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°.

In modern nanostructures with very low defect densities, a hydrodynamic regime of electric transport has recently been realized in which two-dimensional (2D) electrons form a viscous fluid due to frequent electron-electron collisions. Many bright transport phenomena have been observed in these systems. Of particular interest are two-component hydrodynamic electron systems where a richer variety of phenomena becomes possible than in one-component systems. The simplest way to implement and control a two-component 2D electron system is to place a structure with 2D electrons in a magnetic field with a large component in the 2D plane, which leads to a Zeeman splitting of the electron energy spectrum into two subbands. Here we develop a microscopic model of hydrodynamic transport in such systems. By solving the kinetic equation, we calculate the electron-electron relaxation rates of the first and second angular harmonics of the two-component distribution function. Then we derive the hydrodynamic balance equations with the kinetic coefficient containing these rates. Namely, we take into account the shear viscosity in each fluid component and the effect of the friction between the two components. The latter leads to equalization of the hydrodynamic velocities in the two subbands. The obtained equations can be used to explain the results of puzzling magnetotransport experiments in ultrapure nanostructures in a strong oblique magnetic field.

We study the low-energy effective theory of spin-1/2 quantum ice on the planar pyrochlore lattice from the perspective of its global symmetries. We show that the Fourier transform of the spin operator $S_{\mathbf{Q}}^z$ can be expressed in terms of conserved quantities associated with a one-form U(1) symmetry along two high-symmetry momentum paths, leading to constraints on both the static and dynamical structure factors. We also derive Lieb–Schultz–Mattis type constraints that forbid the existence of a unique gapped ground state in the low-energy effective theory. Our findings also apply to the $(2+1)$-dimensional U(1) quantum link model.

We investigate the emergence of altermagnetic (AM) phases on the square-kagome lattice. Our analysis reveals that matrix element effects due to an orthogonal sublattice weight decomposition of Fermi level eigenstates known as sublattice interference enable decoupled magnetic ordering tendencies on distinct sublattices. Depending on which sublattice undergoes a magnetic instability, we identify a $d_{xy}$-type AM phase and a $d_{x^2-y^2}$-type AM phase originating from different sublattice polarization patterns. Using the Kotliar-Ruckenstein slave boson formalism, we explore the stability of these AM phases as a function of interaction strength. Our findings demonstrate that sublattice-selective magnetic instabilities provide a versatile route to engineer the nature of AM order.

Topological kink states are inherently tied to valley-based topological charges, and extending this framework is critical for enhancing quantum transport efficiency. Using tight-binding models, we demonstrate that even-spin-Chern (ESC) insulators offer a versatile platform for realizing new classes of topological kink states when integrated with quantum spin/valley Hall (QSH/QVH) insulators. A buckled ESC/QVH junction hosts topological multifold kink (TMK) states arising from multiple topological charge sources, yielding highly spin-polarized, dissipationless chiral channels. A planar ESC/QSH junction supports a mirror-protected topological crystalline kink (TCK) state with six channels that markedly enhance the transport efficiency. Interfacial hopping governs the emergence of gapless topological kink states. Density functional theory calculations identify the Pb/${\mathrm{SbAsH}}_2$ junction as an exemplary candidate for realizing disparate TMK states. Our work establishes ESC insulators as a promising foundation for high-performance quantum topological devices and provides insights into the classification and microscopic origins of topological kink states.

Three-dimensional (3D) quantum Hall effect (QHE) of Fermi arcs in Weyl semimetals has attracted significant interest. In this work, we explore the 3D QHE of Fermi arc surface states in tilted Weyl semimetals. We systematically consider both the symmetric the and asymmetric tilts. For the asymmetric tilt, the Fermi arcs form a straight line, which cannot support the 3D QHE irrespective of the value of the tilt. However, for the symmetric tilt, when the tilt increases from zero to finite values in type I, the intersection geometry of Fermi arcs undergoes a transformation from null crossing to finite-area overlap, which corresponds to a nonzero Hall conductivity. Meanwhile, the Landau levels exhibit asymmetric energy distribution with respect to the Fermi level at Weyl nodes, which prevent the cancellation between contributions from electronic states above and below the Weyl nodes, leading to the nonvanishing Hall conductivity. This topological reconstruction suggests that the nonzero symmetric tilt can modulate the 3D QHE in Weyl semimetals. We also demonstrate that the intersection area between Fermi arcs increases with the symmetric tilt strength, while the Hall plateau width decreases. The sheet Hall conductivity follows the conventional $1/B$ dependence, while its slope shows tilt-enhanced behavior. Our study provides critical insights into the interplay between the tilt and the 3D QHE of Fermi arc surface states in tilted Weyl semimetals.