}^{-2}$ and $104\times {10}^8\mathrm{nm}{\mathrm{A}\mathrm{V}}^{-2}{\mathrm{s}}^{-1}$, respectively, which lie in the visible spectrum and enable efficient THz applications. The external electric field and point-defect insertion both transform the bilayer into $C_{3v}$ symmetry, with the selenium vacancy ($V_{\text{Se}}$) achieving peak shift- and injection-current conductivities of $-190\text{nm}\mu {\mathrm{A}\mathrm{V}}^{-2}$ and $-170\times {10}^8\mathrm{nm}{\mathrm{A}\mathrm{V}}^{-2}{\mathrm{s}}^{-1}$. In all three cases, the peak nonlinear optical responses are found to be comparable to those of benchmark two-dimensional (2D) materials such as GeS, and the broadband responses, including helicity-dependent current generation, make these engineered bilayers viable candidates for next-generation 2D photovoltaics.

Whether the static 0 K defect picture remains valid for strongly anharmonic, entropy-stabilized $\alpha \text{−}{\mathrm{CsPbI}}_3$ is a key open question. To address this, by combining long-time molecular dynamics with machine-learned interatomic potentials, and vibrational entropy analysis, we develop a finite-temperature thermodynamic framework that explicitly captures dynamic disorder and anharmonic lattice fluctuations. We find that the charge-transition level of $V_{\mathrm{I}}$ in α-${\mathrm{CsPbI}}_3$ lies above the conduction-band minimum, demonstrating that the vacancy behaves as an extremely shallow donor, not a deep recombination center. Short Pb-Pb dimer configurations are only rare, subpicosecond fluctuations and do not correspond to a metastable minimum on the finite-temperature free-energy landscape. Crucially, we uncover a mechanism we term entropic suppression: Strong low-frequency anharmonic fluctuations reduce the vibrational entropy available to locally contracted configurations, thereby raising their free energy at finite temperature. This vibrational-entropy-driven suppression of the dimer basin resolves the long-standing discrepancy between static deep-defect predictions and experimentally observed benign behavior. Our work establishes a thermodynamic framework for understanding defect tolerance in soft-lattice semiconductors, where vibration entropy, not configurational entropy, plays the dominant role.

Here, we investigate how crystal symmetry tailors the non-Hermitian electro-optic effect arising from the Berry curvature dipole. Specifically, we demonstrate the critical influence of the material's point group symmetry and external electric biases in shaping this effect, leading to current-induced optical gain and nonreciprocal optical responses. Through a symmetry-based analysis of the crystallographic point groups, we identify how different symmetries affect the electro-optic response, enabling the engineering of polarization-dependent optical gain without the need for gyrotropic effects. In particular, we demonstrate that the non-Hermitian electro-optic response in a broad class of crystals is characterized by linear dichroic gain. In this type of response, the eigenpolarizations that activate the gain or dissipation are linearly polarized. Depending on the point group symmetry, it is possible to achieve gain (or dissipation) for all eigenpolarizations or to observe polarization-dependent gain and dissipation. Weyl semimetals emerge as promising candidates for realizing significant non-Hermitian electro-optic effects and linear dichroic gain. We further examine practical applications by studying the reflectance of biased materials in setups involving mirrors, demonstrating how optical gain and attenuation can be controlled via symmetry and bias configurations.

Wavefront dislocations (WDs)—phase singularities observed in quasiparticle interference experiments—have been studied as real-space signatures of Berry phases in graphene-family systems. However, it has remained ambiguous whether WDs reflect the topological charge of the underlying band touchings or the pseudospin phase winding of the wave function itself. Here, we disentangle the roles of topological charge and phase winding of pseudospin texture in WD experiments by investigating various ways of the annihilation of quadratic band touchings in bilayer graphene and magneto-spin-orbit graphene systems. We demonstrate that WD evolution reflects the changes in the underlying pseudospin winding while remaining insensitive to the topological charge of the band touching itself. Our results provide a refined interpretation of WD experiments and present a solid-state proposal for engineering and observing WD evolution.

Exceptional knots and links represent a remarkable class of non-Hermitian metals in which exceptional degeneracies form knotted or linked manifolds in momentum space. Here, we report a universal construction framework for realizing exceptional knots and links with arbitrary braiding topology in three-dimensional minimal two-band non-Hermitian systems. Our approach combines braid theory with semiholomorphic polynomials to establish a direct correspondence between braid words and non-Hermitian Bloch Hamiltonians. This framework enables the realization of a broad variety of exceptional configurations, including torus knots, lemniscate knots, nonfibred knots, hyperbolic knots, and multicomponent links, within explicit tight-binding Hamiltonians. Furthermore, we demonstrate controllable topological transitions in which exceptional knots can be continuously untied through redistribution and reconnection of exceptional points, accompanied by transient exceptional chains and changes in spectral complex energy braiding. Our results establish a universal route toward programmable non-Hermitian knot topology and provide a versatile platform for exploring knotted band degeneracies and their associated physical phenomena across photonic, acoustic, mechanical, and cold-atom systems.

Resonance Raman spectroscopy is a powerful tool for probing electron–phonon coupling, phonon momentum distributions, and stacking-related spectral features in InSe. Based on first-principles calculations, we systematically investigate the single-resonance Raman (SRR) and double-resonance Raman (DRR) scattering behaviors of monolayer InSe and bilayer $\beta$- and $\epsilon$-phase InSe. For monolayer InSe, the SRR response is dominated by the hole-scattering pathway (h-path), while the out-of-plane, out-of-phase Se–In vibration near $235{\mathrm{cm}}^{-1}$ $\left({\mathrm{A}}_1^{\prime 2}\right)$ exhibits the strongest resonance enhancement. The principal DRR peaks mainly originate from near-$\mathrm{\Gamma }$ intravalley overtone scattering of the in-plane Se–In relative-vibration branch $\left({\mathrm{E}}^{\prime 2}\right)$ and exhibit weak excitation-energy dispersion, while the mixed electron–hole scattering pathways (eh- and he-paths) also make appreciable contributions. Under $4.66\mathrm{eV}$ excitation, the high-frequency broad band evolves into two components, associated with additional strong resonant optical-transition channels along the $\mathrm{\Sigma }\text{–}\mathrm{M}$ direction. For bilayer InSe, the resonance enhancement of low-frequency interlayer phonon modes in the SRR spectra provides fingerprints of the layer number. In the DRR spectra, the nearly excitation-energy-independent lower-frequency principal peak $\left({\mathrm{P}}_1\right)$ is blue-shifted by approximately $9{\mathrm{cm}}^{-1}$ relative to monolayer InSe and can serve as a layer-number indicator, whereas the broad higher-frequency peak $\left({\mathrm{P}}_3\right)$ is more sensitive to stacking order and excitation energy, with the $\epsilon$ phase expected to exhibit a more pronounced excitation-energy-induced shift than the $\beta$ phase. These results clarify the microscopic origin of resonance Raman scattering in InSe and provide a theoretical basis for characterizing its layer number, interlayer vibrations, and stacking structures.

We develop a unified perturbative framework for energy transport along a chiral quantum Hall (QH) edge coupled to a disordered, compressible strip. Treating the strip as a generic linear-response environment characterized by its retarded susceptibility ${\chi }_q^R(k,\omega )$, we obtain leading corrections to both the heat flux carried by the edge plasmon and to its spectrum. Two generic regimes emerge: (i) a gapped, local dielectric response with finite-range coupling, producing a negative correction to the quantized heat flux that scales as $T^4$ at low temperatures together with a convex cubic shift of the plasmon dispersion, and (ii) a hydrodynamic (diffusive) response with relaxation, yielding a crossover from $T^4$ to $T^{3/2}$ scaling and a change of sign in the correction. We further introduce a microscopic dipolar model in which the edge couples electrostatically to localized dipole moments inside a wide compressible strip. This long-range interaction amplifies the nonlocal dielectric back-action and generates new suppression laws, $T^3$, or even $T^2$ for smooth disorder profiles, together with a universal ratio connecting spectral curvature to thermal response. Across all regimes, the total heat flux remains quantized: The apparent deficit of the plasmon contribution reflects a reversible heat drag into the compressible strip rather than a breakdown of quantization. The framework thus provides a coherent and quantitatively plausible explanation of the “missing heat flux” anomaly and unifies the thermal and spectral signatures of QH edge dynamics.

Thouless pumping of solitons in a periodic lattice yields a quantized displacement per adiabatic cycle—an integer or fractional multiple of the lattice constant, determined by the Chern number. This quantization relies on a well-defined lattice constant. Quasiperiodic lattices, however, lack this defining scale, leaving the fate of soliton transport an open question. Here, we show that solitons can nevertheless undergo Thouless pumping in quasiperiodic lattices, but in a different form: the soliton reconstructs the local lattice potential via its density distribution, spontaneously forming an effective topological structure that induces quasiquantized pumping—the displacement per cycle is not strictly quantized, yet its long-time average converges to a Chern-determined value. This breaks the existing notion that the pumped displacement per cycle is quantized. By contrast, for solitons that only weakly modify the lattice, a critical linear band topology governs the transport but cannot enforce strict quantization; residual quasiperiodic perturbations induce nonquantized drift, destroying the quantized transport.