We investigate the magnonic properties of a one-dimensional antiferromagnetic chain incorporating Dzyaloshinskii-Moriya interaction (DMI) and cross damping. By analyzing the magnetization dynamics in the linear regime, we show that the system can be mapped onto an effective modified non-Hermitian Su-Schrieffer-Heeger model. This mapping enables the application of non-Hermitian band theory, including topological invariants and the generalized Brillouin zone, to characterize the system. Within this framework, we uncover rich non-Hermitian and topological magnonic phenomena induced by the interplay of DMI and dissipative coupling. In particular, the system exhibits a bipolar non-Hermitian skin effect, where distinct magnon modes accumulate at opposite boundaries, as well as topological edge states arising from asymmetric DMI across interfaces. We further show that nonreciprocal cross damping breaks the symmetry between left- and right-localized modes and can selectively suppress edge states. Importantly, the strength of cross damping provides an effective tuning knob to control both the emergence and spatial localization of skin modes and topological edge states. Since such dissipative coupling can be engineered, for example, via spin pumping, our results establish a route toward dynamic manipulation of non-Hermitian magnonic excitations and offer a platform for designing tunable topological magnonic devices.

We establish an exact Bogoliubov sum rule for any Hermitian single-particle operator $O$: at each momentum, its particle-hole and particle-particle matrix-element weights sum to the single-particle trace ${\mathrm{Tr}}_s\left(O^2\right)$. The result follows solely from Hilbert–Schmidt-norm invariance under a canonical Bogoliubov transformation and contains neither excitation-energy denominators nor occupations; physical response identities therefore require additional assumptions. At zero field, a fully gapped helicity-diagonal state with both helicity sheets present and a spin-orbit splitting asymptotically larger than the gap obeys ${\chi }_{\mu \nu }\left(0\right)/{\chi }_N={\delta }_{\mu \nu }-{\mathrm{\Pi }}_{\mu \nu }+o\left(1\right)$, where ${\chi }_N$ is the normal-state Pauli susceptibility and $\mathrm{\Pi }={\langle {\widehat{\mathbf{n}}}_{\mathbf{k}}{\widehat{\mathbf{n}}}_{\mathbf{k}}\rangle }_{\mathrm{FS}}$ is the Fermi-surface average of the unit spin-locking texture. The eigenvalues of $\mathrm{\Pi }$ form a simplex, while the normalized spin Knight-shift tensor defines an ellipsoid whose semiaxes are the residual principal responses. Full cubic invariance of both the superconducting state and locking texture fixes $\mathrm{\Pi }=\mathbb{I}/3$ and hence $\chi \left(0\right)/{\chi }_N=2\mathbb{I}/3+o\left(1\right)$; cubic crystal symmetry alone does not. For zero-field $s$-wave pairing in the reference-Fermi-surface regime, we obtain the exact closed-form kernel $F_s\left(\lambda \right)=1-asinh\lambda /\left[\lambda \sqrt{1+{\lambda }^2}\right]$, valid for arbitrary $\lambda =\left|\mathbf{g}\right|/\mathrm{\Delta }$. In a finite Zeeman field, the zero-field helicity reduction generally fails, so the equilibrium magnetization and differential response require a self-consistent BdG calculation rather than a field-dependent locking-tensor substitution. Applied to the ${}^{75}\mathrm{As}$ data on ${\mathrm{K}}_2{\mathrm{Cr}}_3{\mathrm{As}}_3$, the framework identifies a field-dependent axial suppression pattern at 8–16 T. Both its placement near the $\widehat{c}$-axis vertex and the resulting tension with a specified decoupled-pocket spin-orbit-texture baseline require an additional fixed-tensor $T\to 0$ and zero-field extrapolation; no unique microscopic pairing state follows.

Metal intercalation and stacking engineering provide effective routes to enhance superconductivity in two-dimensional borophene-based materials. Here we focus on the $\mathit{AA}$-stacked Sr-intercalated coloring-triangle-lattice (CTL) bilayer borophene ($AA\text{−}{\mathrm{SrB}}_{18}$), identified from a systematic first-principles screening of metal-intercalated CTL bilayers. Among 20 dynamically stable metallic $M{\mathrm{B}}_{18}$ phases derived from 17 intercalated bilayers with $\mathit{AA}$ or ${AA}^{\prime }$ stacking, isotropic electron-phonon coupling calculations identify $AA\text{−}{\mathrm{SrB}}_{18}$ as the most promising superconducting candidate. We subsequently examine $AA\text{−}{\mathrm{SrB}}_{18}$ using fully anisotropic Migdal–Eliashberg calculations, which yield a $T_{\text{c}}$ of 22.2 K and reveal a weakly separated two-gap superconducting state associated predominantly with B-$\sigma$- and B-$\pi$-derived Fermi-surface sheets. The enhanced superconductivity relative to pristine CTL bilayer borophene originates mainly from Sr-induced strengthening of the electron–phonon coupling, dominated by low-frequency Sr vibrations and intermediate-frequency out-of-plane B phonon modes. In addition, $AA\text{−}{\mathrm{SrB}}_{18}$ hosts symmetry-protected Dirac crossings that are essentially unaffected by spin-orbit coupling, indicating robust topological metallic characteristics. These results establish $AA\text{−}{\mathrm{SrB}}_{18}$ as a promising two-dimensional platform exhibiting the coexistence of phonon-mediated superconductivity and nontrivial electronic topology, and highlight intercalant selection and stacking engineering as effective strategies for designing boron-rich superconducting materials.

Transition-metal (TM) substitutional defects in cubic silicon carbide (3C-SiC), which host spin-1/2 ground states with $d$-orbital character under ${\mathrm{T}}_{\mathrm{d}}$ symmetry, are emerging candidates for quantum applications. Their pseudospin parameters, including $g$ factor and effective spin-orbit splitting, are central to electron-spin resonance and quantum control. These parameters arise from the competition between spin-orbit coupling and dynamic Jahn-Teller (DJT)-mediated electron-phonon coupling. However, the microscopic mechanism governing this competition and its evolution across different TM defects remain poorly understood, severely limiting the rational engineering of these defects. Using the hybrid functional with the ${\mathrm{V}}_{\mathrm{w}}$ correction scheme (HSE + ${\mathrm{V}}_{\mathrm{w}}$), we present a systematic first-principles study of spin-1/2 $\mathrm{T}{\mathrm{M}}_{\mathrm{Si}}\left(\mathrm{TM}=\mathrm{V},\mathrm{C}{\mathrm{r}}^{+},\mathrm{M}{\mathrm{o}}^{+},{\mathrm{W}}^{+}\right)$ defects in 3C-SiC. The experimental $g_{\parallel }$ of ${\mathrm{V}}_{\mathrm{Si}}$ is reasonably captured and its deviation from the free-electron value can be attributed to covalency and DJT-mediated Ham reduction. The pseudospin parameters of group-VIB $\mathrm{T}{\mathrm{M}}_{\mathrm{Si}}$ defects are further predicted and we find that DJT-mediated electron-phonon coupling anomalously strengthens with increasing atomic number—opposite to the trend in group-IV vacancy color centers in diamond—causing the Ham reduction factor to decrease from Cr to Mo and W. This anomalous enhancement competes with the expected growth of spin-orbit coupling, substantially suppressing the growth of effective spin-orbit splitting and the $g$ factor deviation across the series. Our results establish DJT-mediated electron-phonon coupling as a key modulator of spin-orbit-driven pseudospin properties in TM defects of diamondlike materials.

We investigate localization in a one-dimensional quasiperiodic lattice obtained by extending the Aubry-André model with a structured $N\mathrm{th}$-neighbor hopping term of strength $J_N$. This additional channel connects successive windings of an effective helical chain, introducing both a hopping scale and a geometric length scale into the localization problem. Under periodic boundary conditions, we identify the localization transition using a geometric Binder cumulant $U_4$ constructed from the polarization amplitudes of the occupied many-body Slater determinant. The finite-size critical potential is extracted from the zero crossing of $U_4$. At fixed helical range $N$, increasing $J_N$ shifts the transition toward larger quasiperiodic potential strengths. In contrast, varying $N$ produces a strongly nonmonotonic phase boundary with pronounced spikelike enhancements of the critical potential. Using Fibonacci system sizes together with a Zeckendorf-shift construction for the particle number, we show that the dominant spike structure survives the thermodynamic-limit extrapolation. The largest enhancements are associated with helical ranges for which the phase shift $2\pi \beta N$ approaches an in-phase or antiphase resonance condition. We supplement the polarization analysis with occupied-state IPR and NPR, energy-resolved IPR maps, and the single-particle Fermi gap. The Fermi gap begins to open at the same crossover onset at which $U_4$ departs from its conducting-regime plateau, providing a complementary spectral signature of the same insulating transition. The participation ratios show that, in the half-filled sectors studied here, this transition is also accompanied by a gradual and energy-dependent localization of the single-particle eigenstates.

We propose a mechanism for the inverse Faraday and the inverse Cotton-Mouton effects arising from quantum geometry, characterized by the quantum metric quadrupole and the weighted quantum metric. Within a semiclassical framework based on the Boltzmann transport theory, we establish a general formalism describing light-induced magnetization in electronic systems as a second-order response to the electric field of light. Using continuum and tight-binding models, we discuss the symmetry constraints on these effects and estimate the magnitudes of the resulting magnetizations. Our results highlight a direct manifestation of quantum-geometric quantities in nonlinear magneto-optical responses and suggest possible routes toward experimental detection.

Radial vortex is a topological spin texture stabilized by the interfacial Dzyaloshinskii–Moriya interaction (DMI) in ferromagnetic disks. Previous investigations have shown that the doublet splitting of azimuthal modes in traditional circular vortices arises from the coupling between azimuthal spin waves and the vortex core (VC), an effect that occurs only for azimuthal indices $m=\pm 1$ and is absent for higher-order modes. Here, we demonstrate a giant mode splitting of azimuthal spin waves in radial vortices, even in the absence of the VC. This mode splitting arises from the DMI and can be an order of magnitude larger than that induced by the VC. Moreover, the DMI-induced frequency splitting increases with both the DMI constant and mode index, reaching tens of gigahertz for higher-order azimuthal modes. Our results reveal a robust mechanism for mode splitting in chiral magnetic textures and deepen the fundamental understanding of the DMI effect on the spin-wave dynamics in confined magnets.

As a classic high-pressure superconductor, elemental lanthanum (La) offers a vital platform for understanding tunable superconductivity. Using first-principles calculations, this study systematically investigates the strain-engineered superconducting properties and the underlying multiscale mechanisms of the ambient-pressure La-$P{6}_3/mmc$ phase. We reveal that uniaxial compressive deformation uniquely induces an anomalous enhancement in the superconducting transition temperature $\left(T_{\mathrm{c}}\right)$, which peaks at 7.5 K (a $\sim 20\%$ increase from the pristine 6.2 K) at an optimal strain of $\varepsilon =0.048$. Remarkably, this optimal superconductivity emerges despite a monotonic decrease in the global density of states at the Fermi level. We demonstrate that this paradox is resolved by a strain-driven $5s\to 5d$ interlayer charge transfer, which establishes highly localized flat-band pockets and pristine Fermi surface nesting near the $k$ point. This momentum-specific nesting sharply amplifies the electron-phonon coupling matrix elements and induces selective low-frequency acoustic phonon softening. However, excessive compression triggers a closed-to-open Lifshitz transition that destroys the nesting condition, abruptly suppressing $T_{\mathrm{c}}$. Conversely, biaxial tensile deformation monotonically reduces $T_{\mathrm{c}}$ due to a severe energetic misalignment, where localized electronic states are pushed deep below the Fermi level, rendering them ineffective for pairing. These results reveal the key interactions between orbital occupation redistribution, topological transition, Fermi surface nesting, and lattice dynamics, providing a microscopic insight into the strain-tunable superconductivity in elemental La.

We investigate the structural, electronic, and superconducting properties of a hexagonal ${\mathrm{BP}}_3$ monolayer using first-principles calculations combined with anisotropic Migdal-Eliashberg theory. The optimized structure exhibits a stable, slightly buckled configuration, as confirmed by phonon dispersion analysis and ab initio molecular dynamics simulations. The phonon spectrum indicates high-frequency vibrational modes associated with B-P bonding. Electronic band structure calculations reveal a multiband metallic state, with states near the Fermi level predominantly derived from $p_z$ orbitals of both boron and phosphorus atoms, forming two distinct Fermi surface sheets. The electron-phonon coupling is relatively strong, with a total coupling constant of $\lambda =1.59$, dominated by low- and intermediate-frequency phonon modes. Solving the anisotropic Migdal-Eliashberg equations yields a robust superconducting transition temperature ranging from $T_c=9.0$ to 9.7 K for Coulomb pseudopotentials of ${\mu }^{*}=0.13$ and 0.10, respectively. The superconducting state is characterized by a nodeless but anisotropic gap structure, exhibiting two distinct gap values (approximately 2.25 and 1.74 meV at ${\mu }^{*}=0.10$) associated with different Fermi surface sheets. These results identify the ${\mathrm{BP}}_3$ monolayer as a strongly coupled, multiband two-dimensional superconductor and provide insight into the role of orbital hybridization in electron-phonon-mediated superconductivity in low-dimensional systems.

Superconductivity with nontrivial band topology provides a platform for exploring topological superconductivity and its quantum applications. A detailed microscopic understanding of the superconducting ground state in such materials is crucial. Here, we report the results of a muon spin rotation/relaxation study $\left(\mu \mathrm{SR}\right)$ of the topologically nontrivial superconductor SnAs, which exhibits superconductivity below 3.74(1) $\mathrm{K}$. Zero-field $\mu \mathrm{SR}$ data reveal that this system is a time-reversal invariant superconductor, and systematic transverse-field $\mu \mathrm{SR}$ measurements unveil the type-I nature of the SnAs superconductor. We have established the superconducting phase diagram to understand the intermediate state of type-I superconductors. Moreover, ab initio band structure and phonon calculations are performed, which correlate with the experimental characterization.

We study quantum fluctuations in a quartet superfluid (QSF) of two-dimensional (2D) fermion mixtures with mass imbalance. Here QSF is a high-order superfluid that corresponds to the condensation of $(1+3)$ clusters, each consisting of a light fermion and three heavy ones. By incorporating the Gaussian fluctuations respecting dominant four-body correlations in this system, our theory successfully recovers the leading universal logarithmic contribution to the 2D equation of state in the deep binding regime, thereby offering a correct physical picture of quartet clusters behaving as composite bosons. By extending the Gaussian fluctuation theory from pairing to quartet superfluids, our results shed light on quantum fluctuations in general fermion superfluids with arbitrarily high-order correlations.

We develop a theoretical framework based on the nonperturbative renormalization group (RG) in the one-particle irreducible (Wetterich) formulation to tackle the interplay of coupled fermionic and order-parameter fluctuations at metallic quantum critical points (QCPs) with ordering wave vector $\vec{Q}=\vec{0}$. We consistently treat the dynamical emergence of the Landau damping of the bosonic mode and non-Fermi liquid scaling of fermions upon lowering the cutoff scale. The loop integrals of the present theory involve only contributions from fluctuations above the cutoff scale, which protects the system from developing singular bosonic interactions. We emphasize the importance of the nontrivial relative scaling of the bosonic and fermionic cutoffs $\mathrm{\Lambda }$ and ${\mathrm{\Lambda }}_f$, which we fix by analyzing the RG flow of the scale-dependent ordering wave-vector ${\vec{Q}}_{\mathrm{\Lambda }}$. Upon neglecting Fermi self-energy in the loop integrals of the functional RG flow, we identify a non-Fermi liquid RG fixed point and recover the features obtained earlier within random phase approximation-type approaches. In a subsequent step, we self-consistently include the scaling of the self-energy and the Yukawa coupling. We find a generic instability of the non-Fermi liquid RG fixed point. This implies, at least at this truncation level, absence of the QCP with $\vec{Q}=\vec{0}$ and development of a first-order phase transition or a phase characterized by $\vec{Q}\ne \vec{0}$.

Symmetry plays a central role in modern physics, from classifying quantum states to characterizing phases of matter through spontaneous symmetry breaking. In interacting fermionic systems with multiple internal degrees of freedom, however, determining the full continuous symmetry group and classifying possible order parameters remain challenging. In this work, we present a systematic framework for analyzing continuous symmetries and identifying candidate order parameters in such systems, without assuming the irreducible matter-field content or the preserved symmetry group in advance. By mapping the Hamiltonian to a Majorana representation, we obtain the generators of continuous symmetries from the Lie algebra of operators that commute with the Hamiltonian. We then identify the structure of this Lie algebra using the theory of semisimple Lie algebras. Building on representation theory, we further develop a systematic method for exhaustively enumerating candidate order parameters. By decomposing the exterior-power representations induced by the symmetry algebra on the Majorana space and incorporating discrete lattice symmetries, we classify these order parameters according to the symmetries they break. To demonstrate the power of the framework, we first apply it to the single-layer Hubbard model on a honeycomb lattice as a benchmark and recover the well-known $\mathrm{SO}\left(4\right)$ symmetry with $\mathfrak{su}\left(2\right)\oplus \mathfrak{su}\left(2\right)$ symmetry algebra. We then apply it to a bilayer spin-$1/2$ fermion model on a honeycomb lattice with Heisenberg exchange and density-density interlayer couplings, uncovering a $\mathrm{Spin}\left(5\right)\times \mathrm{U}\left(1\right)/{\mathbb{Z}}_2$ symmetry with $\mathfrak{so}\left(5\right)\oplus \mathfrak{u}\left(1\right)$ symmetry algebra. Within this setting, we systematically classify all candidate bilinear order parameters and reveal a rich landscape of potentially competing phases. The same framework has also been applied to a closely related bilayer model with pure Heisenberg interlayer coupling, which possesses an $\mathrm{SU}\left(2\right)\times \mathrm{SU}\left(2\right)\times \mathrm{SU}\left(2\right)/{\mathbb{Z}}_2$ symmetry with $\mathfrak{su}\left(2\right)\oplus \mathfrak{su}\left(2\right)\oplus \mathfrak{su}\left(2\right)$ symmetry algebra [He et al., arXiv:2603.18278].

Recent experiments on the kagome metal ${\mathrm{CsV}}_3{\mathrm{Sb}}_5$ reveal a curious phase transition-like feature: a nematic magnetic torque response that abruptly sets in at $T_{\tau }\simeq 130\mathrm{K}$, above the known charge-density wave (CDW) transition at $T_{\text{CDW}}\simeq 100\mathrm{K}$. Counterintuitively, elastoresistance measurements, a standard probe of nematicity, show no corresponding signal, ruling out a nematic phase transition and placing strong constraints on possible explanations. Beyond nematicity, the torque is paramagnetic for in-plane magnetic field, while above a critical out-of-plane field, an in-plane magnetization appears, accompanied by hysteresis. We show that this combination of features cannot be accounted for by charge-density waves or intraband magnetic order. Instead, we propose that interband ordering—via a symmetry-allowed interband spin-orbit coupling and a time-reversal and spatial symmetry-breaking interband order parameter—together with a background strain field, consistent with typical experimental conditions, provides a natural explanation; in our picture, the behavior at $T_{\tau }$ is understood as a crossover in the symmetry-allowed interband spin-orbit coupling strength. Our theory accounts for the nematic magnetic torque, hysteresis, and the transition-like onset at $T_{\tau }$, while also making testable predictions, including strain-induced magnetization. In doing so, it challenges the prevailing view of the normal state.

Ultrafast pump-probe spectroscopy was utilized to investigate coherent acoustic phonon (CAP) generation in bulk black phosphorus on ${\mathrm{SiO}}_2$ substrate, focusing on its dependence on probe wavelength, pump wavelength, and polarization. By systematically varying the pump wavelength from 400 to 800 nm, we quantitatively extracted the acoustic deformation potential (ADP) values that characterize carrier-acoustic phonon interactions in anisotropic semiconductors. The analysis reveals that both the ADP mechanism and thermoelastic stress contribute comparably to CAP generation, with their relative weights strongly dependent on excitation conditions. Pronounced anisotropy was observed when tuning the pump polarization between the armchair and zigzag (ZZ) crystallographic directions, yielding ADP values of 6.96 and 2.70 eV, respectively. Complementary density functional theory calculations and a two-valley coupling model indicate that the reduced effective ADP for pump polarization along the ZZ direction originates from intervalley carrier scattering and multivalley conduction band contributions. In this study, we establish CAP spectroscopy as a powerful, polarization-resolved probe of electron-phonon coupling and provide a general framework for quantifying deformation potentials in anisotropic, multivalley materials.

Transition metal dichalcogenide heterostructures host long-lived interlayer excitons in the $+K$ and $-K$ valleys that can encode long-lived valley polarization. We investigated the low-temperature valley polarization dynamics in an ${\mathrm{MoSe}}_2$-bilayer hBN-${\mathrm{WSe}}_2$ heterostructure. The bilayer hBN spacer results in an interlayer exciton lifetime exceeding 2 µs and an anomalous valley polarization amplification effect. Our theoretical model shows that this amplification results from the long exciton lifetime and exciton-exciton interactions. This work sets the stage for long-lived interlayer excitons to be used in nonlinear valleytronic transistors and amplifiers.

We show a high-purity crossed Andreev reflection (CAR) in a fully nonmagnetic junction, which features a superconductor layer sandwiched between two leads with gate-tunable opposing Rashba fields. A scattering matrix method is developed to quantify the high-purity CAR by calculating the full scattering processes comprising reflection and transmission. The underlying mechanism, which we term chiral Rashba matching, leverages the mutually exclusive opposite spin textures in the two leads to suppress nonlocal electron cotunneling (CT) while enhancing CAR. Remarkably, we show that the high-purity CAR can be switched on/off as desired via tuning either the Fermi level or the driving bias. Our proposed all-electrical, magnetic-element-free scheme for CAR enables simpler and more scalable architectures for on-chip quantum entanglement generation.

Valley coherence is of great significance for exploring fundamental quantum phenomena and developing next-generation valleytronic devices. Herein, we theoretically investigate the valley quantum interference engineered by inter-Landau level (LL) transitions in black phosphorus (BP) and ${\mathrm{WTe}}_2$ monolayers. In contrast to the non-Landau-quantized regime, valley quantum interference is enhanced by over 20-fold, or even significantly stronger, in virtue of the striking anisotropic environment. Such anisotropy originates from the distinct electron transition probabilities along the armchair and zigzag directions of BP and ${\mathrm{WTe}}_2$ monolayers. Specifically, BP is capable of more effectively strengthening the valley quantum interference response due to its greater directional disparity in electron transition probabilities. The interference fringes also present distinct spectral profiles (e.g., different dip and peak numbers in one interference period) owing to different transition selection rules in BP and ${\mathrm{WTe}}_2$ monolayers. In spite of these discrepancies, normalized interference intensities can be phenomenologically fitted by two exponential functions of magnetic field and LL index for all the transitions $\delta n=n^{\prime }-n=0$, ±2, ±4 (where $n$ and $n^{\prime }$ indicate the LL indexes of the valence and conduction bands, respectively), and the interference spectra exhibit ${\mathrm{C}}_2$ rotational symmetry about the crystallographic azimuthal angle of 90°.