Transport measurements on thin films of the prototypical altermagnet MnTe have yielded conflicting reports including the anomalous Hall effect (AHE) with opposite signs and resistivity independent of thickness. In this work, we resolve these discrepancies by disentangling the bulk and surface contributions to the AHE for various crystal terminations. Using first-principles calculations and symmetry-based effective models, we demonstrate that, while the bulk hosts a characteristic $g$-wave Fermi surface, metallic surface states within the bulk gap acquire ferromagnetlike spin polarization and dominate the AHE at experimentally relevant Fermi levels. Although the surface magnetization direction is determined by the terminating spin sublattice, the sign of the surface AHE follows the bulk Néel order for any fixed termination. Both bulk and surface contributions share a common symmetry origin with a small but finite out-of-plane orbital magnetization, which reverses together with the AHE upon Néel-order reversal. Furthermore, realistic interfacial chemistry sets the magnitude and overall sign of the surface AHE—a Te capping layer reverses it relative to an InP substrate interface—while the locking to the bulk Néel order persists for each interface. Our results establish how interface design can be used to control magnetotransport in altermagnetic thin films.

Hydrogen (H) is a ubiquitous and electrically active impurity in semiconductors, playing a decisive role in shaping their optical and electrical properties, particularly in wide band-gap materials such as gallium nitride (GaN). Although postgrowth activation dissociates Mg-N-H complexes, a substantial concentration of residual H remains in $p$-GaN, and its dominant atomic configurations and dynamic behavior under device-relevant operating conditions remain poorly understood. Here, we directly identify the nitrogen-vacancy-hydrogen $\left(V_{\mathrm{N}}\text{-H}\right)$ complex in $p$-GaN by combining polarization- and angle-resolved Fourier-transform infrared spectroscopy with first-principles phonon calculations. We observe a localized vibrational mode at $1727\mathrm{c}{\mathrm{m}}^{-1}$ that emerges under forward electrical bias and elevated temperature. The mode exhibits a nearly isotropic in-plane polarization response along with a pronounced out-of-plane component. The key experimental vibrational characteristics, including peak position, polarization dependence, and angle variation, are in good agreement with the first-principles calculations, providing a consistent vibrational fingerprint that supports the assignment of the mode to a $V_{\mathrm{N}}\text{-H}$ configuration. Building on this identification, we further propose a physically grounded kinetic picture in which electron injection under forward bias enables H released from the GaN lattice to participate in $V_{\mathrm{N}}\text{-H}$ formation. These findings resolve a long-standing question regarding residual H in $p$-GaN and offer critical insight into both H-related defect physics and device degradation mechanisms, with broad implications for the reliability of GaN-based electronic and optoelectronic devices.

We analyze the effects of electron-electron and electron-phonon interactions in the dynamics of a system of two or three electrons that can be trapped to a localized state and detrapped to extended band states of a quantum dot using a simple model in which the valence and conduction bands of the quantum dot are modeled by two single-particle energy levels and the trap is described by one single-particle level within the band gap. In spite of its simplicity the time dependent problem has no analytical solution but a numerically exact one can be found at a relatively low computational cost. Within this model, we study the time evolution of the electron occupancies of conduction and valence bands and the trap state, as well as the statistical factors influencing light emission of different energies. In most of the analyzed cases, the system dynamics has a very short transient determined by the hopping parameters, that can be of tens of femtoseconds, followed by a quasistationary regime in which the electron occupancies either oscillate periodically around their time-averaged values or remain nearly constant. We find signatures of strong electronic correlations in the electronic motion for negative values of the effective electron-electron Coulomb interaction that are not translated to the statistical factors for light emission. These factors always show fast oscillations associated to electrons hopping back and forth from the conduction band to the trap, irrespective of the motion of the valence band electrons. Our calculations show that light emission of different energies is always possible except in the special cases in which the valence band is initially filled with two electrons. In these cases the valence band can lose and recover electrons periodically but exciton emission is negligible at any time. We use this fact to attempt to give a possible explanation for the increase in the intensity of exciton emission with the concomitant decrease in the intensity of the green emission lines upon continuous illumination with ultraviolet radiation, experimentally observed for ZnO nanoparticles suspended in an alcohol.

Moiré phonons describe collective vibrations of a moiré superlattice produced by long-wavelength relative displacements of the constituent layers. Despite coming from the backfolding of the acoustic phonons of the individual layers, many of these modes become infrared active when the system is doped. We illustrate this effect by a direct calculation of the optical absorption of twisted bilayer graphene around different twist angles, including the magic angle. Several modes—including the acousticlike phason—acquire a dipole moment via interband matrix elements of the electron-phonon coupling (EPC) when the flat band is filled or emptied, giving rise to resonances in the optical conductivity within the single-electron gap that are strongly affected by relaxation. The phason in particular gains a charge that equals the amount of electrons per moiré cell added to or removed from neutrality. Geometrically, this can be understood as the topological quantization of a sliding Chern number. The charged phason yields a Drude-like conductivity with an effective mass that increases with lattice relaxation. Our findings are testable via THz spectroscopy, and provide an experimental knob to characterize EPC strength and disorder in moiré materials at small twist angles.

Monolayer transition metal dichalcogenides (TMDs) are characterized by relatively large carrier effective masses and suppressed screening of the Coulomb interaction, which substantially enhances the correlation effects in these structures. The direct band gap enables effective optical probing of these correlations. Here, we present an experimental observation of Wigner crystallization in monolayer ${\mathrm{WSe}}_2$ probed by the measurement of the exciton diffraction from the Wigner crystal (WC) periodic potential. We observe the formation of the WC phase in the absence of external magnetic fields at temperatures $T<25\mathrm{K}$ and carrier concentrations $n$ $<2\times {10}^{11}{\mathrm{cm}}^{-2}$. The direct observation of the exciton diffraction is enabled by the strong exciton longitudinal-transverse splitting induced by the long-range intervalley exchange interaction, leading to the large detuning between the main exciton peak and the first diffraction peak. Our findings highlight that the valley degree of freedom of charge carriers in TMDs facilitates optical probing of correlated electron phases in these structures.

Fermi's golden rule, which describes the transition rates between two electronic levels under external stimulations, is used ubiquitously in different fields of physics. The original Fermi's golden rule was derived from perturbative time-dependent Schrödinger's equation without the direct contribution by decoherence effect. However, as a result of recent developments in quantum computing and ultrafast carrier dynamics, decoherence has become a prominent topic in fundamental research. Here, by using nonadiabatic molecular dynamics, which goes beyond the time-dependent Schrödinger's equation by introducing decoherence, we study the effect of decoherence on Fermi's golden rule for the fixed basis and the adiabatic basis, respectively. We find that when the decoherence time becomes short, there is a significant deviation from Fermi's golden rule for both bases. By using monolayer ${\mathrm{WS}}_2$ as an example, we investigate the decoherence effect in the carrier transitions induced by the electron-phonon coupling with first-principles method.

Electrical detection of magnetization dynamics in magnetic insulators underpins both fundamental studies of magnon transport and the development of low-loss magnonic devices. In heavy-metal/magnetic-insulator heterostructures, spin pumping and spin-torque ferromagnetic resonance (ST-FMR) are widely used for this purpose and are often treated separately in different measurement geometries. In practice, the competition between these two effects gives rise to electrical voltage signals of opposite signs, which can lead to ambiguous interpretations of the underlying physics. Here, we show how to disambiguate their respective contributions and provide a framework for interpreting experiments involving microwave excitation of magnetic insulators and detection of magnetization dynamics via spin-charge conversion in heavy metals. We systematically investigate spin pumping and ST-FMR in nonlocal and local devices using Pt-capped thin films of thulium and bismuth-yttrium iron garnets. We show how spin-wave character, magnetic dissipation, magnetic field orientation and device geometry govern the sign and magnitude of the resulting signals. In several cases, the voltage generated by microwave excitation changes sign as the magnetization is rotated from out-of-plane to in-plane. We disentangle a contribution due to spin pumping, induced by exponentially decaying propagating spin waves, and a weakly distance-dependent contribution from ST-FMR, remotely induced by inductive coupling. We show that both the spin-wave excitation profile across the film thickness and magnetic damping largely determine which of the two contributions dominates. Hence, the sign of the electrical signal cannot be uniquely assigned to the chirality of the magnon modes. Our results resolve a key ambiguity in interpreting electrical measurements of magnetization dynamics in insulators, and establish a unified framework for understanding inverse spin Hall voltage generation in magnonic devices.

Two-dimensional altermagnets (AMs) with tunable electronic and topological properties offer promising opportunities for next-generation spintronic and optoelectronic applications. Here, we predict that monolayer VO (ML-VO) is a two-dimensional AM semiconductor with collinear magnetic ordering and $d$-wave symmetry. In its pristine structure, there are two valleys characterized by spin-valley-lattice coupling at high-symmetry points in the Brillouin zone, leading to valley-selective absorption of linearly polarized light and pronounced linear dichroism. Strain engineering provides an effective method to manipulate a phase transition: Uniaxial strain induces valley polarization, whereas biaxial strain drives a topological phase transition from a gapped state to gapless phases featuring pairs of spin-polarized Weyl points emerging along distinct momentum directions. This transition is accompanied by the suppression of linear dichroism and the emergence of universal optical absorbance, which we demonstrate using a low-energy $k·p$ model. Moreover, we identify a critical regime hosting semi-Weyl points with linear dispersion along one direction and quadratic dispersion along the other direction. Our results reveal that ML-VO is an AM and demonstrate that it provides a promising platform for exploring optical responses and strain-induced phase transitions in two-dimensional altermagnets.

Topological insulators (TIs) constitute a unique class of quantum materials owing to their topology-protected electron states. While pressure is an effective way to induce superconductivity in TIs, superconductivity often appears after phase transition or structural disorder. Therefore, identifying systems in which superconductivity emerges at relatively low-pressure regions within a well-defined topological structure is desirable. In this work, it was demonstrated that ${\mathrm{PbBi}}_6{\mathrm{Te}}_{10}$ undergoes two structural transitions from $R\text{−}3m$ to $C2/m$ and subsequently to disordered $Im\text{−}3m$ structure under high pressure. Superconductivity emerged at 0.9 GPa and reached a maximum transition temperature of 8.8 K at 4.2 GPa within the initial structural phase, forming a dome-shaped phase diagram. First-principles calculations revealed that the bands remained topologically nontrivial under 4.0 GPa. These results establish ${\mathrm{PbBi}}_6{\mathrm{Te}}_{10}$ as a platform for exploring the interplay between pressure-induced superconductivity and nontrivial topological states.

Minimal Kitaev chains host Majorana quasiparticles, which, although not topologically protected, exhibit spatial nonlocality and hence are expected to be useful for quantum information tasks. In this work, we consider two- and three-site Kitaev chains and investigate the dynamics of bipartite and multipartite entanglement by means of concurrence and geometric measure of entanglement. In two-site Kitaev chains, we find that maximally entangled states can robustly emerge, with their stability and periodicity highly controllable by the interplay between the superconducting pair potential and the on-site energies. At the finely tuned sweet spot, where Majorana quasiparticles appear, the system exhibits oscillations between separable and entangled states, whereas detuning introduces tunable valleys in the entanglement dynamics. Extending to the three-site Kitaev chain, we uncover rich bipartite and multipartite entanglement by generalizing the concepts of concurrence and geometric measure of entanglement. At the sweet spot, the Majorana quasiparticles emerging at the edges suppress concurrence between the edges, while a finite detuning is able to restore it. Depending on the initial state, the three-site Kitaev chain can dynamically generate either a maximally entangled Greenberger-Horne-Zeilinger state or an imperfect W-type state exhibiting multipartite entanglement, although a (maximally entangled) pure W state cannot be realized due to parity constraints. Our results provide a resource for generating and characterizing highly entangled states in minimal Kitaev chains, with potential relevance for quantum applications.

Ferroelectric materials are key to energy-efficient electronics, memory, and optical applications. While charge carriers typically screen and suppress ferroelectricity, their role under nonequilibrium conditions remains elusive. Here, we use femtosecond laser pulses to liberate trapped carriers in ${\mathrm{LiNbO}}_3$ and track the response using time-resolved second-harmonic generation and stimulated Raman scattering. Even dilute photoexcited carriers induce a rapid yet enduring suppression of polarization and Raman susceptibility. Fluence- and temperature-dependent analyses confirm the suppression is nonthermal and arises from transient carrier screening. These findings reveal an efficient, reversible, and symmetry-preserving mechanism to modulate ferroelectricity on ultrafast timescales, offering an alternative route to control ferroic and competing quantum phases.

Single crystals of $\mathrm{Sr}{\mathrm{Mn}}_2{\mathrm{Ni}}_6{\mathrm{Te}}_3{\mathrm{O}}_{18}$, a member of the ferroaxial-type magnetic oxide family $A{B}_2{C}_6{\mathrm{Te}}_3{\mathrm{O}}_{18}$ ($A=\mathrm{Pb}$, Sr; $B=\mathrm{Mn}$, Cd; $C=\mathrm{Ni}$, Co), have been successfully grown and their structural, magnetic, magnetoelectric, and optical properties have been systematically studied. Imaging of the spatial distribution of electric-field-induced optical rotation reveals that the single crystals preferentially form single ferroaxial (FA) domains. Magnetization and neutron diffraction measurements show that $\mathrm{M}{\mathrm{n}}^{2+}$ and $\mathrm{N}{\mathrm{i}}^{2+}$ magnetic moments order antiferromagnetically at $T_{\mathrm{N}}=83$ K, forming a $c$-axis collinear bidirector-type antiferromagnetic structure. All independent magnetoelectric tensor components allowed by the magnetic point group $6/m^{\prime }$ have been detected and the ${\chi }_{33}$ component exhibits a pronounced temperature-dependent anomaly, including a peak and a sign reversal. Preferential formation of single FA domains and a similar ${\chi }_{33}$ anomaly are also observed in the isostructural compound ${\mathrm{PbMn}}_2{\mathrm{Ni}}_6{\mathrm{Te}}_3{\mathrm{O}}_{18}$. These findings suggest that the ferroaxial and magnetic characteristics within this structural framework are robust against Sr-Pb replacement.

Mercury chalcogenides are a class of materials that exhibit many structural phases under pressure, hosting exotic physical properties, including topological phases and chiral phonons. In particular, recent experimental results [Zhang et al., Phys. Rev. B 110, L060502 (2024)] on HgS report a new superconducting phase at $\sim 21\mathrm{GPa}$, whose origin is unknown. In this work, we theoretically investigate the pressure-induced structural phase transition in HgS and the resulting emergence of superconductivity. Remarkably, we find that this phase supports a two-gap superconducting state arising from distinct Fermi surface sheets. The unusually high critical temperature of $\sim 11\mathrm{K}$ emerges naturally within this multiband scenario, highlighting the role of interband coupling beyond isotropic approximation. These results place HgS among the few systems where multiband superconductivity is observed.

This work develops a method for constructing nearly flat bands with arbitrary Chern number $C$ in momentum space and further reconstructing their corresponding real-space models. In the two-band case, starting from a known topological flat band with $C=1$, we systematically generate nearly flat bands with $C=n$ through the repeated application of unitary transformations to the initial Hamiltonian. The approach is successfully applied to the Haldane model and the checkerboard model. In the three-band case, we select the simplest form of Hamiltonian and introduce unitary transformations coupled with band inversion to achieve nearly flat bands with high Chern numbers. Furthermore, for a specific type of kagome model, we separate its Hamiltonian into real and imaginary parts, and construct its coefficient vector in analogy to the two-band case, thereby also obtaining high Chern number nearly flat bands.

We develop a theory of the nonequilibrium current response for metallic systems near quantum critical points where electronic quasiparticles fractionalize, such as systems near continuous metal-insulator transitions or composite Fermi liquid to Fermi liquid transitions. Applying a generalized response theory within a Keldysh path-integral framework, we derive a nonperturbative current noise composition law, wherein the total noise is the sum of the noise of each fractionalized constituent (bosonic holons and fermionic spinons), weighted by their respective resistivities. We demonstrate that the formally derived composition relations can be interpreted in terms of a simple analogy with resistors in series. We leverage this composition rule near certain quantum critical points to show that the shot noise can be suppressed in long nanowires as compared to Fermi liquid expectations due to the collusion of quantum criticality with fractionalization.

Data analysis in angle-resolved photoemission spectroscopy (ARPES) and time-resolved ARPES usually employs derivative-based methods, such as second derivative and maximum curvature, to enhance spectral visibility. Despite their widespread use, these methods are prone to noise amplification and the introduction of artificial features. While deep learning offers a promising alternative, its effectiveness typically depends on large-scale experimental datasets. Here, we propose a Sim2Real deep learning approach that enables effective denoising without the requirement of extensive experimental data. By implementing a gradient attention U-net model, the signal-to-noise ratio is improved significantly across multiple datasets. Taking the parabolic dispersion bands for nearly free electron and the polaron features for correlated-electron phenomena as examples, our approach exhibits good performance in processing ARPES spectra, in comparison with the derivative-based methods. Moreover, our approach enables up to an $\sim 500$-fold reduction in data acquisition time—a critical advantage for time-consuming ultrafast time-/phase-resolved ARPES experiments. These capabilities underscore the potential of deep learning for quantitative, high-throughput photoemission and other spectroscopies.

Recently, a non-Hermitian Anderson impurity model with one-body loss has been studied in [K. Yamamoto et al., Phys. Rev. B 111, 125157 (2025)], and it has been demonstrated that the renormalization effect generated by strong correlations counterintuitively changes the nature of dissipation into an emergent many-body dissipation that causes a Kondo breakdown. In a closely related context, it is also known that two-body loss in a non-Hermitian Kondo model triggers the Kondo breakdown. To elucidate the essence of these phenomena, we study the Anderson impurity model with a non-Hermitian complex hybridization as an effective model that provides a simple understanding of the Kondo breakdown. Using the slave-boson mean-field theory, we show that this model can explain the Kondo breakdown with a single complex parameter. Furthermore, we provide the exact Bethe ansatz solutions that support the results obtained by the slave-boson mean-field theory.

We theoretically study photoemission spectra of photodoped one-dimensional Mott insulators that can host an excitonic bound state of a doublon and a holon known as a Mott–Hubbard exciton. We show that their spectral characteristics differ qualitatively from those of photodoped semiconductors. In conventional semiconductors, photoemission spectra are well understood; free charge carriers generate spectral weight near the bottom of the conduction band, while the formation of excitons leads to replica features of the valence band appearing inside the band gap. In one-dimensional Mott insulators, on the other hand, strong correlations give rise to fractionalized elementary excitations—spinons, holons, and doublons—which fundamentally modify the photoemission response. We find that when photodoped carriers, i.e., doublons and holons, remain unbound, the photoemission spectrum directly reflects the dispersion of spinons, i.e., magnetic elementary excitations. In contrast, when a doublon and a holon form a Mott–Hubbard exciton, replica structures of the lower Hubbard band emerge within the Mott gap, carrying contributions from both spinon and holon excitations. Importantly, the distribution of the in-gap signal depends sensitively on the degree of doublon–holon binding. The origin of these spectral features is clarified through a combination of exact diagonalization and the slave-particle approach. These results indicate that photoemission from photoinduced carriers and excitons in strongly correlated electron systems can provide information on magnetic properties and carrier binding properties.

The local electronic states of muon (Mu) as an isotope of hydrogen (H) in high-quality single-crystalline ceria (${\mathrm{CeO}}_2$) are investigated using muon spin rotation/relaxation and first-principles density functional theory (DFT) calculations. Upon positive muon implantation, both paramagnetic (${\mathrm{Mu}}^0$) and diamagnetic (${\mathrm{Mu}}^{*}$) states are observed below $\approx 10\mathrm{K}$. Magnetic field dependence of the ${\mathrm{Mu}}^0$ signals combined with DFT results provides evidence for the formation of a polaron state, consisting of Mu bonded to a ligand oxygen and a $4f$ electron localized on a nearby Ce site. The crystal-orientation dependence of the ${\mathrm{Mu}}^0$ signal suggests strong anisotropy of the $4f$ electron due to the spin-orbit coupling with lifted degeneracy. Furthermore, the ${\mathrm{Mu}}^0$ state exhibits transition to the ${\mathrm{Mu}}^{*}$ state that corresponds to another ${\mathrm{Mu}}^0$ state (exhibiting a diamagnetic response due to fast spin/charge fluctuations) at temperatures above $\approx 10\mathrm{K}$, before disappearing above $\approx 30\mathrm{K}$. These findings suggest rapid diffusive motion of the $4f$ electrons and/or Mu (as well as H) at higher temperatures.