The pursuit of high-temperature quantum anomalous Hall (QAH) insulators faces fundamental challenges, including narrow topological gaps and low Curie temperatures ($T_{\text{C}}$) in existing materials. Here, we propose a transformative strategy using bilateral hydrogenation to engineer a robust QAH state in the topologically trivial ferromagnetic semiconductor ${\mathrm{Cr}}_{\text{2}}{\mathrm{Ge}}_{\text{2}}{\mathrm{Te}}_{\text{6}}$ via covalent orbital reconstruction. First-principles calculations reveal that by fundamentally rewiring the underlying orbital hybridization network, hydrogenation alters orbital occupations to shift preexisting Dirac points—originally embedded in the conduction bands—to the vicinity of the Fermi level in ${\mathrm{Cr}}_{\text{2}}{\mathrm{Ge}}_{\text{2}}{\mathrm{Te}}_{\text{6}}{\mathrm{H}}_{\text{6}}$. This electronic restructuring, coupled with spin-orbit coupling, opens a global topological gap of 118.1 meV, establishing a robust QAH state with Chern number $C=$ 3. Concurrently, this same orbital reconstruction effectively tunes the energy difference between the ligand $p$ and transition metal $d$ orbitals. This specific energy shift enhances ferromagnetic superexchange via the $d_{z^2}\text{−}{p}_z\text{−}{d}_{xz}$ channel, significantly strengthening the nearest-neighbor coupling $J_{\text{1}}$ by 3.06 times and switching $J_{\text{2}}$ from antiferromagnetic to ferromagnetic. Monte Carlo simulations based on the extracted exchange parameters indicate a pronounced enhancement of ferromagnetic stability compared with pristine ${\mathrm{Cr}}_{\text{2}}{\mathrm{Ge}}_{\text{2}}{\mathrm{Te}}_{\text{6}}$, and we stress that the absolute Curie temperature depends on the mapping to an effective spin model and thus should be interpreted primarily in terms of relative trends. The comparative enhancement of ferromagnetic stability after hydrogenation is a salient effect of this orbital tuning. This work establishes targeted orbital reconstruction driven by surface hydrogenation as a powerful route to simultaneously control topology and magnetism in 2D materials, providing a general route to engineer QAH phases with large gaps and high Chern numbers in van der Waals ferromagnetic semiconductors.

In this work, we report coherent perfect absorption (CPA) of anti-modes in an indirectly coupled magnon–polariton system. By examining both single and indirectly coupled cases, we experimentally distinguish the modal decay rate $\gamma$ from the effective decay rate ${\gamma }_{\mathrm{eff}}$. At CPA, ${\gamma }_{\mathrm{eff}}=0$, leading to a vanishing output and a visually narrow spectrum in the dB scale, while the intrinsic linewidth set by $2\gamma$ remains unchanged, demonstrating that the effective decay rate dictates the spectral amplitude rather than the physical loss. Furthermore, in the indirectly coupled system, CPA persists over a broad, magnetically tunable detuning range, in contrast to the single-detuning CPA observed in the directly coupled case, thereby enabling magnetically reconfigurable and frequency-selective microwave absorbers.

We incorporate spin-orbit coupling (SOC) into effective Kugel-Khomskii models for the $n=1$ and $n=2$ members of the Ruddlesden-Popper series ${\mathrm{Sr}}_{n+1}{\mathrm{Cr}}_n{\mathrm{O}}_{3n+1}$. These models contain interacting spins 1 and pseudospins 1/2 at each site describing spin and orbital degrees of freedom, respectively. We solve the models at zero temperature using pseudospin bond operators and spin waves. We find that for realistic parameters, SOC dominates the physics of the compound ${\mathrm{Sr}}_2{\mathrm{CrO}}_4$ with almost decoupled single ${\mathrm{CrO}}_2$ planes. The spin ordering is antiferromagnetic, with nearest-neighbor Cr spins aligned antiparallel. The corresponding orbital configuration is $d_{xy\uparrow }^1(d_{xz\uparrow }^1-i{d}_{yz\uparrow }^1)$ or $d_{xy\downarrow }^1(d_{xz\downarrow }^1+i{d}_{yz\downarrow }^1)$ depending on the spin of the site. In contrast, for the bilayer compound ${\mathrm{Sr}}_3{\mathrm{Cr}}_2{\mathrm{O}}_7$ we find that the effect of the SOC is weak and the system prefers to form pseudospin singlets in the $z$ direction perpendicular to the planes. The spin order is antiferromagnetic within each plane and ferromagnetic between planes, in agreement with previous studies.

We develop a general theory of crystal truncation rod (CTR) scattering from vicinal surfaces with a coherently strained heteroepitaxial film. The formalism incorporates film-induced interference fringes, full elastic lattice distortion, terrace ordering, surface reconstruction, and real-time growth evolution within a unified description. Comparison between the Nagai model and the elasticity-based model shows that the lattice tilt is nearly identical in the two approaches, whereas the elasticity-based model predicts an additional triclinic deformation arising from shear strain. This deformation has little effect on specular CTRs but strongly modifies nonspecular rods, making them a sensitive probe of the full elastic state of coherent epitaxial films. We further show that the characteristic sensitivity of vicinal CTRs to terrace ordering, surface reconstruction, and terrace-resolved compositional modification remains robust in the presence of a coherent film. Representative calculations for InGaN/GaN demonstrate that the framework enables quantitative interpretation of both static and real-time CTR measurements and provides access to step- and terrace-resolved structural and kinetic information during heteroepitaxial growth.

We describe a case of instability of the paramagnetic order in an electron gas confined in a thin tubular semiconductor nanowire with a Rashba spin-orbit interaction. This situation is realized when, for a critical value of the Rashba coupling constant ${\alpha }_c$, dependent only on the radius of the tube, single-particle energies corresponding to opposite spin orientations along the direction tangent to the tube become equal. A theory of the magnetic phase transition considers the presence of the Coulomb interaction, evaluated within the Hartree-Fock approximation, which lifts the spin degeneracy and leads to the formation of quasiparticle states that support a continuous rotation of the electron spin in the momentum space along the axis of the wire. For a chemical potential localized within the gap between the quasiparticle states, the long-range magnetic order manifests macroscopically through a constant radial spin polarization proportional with the magnitude of the gap.

In a magnetic field, bilayer graphene hosts an octet of pseudo-zero-mode (PZM) electron levels nearly degenerate in orbitals $n=(0,1)$, valleys, and spins. They split in valleys by electrostatic gating. In gated bilayer graphene, in which the interlayer bias is set up to flip sign across a line, one has a line junction that traps a portion of PZM electrons inside the insulating bulk band gap, giving rise to electron states localized along the junction, known as kink states. A close look is made into the spectra and electromagnetic response of such kink states. There are two species of valley current associated with them, a drift current driven by the bias gradient and a circulating current coming from cyclotron motion. It turns out that they both flow in essentially the same direction, with the circulating current exhibiting a magnetic character distinct from those of other higher levels. In equilibrium, they spatially circulate within the kink states, creating a quasi-one-dimensional channel of orbital magnetization. The electric control of the orbital magnetization and valley currents via a network of gated junctions will find useful applications in valley electronics.

We study the ground-state phase diagram of the spin-$1/2$ Kitaev-Heisenberg model on the bilayer honeycomb lattice with large-scale tensor-network calculations based on the infinite projected entangled pair state (iPEPS) technique with the simple-update scheme, as well as high-order series expansions using perturbative continuous unitary transformations (pCUTs). We find that beyond various magnetically ordered phases, including ferromagnetic, zigzag, antiferromagnetic (AFM), and stripy states, two extended quantum spin liquid phases arise in proximity of the Kitaev limit. While these phases also appear in the monolayer Kitaev-Heisenberg model, our results further show that a valence bond solid (VBS) phase emerges in a relatively narrow range of parameter space between the AFM and stripy states. This VBS state can be adiabatically connected to isolated Heisenberg dimers. Our results highlight the importance of interlayer interactions on the emergence of quantum phases in the bilayer Kitaev materials.

We investigate the quantum phase diagram of an “odd” variant of the two-dimensional Ising Fradkin-Shenker model, characterized by a uniform background of static $e$ and $m$ charges. Using large-scale tensor network and exact diagonalization methods, we determine the topology of the phase diagram, identifying an “odd” deconfined phase, confinement- and Higgs-induced valence bond solids (VBS), and a trivial paramagnet. Most notably, we uncover an exotic multicritical point along the self-dual line, where electric and magnetic excitations are related by an enriched ${\mathbb{Z}}_2$ duality. This transition is marked by the simultaneous onset of confinement, Higgs condensation, translational symmetry breaking, and spontaneous duality symmetry breaking. Within our numerical accuracy, the transition appears continuous, involving the softening of excitation gaps for $e$ and $m$ anyons at finite momentum. At intermediate couplings, we further identify VBS phases with enlarged unit cells, potentially indicating frustration-induced crystalline order beyond commensurate limits.

Three-dimensional topological semimetals like type-II Weyl semimetal transition metal dichalcogenides $(T_d{\text{-WTe}}_2 \text{and} {\mathrm{MoTe}}_2)$ exhibit intriguing phenomena associated with various symmetries governing their band structure. Density functional theory-based band structure calculations and angle-resolved photoemission spectroscopy studies on $T_d{\text{-WTe}}_2$ have showcased the temperature-dependent variation of chemical potential and Fermi surface modifications. In this work, the decisive role of the complex band dispersion and Fermi surface topology changes (FSTCs) of ${\mathrm{WTe}}_2$ in modulating the scattering channels for charge carriers has been studied using low-frequency resistance noise spectroscopy, a transport-based probe extremely sensitive to disorder dynamics and charge carrier interference. A nonmonotonic dependence of noise with temperature is observed, with noise peaks close to temperatures associated with FSTCs in $T_d{\text{-WTe}}_2$ due to disappearance of specific carrier pockets in the Fermi surface. The time reversal symmetry in the spin-textured band structure of ${\mathrm{WTe}}_2$ is broken in a finite magnetic field leading to the emergence of additional scattering channels for the charge carriers that influence the resistance noise and the scattering timescales.

We investigate the evolution of conductance quantization and subband structure in a weakly confined quasi-one-dimensional channel as a function of carrier density and perpendicular magnetic field. As the carrier density is reduced, the $2e^2/h$ plateau is progressively suppressed and an avoided crossing develops between the lowest two subbands in transconductance, indicating a strong intersubband coupling. This behavior is consistent with an interaction-driven restructuring of the electron system into a zigzag or two-row configuration in the regime of dominant Coulomb interactions. The application of a perpendicular magnetic field suppresses the anticrossing through enhanced magnetoelectric confinement, which reduces inter-row tunneling and hybridization via magnetic compression of the wave function. At intermediate fields ($\sim 0.5\mathrm{T}$), further reduction of carrier density leads to the emergence of the $0.7(2e^2/h)$ feature coexisting with the restored $2e^2/h$ plateau. In addition, spin-split features, such as $1.5(2e^2/h)$, begin to resolve in higher subbands in the low-density, weakly confined regime. At higher fields ($\sim 0.7\mathrm{T}$), where the anticrossing is fully quenched, the low-density regime exhibits the coexistence of conductance features near $2e^2/h, 0.7(2e^2/h)$, and $0.5(2e^2/h)$. These observations indicate that perpendicular magnetic fields predominantly modify the orbital spectrum while leaving the strongly correlated spin sector intact. The resulting transport reflects the interplay between Coulomb interactions, exchange coupling, and Zeeman splitting, placing the system near the crossover between spin-coherent and spin-incoherent regimes.

The lead transition metal oxides ${\mathrm{PbTiO}}_3, {\mathrm{PbZrO}}_3$, and ${\mathrm{PbHfO}}_3$ are shown to be extremely similar in their overall properties, such as soft-mode behavior, phase transitions, and long-wavelength related characteristics. However, locally, they develop very different qualities because, as the ${\mathrm{BO}}_6$ mass increases (where B ≡ Ti, Zr, Hf), the anharmonicity of each compound increases significantly, leading to the formation of intrinsically localized modes (ILMS) or discrete breathers (DBS). This explains their exceptionally flat transverse acoustic modes. These nonlinear excitations are observed in birefringence measurements, where their coexistence with the phonon spectrum is demonstrated. While the soft modes, whether normalized by mass or temperature (long-wavelength optic and zone boundary acoustic modes), follow nearly identical temperature dependencies, the transverse acoustic modes exhibit a highly dispersion-free momentum dependence, characteristic of ILMS or DBS. Crucially, our findings support the earlier notion that the unusual dynamics are solely due to the ${\mathrm{BO}}_6$ polarizable unit, with the Pb subarrays acting merely as spectators. Furthermore, these results provide a unique explanation for the appearance of the transient phase below the phase transitions of ${\mathrm{PbZrO}}_3$ and ${\mathrm{PbHfO}}_3$, which appears to be intrinsic to these two compounds.

Synchrotron X-ray diffraction measurements of holmium were conducted up to 327 GPa using toroidal diamond-anvil cells, revealing a complete structural sequence of $\mathrm{hcp}\to \text{Sm-type}\to \mathrm{dhcp}\to \mathrm{dfcc}\to oF16\to oF8$. The $oF16\to oF8$ transition initiates around 257 GPa, approximately 60 GPa higher than that in dysprosium, and these two phases coexist up to the highest pressure studied. The transition proceeds sluggishly without a measurable volume discontinuity, indicating an anisotropic lattice rearrangement rather than abrupt $4f$ electron delocalization. The $oF8$ phase exhibits the highest incompressibility among the observed phases, completing the systematic evolution of the heavy lanthanides and underscoring the unified $oF16\to oF8$ sequence in $4f$ and $5f$ metals. First-principles calculations of phonon dispersion and enthalpy indicate that both $oF16$ and $oF8$ are dynamically stable at 325 GPa and remain nearly degenerate over a broad pressure range, consistent with the experimentally observed phase coexistence. Based on comparative analysis, this work also discusses potential method optimizations for high-pressure structural studies of rare-earth metals using toroidal diamond-anvil cells, including calibrant and gasket configurations that could improve data quality in future multi-megabar investigations.

Understanding how ${\mathrm{ABO}}_4$ oxysalt frameworks respond to compression is essential for constraining the lattice-dynamical mechanisms that govern pressure-induced structural transitions. However, intrinsic lattice instabilities are often obscured during static compression by broad mixed-phase regions. Here we measured longitudinal sound velocities ($V_{\mathrm{P}}$) of barite (${\mathrm{BaSO}}_4$) and celestite (${\mathrm{SrSO}}_4$) under shock compression up to ∼10 GPa, and performed first-principles stress-strain calculations for ${\mathrm{BaSO}}_4$. Our results show that the $V_{\mathrm{P}}$ of celestite varies smoothly with pressure over the investigated range, whereas barite exhibits a ∼6% decrease in $V_{\mathrm{P}}$ between ∼5.2 and ∼7.0 GPa. This anomaly is consistent with the $Pnma\to P{2}_1{2}_1{2}_1$ phase transition in ${\mathrm{BaSO}}_4$ but occurs at substantially lower pressure and within a narrower pressure interval than under static compression. First-principles calculations show that the Pnma lattice becomes unstable at shear stresses of ∼1.7–3.5 GPa, close to the estimated shock-induced deviatoric stresses, and that the instability involves cooperative tilting of ${\mathrm{SO}}_4$ tetrahedra and distortion of Ba–O polyhedra. These results suggest that high strain-rate shock loading couples transient deviatoric stresses to lattice instabilities, enabling access to the transition prior to equilibrium relaxation. The observed $V_{\mathrm{P}}$ softening provides experimental support for an underlying lattice instability associated with the transition. Our results highlight that sound-velocity measurements under shock compression can provide a sensitive probe of incipient lattice instability in ${\mathrm{ABO}}_4$ frameworks and illustrate how strain-rate-assisted shear instabilities reshape phase-transition pathways in complex oxysalts.

Spectroscopy serves as a key experimental pathway for probing many-body dynamics. Among them, high-harmonic generation (HHG) spectroscopy is particularly valued for its subcycle temporal resolution. Recent investigations have confirmed that excitonic effects in crystals can significantly enhance harmonic signal yield. The influence of excitonic effects on harmonic frequency have yet to be addressed. In this work, we theoretically demonstrate the collaboration mechanism to the frequency shift in the high-harmonic spectrum through two key excitonic effects: band gap renormalization and Rabi frequency renormalization. The observed band gap renormalization leads to an asymmetry of harmonic emission efficiency between the rising and falling edges of the driving laser pulse, with higher efficiency during the falling edge. This further results in a redshift of the harmonic spectrum. By contrast, the Rabi frequency renormalization with Pauli-blocking correction exhibits a tendency toward a blueshift via enhanced rising-edge emission, yet its synergy with band gap renormalization results in a pronounced redshift. In this work, we establish a direct link between exciton dynamics and the HHG process.

Classical nonlinear theories are highly successful in describing far-from-equilibrium dynamics in magnetism, including phenomena such as parametric resonance, ultrafast switching, and even chaos. However, at ultrashort length and time scales, where quantum correlations become significant, these models inevitably break down. While numerous methods exist to simulate quantum many-body spin systems, they are often limited to near-equilibrium conditions, capture only short-time dynamics, or obscure the intuitive connection between nonlinear behavior and its geometric origin in the $\mathfrak{su}\left(2\right)$ spin algebra. To advance nonlinear magnetism into the quantum regime, we develop a theory in which semiclassical spin correlations, rather than individual spins, serve as the fundamental dynamical variables. Defined on the bonds of a bipartite lattice, these correlations are inherently nonlocal, with dynamics following through a semiclassical mapping that preserves the original spin algebra. The resulting semiclassical theory captures nonlinear dynamics that are fundamentally nonclassical and naturally incorporates phenomenological damping at the level of correlations, requiring significantly less effort than quantum many-body approaches. As an application, we focus on Heisenberg antiferromagnets, which feature significant quantum effects. We predict nonlinear scaling of the mean frequency of quantum oscillations in the Néel state exhibit a nonlinear scaling state with the spin quantum number $S$. These oscillations have no classical analog and exhibit features reminiscent of nonlinear parametric resonance, as fully confirmed by exact diagonalization. The predicted dynamical features are embedded in the geometric structure of the semiclassical phase space of spin correlations, making their physical origin much more transparent than in full quantum methods. With this, semiclassical spin-correlation dynamics provide a foundation for exploring nonlinear quantum magnetism.

We investigate the chromium breathing-pyrochlore sulfide ${\mathrm{AgInCr}}_4{\mathrm{S}}_8$, a chromium-based thiospinel, by synchrotron x-ray and neutron powder diffraction, dc magnetization, and heat capacity. Diffraction confirms the $F\overline{4}3m$ breathing structure with alternating large and small $\mathrm{C}{\mathrm{r}}_4$ tetrahedra, a large breathing ratio ($d^{\prime }/d=1.106$ at 300 K), and substantial Ag/In intermixing on the $A$ sublattice ($\sim 16\%$). No structural transition or magnetic Bragg peaks are detected down to 1.5 K. An enlarged low-angle difference plot between the 1.5 and 20 K neutron diffraction patterns shows a weak broad diffuselike enhancement, consistent with short-range or frozen correlated moments within the sensitivity of the present data. Susceptibility yields a positive Weiss temperature ${\theta }_{\mathrm{W}}=+92\mathrm{K}$ and a moment enhancement in 30–60 K, while the magnetic entropy released by $\sim 30\mathrm{K}$ approaches a scale of order $R$ ln 13, together consistent with the development of short-range tetrahedral ferromagnetic correlations and an effective $S=6$ cluster-moment picture. A broad susceptibility cusp with ZFC–FC bifurcation and a low-temperature specific-heat anomaly near 9 K indicate a phenomenological glassy-freezing anomaly without long-range order. ${\mathrm{AgInCr}}_4{\mathrm{S}}_8$ provides a benchmark for the interplay of strong breathing distortion and quenched $A$-site disorder in chromium breathing pyrochlores.

Unconventional antiferromagnets with intrinsic spin splitting enable spin-polarized transport similar to ferromagnets with zero net magnetization, offering substantial potential applications in high-density, nonvolatile spintronic devices. However, achieving efficient electric-field controlled tunneling magnetoresistance (TMR) still remains a fundamental challenge. Here, we propose a general strategy based on symmetry design—constructing mirror-time reversal (${\widehat{M}}_z\widehat{T}$) symmetry—to effectively regulate antiferromagnetic TMR. Using bilayer $\mathrm{Mn}{\mathrm{Sb}}_2{\mathrm{Se}}_4$ as a model system, we demonstrate that van der Waals stacking breaks combined inversion and time reversal symmetry ($\widehat{P}\widehat{T}$), driving a transition from a spin-degenerate state to a spin-splitting unconventional antiferromagnetic phase with zero net magnetic moment. This system hosts two stable states with opposite interlayer electric polarizations, linked by ${\widehat{M}}_z\widehat{T}$ symmetry, which allows an external electric field to reversibly switch the spin-texture alignment. Accordingly, we construct an antiferromagnetic tunnel junction that achieves reversible resistance switching via polarization reversal without altering magnetic order, yielding a nonvolatile TMR ratio up to 300%. All these findings establish feasible pathways towards low-power, high-density antiferromagnetic spintronic devices.

We study the Josephson effects in the spin-triplet superconductor/altermagnet/spin-triplet superconductor junctions using the Green's function method. It is found that the current-phase difference relationships in the junctions strongly depend on the direction of the $\mathbf{d}$-vectors in the spin-triplet superconductors and the orientation angle of the altermagnet. For the given orientation angle, the 0-$\pi$ transition can be obtained when the $\mathbf{d}$-vector is rotated. The variations of the critical current of the junctions with the direction of the $\mathbf{d}$-vector, the orientation angle and the strength of altermagnetism are systematically investigated. These Josephson effects can provide the distinguishable information about the direction of the $\mathbf{d}$-vector. Compared to the existing research, the proposed altermagnetic Josephson junctions can effectively avoid the negative influence of the magnetic field on the $\mathbf{d}$-vector and can serve as a feasible scheme for the detection of the intrinsic $\mathbf{d}$-vector. The obtained 0-$\pi$ transition in the junctions can also have potential applications in the design of quantum devices.