Homogeneous in-plane biaxial tensile strain strengthens the out-of-plane van der Waals (vdW) interaction in ${\mathrm{MoS}}_2$ bilayers (BLs) and can be used to fine tune their terahertz (THz) oscillations. Using ultralow-frequency Raman spectroscopy on hexagonal (2H) and rhombohedral (2R) stacked BLs, we observe a hardening of the interlayer breathing modes originating from a strain-induced Poisson contraction of the vdW separation between the layers characterized by an effective out-of-plane Poisson's ratio of ${\nu }_{\mathrm{eff}}\approx 0.19\text{–}0.24$. Strikingly, this geometric contraction drives the system into a highly repulsive regime of the intermolecular potential, corresponding to a Grüneisen parameter of $\gamma \approx 14\text{–}20$. This value surpasses even the “giant” one reported for phosphorene, establishing these vdW BLs as highly tunable nonlinear mechanical platforms that can be addressed at the THz regime without external pressure knobs.

Several unconventional superconducting phases have been discovered close to a metamagnetic transition in the heavy-fermion compound ${\mathrm{UTe}}_2$. Although suspected to be of magnetic nature, the mechanisms stabilizing these superconducting phases remain mysterious. Here, we present electrical-resistivity measurements on ${\mathrm{UTe}}_2$, with a current $\mathbf{I}\parallel \mathbf{a}$ and under pulsed magnetic fields up to 60 T rotating in the $(\mathbf{b},\mathbf{c})$ plane. We find that the maximum of the Fermi-liquid coefficient $A$ at the metamagnetic transition is enhanced under magnetic fields tilted by ${30}^{\circ }\text{–}{40}^{\circ }$ from $\mathbf{b}$ to $\mathbf{c}$. The enhancement of $A$ coincides with the stabilization of superconductivity in the polarized paramagnetic regime beyond the metamagnetic field ${\mu }_0{H}_m\gtrsim 40\mathrm{T}$. It is the signature of a boosted quantum-critical magnetic-fluctuation mode probably in play for the mechanism of this superconducting phase. This result appeals for descriptions of the interplay between magnetic-field-induced superconductivity and quantum-critical magnetic properties.

Understanding how strong electronic correlations shape superconductivity remains a central challenge in quantum materials. In multiorbital systems, correlations driven by Hund's coupling can differentiate the behavior of individual orbitals, producing the so-called Hund's metal state. How such orbital-selectivity also governs superconducting pairing, however, has remained largely unexplored experimentally. Here we use high-resolution angle-resolved photoemission spectroscopy to systematically map the superconducting gap structure across the phase diagram of the representative iron-based superconductor ${\mathrm{Ba}}_{1-x}{\mathrm{K}}_x{\mathrm{Fe}}_2{\mathrm{As}}_2$. We find that superconductivity evolves in a strongly orbital-dependent manner: the gap associated with the $d_{xy}$ orbital collapses beyond optimal doping while pairing on the $d_{xz}/d_{yz}$ orbitals persists. This behavior mirrors the orbital-selective correlations observed in the normal state and reveals a direct connection between Hund's metal physics and the superconducting pairing landscape. Our results demonstrate that superconducting gaps themselves can serve as a sensitive probe of orbital-dependent correlations and suggest that Hund's coupling plays a central role in shaping pairing in multiorbital superconductors.

Spin-orbital liquids provide an exactly solvable route to three-dimensional ${\mathbb{Z}}_2$ quantum spin liquids beyond the original Kitaev setting. Built from higher-dimensional Clifford-algebra representations, spin-orbital Hamiltonians can be realized on both three- and four-coordinated lattices, giving rise to phases with $\nu =3$ and 2 itinerant Majorana flavors, respectively. We demonstrate that these models host a rich set of gapless Majorana metals, characterized, in particular, by topological Fermi surfaces, nodal lines, and Weyl semimetal phases. We analyze the stability of these structures under physically motivated perturbations and identify generic splitting patterns and topological transitions driven by symmetry breaking and flavor mixing. This yields a unified organizing framework for three-dimensional Majorana metals in fractionalized spin liquids.

Quantum mechanical lattice models with local, bounded interactions obey Lieb-Robinson causality. We show that this implies a domain of analyticity of the retarded Green's function $G^R(\omega ,\mathbf{k})$ of local lattice operators as a function of complex frequency $\omega$ and momentum $\mathbf{k}$, similar to the light-cone analyticity property of relativistic field theories. Low-energy effective descriptions of the dynamics must be consistent with this microscopic analyticity constraint. We consider two canonical low-energy fermionic Green's functions describing non-Fermi liquids, the marginal Fermi liquid and the ‘‘Hertz liquid.’’ The pole in these Green's functions must be outside of the Lieb-Robinson domain of analyticity for all complex momenta captured by the low-energy theory. This constraint upper bounds the magnitude of the dimensionless non-Fermi-liquid coupling in certain Hertz liquids.

We investigate the phase diagram of moiré double bilayer transition metal dichalcogenides with ABBA stacking as a function of twist angle and applied pressure. At hole filling $\nu =2$ per moiré unit cell, the noninteracting system hosts a Dirac semimetal with graphenelike low-energy bands in the moiré Brillouin zone. At small twist angles, the Fermi velocity is reduced, and interactions dominate the low-temperature behavior. A strong-coupling analysis identifies insulating ferromagnetic and antiferromagnetic ground-state candidates, characterized by spin-density modulations set by the moiré scale. Using a realistic continuum model with long-range Coulomb interactions, we perform self-consistent Hartree-Fock calculations to study the competition between these states. Varying the twist angle or pressure drives a transition from a Dirac semimetal to an antiferromagnetic insulator, which breaks SU(2) spin rotation and twofold lattice rotation symmetries. Within a renormalization group analysis of the most general symmetry-allowed low-energy field theory, we show that this semimetal-to-insulator transition is continuous and belongs to the $(2+1)\mathrm{D}$ relativistic Gross-Neveu-Heisenberg universality class with $N=2$ four-component Dirac fermions. Finite heterostrain, relevant in realistic samples, induces a crossover from Gross-Neveu-Heisenberg universality at intermediate temperatures to conventional $(2+1)\mathrm{D}$ Heisenberg criticality at the lowest temperatures. Further decreasing the twist angle can cause a level crossing from the antiferromagnetic insulator into a ferromagnetic insulator with spin-split bands. Our results provide a comprehensive theoretical framework that complements and elucidates recent experiments in twisted double bilayer ${\mathrm{WSe}}_2$.

The edge spin galvanic effect (ESGE) in $d$-wave altermagnets is proposed. ESGE is a creation of an electrical current flowing along the edge of the sample, which is driven by the spin orientation of charge carriers. The ESGE current is formed owing to the altermagnetic spin splitting and the scattering of carriers by the edge of the sample. The current is sensitive to the orientation of the edge in respect to the main axes of the altermagnet. The edge spin galvanic current reverses its direction upon a reversal of the nonequilibrium spin direction or the Néel vector. We show that the effect is a universal consequence of $d$-wave spin splitting and vanishes for purely isotropic spin splitting. We also propose the pure spin edge photocurrent excited by polarized radiation and formed at the edges of a sample. Its dependence on the radiation polarization and frequency is analyzed. The application of an external magnetic field converts this pure spin photocurrent into an electric current along the edge.

Atomically thin moiré materials behave like elastic membranes in which, at very small twist angles, the van der Waals stacking energy much exceeds the elastic energy. In this “marginal twist” regime, the equilibrium moiré consists of expanded regions with low stacking energy, which cover most of the moiré cell, while unfavorable stackings shrink to form topological defects linked by a periodic network of domain walls. We find analytical expressions that successfully capture this strong-coupling regime for both the triangular soliton network and the honeycomb soliton network, matching predictions from lammps molecular dynamics simulations, and numerical solutions of continuum elasticity theory. We find an emergent universality for which the theory is characterized by a single twist-angle dependent parameter. Our formalism is essential to understand experiments on a wide-range of materials of current interest, including twisted bilayer graphene, both aligned and antialigned stacked twisted ${\mathrm{WSe}}_2$ and twisted ${\mathrm{MoTe}}_2$, and any other twisted homobilayer with the same stacking symmetry.

We prove an all-or-nothing theorem for all isotropic nearest-neighbor spin chains with arbitrary spin $S$: the system is either completely integrable (it has all $k$-local conserved quantities) or nonintegrable (it has no nontrivial local conserved quantity). This result excludes the possibility of an intermediate system with some but not all local conserved quantities, which solves in the affirmative the Grabowski-Mathieu conjecture. In addition, these two cases are decided by whether a single, easily computable quantity $D^3$ is zero or not. This theorem also serves as a complete classification of integrability and nonintegrability for $S\le 13.5$, suggesting that all the integrable models are exhausted by the Yang-Baxter solvable families.

Cloaking for bending waves propagating in thin elastic plates is known to present numerous obstacles to its experimental realization, particularly due to the complexity of the effective medium obtained by coordinate transformation. Here we demonstrate the possibility of cloaking in a unidirectional manner using affine transformations. This class of transformations maps the Kirchhoff-Love plate equation to its anisotropic extension. Unlike most publications in the literature, the resulting cloak is easily manufacturable using composite materials. In addition to numerical demonstrations of the unidirectional cloaking phenomenon, we present here a design method of an effective cloaking device, as well as the experimental validation of the manufactured cloak.

Lattice relaxation in twisted van der Waals materials is not merely a numerical nuisance; it is the mechanism that sets the electronic landscape. Here, we uncover how relaxation is generated and why it reshapes bands and topology. Starting from continuum elastic theory, we derive closed-form relaxation fields by minimizing intralayer elasticity energy and interlayer adhesion energy. We further introduce an analytical phase factor expansion theory that maps relaxation into the electronic Hamiltonian. The analysis identifies relaxation-induced gaugelike fields that control bandwidth suppression, band inversions, and valley Chern numbers. While our framework yields orders-of-magnitude speedup over supercell-based ab initio workflows, its central contribution is mechanistic: a unified, analytic description that predicts and interprets relaxation-driven band engineering in twisted systems such as twisted graphene and ${\mathrm{MoTe}}_2$. Furthermore, our framework interfaces naturally with many-body methods.

Recent studies have revealed that spin Hall magnetoresistance (SMR) contributes to both the anomalous and planar Hall resistances in nonmagnetic metal (NM)/ferromagnetic metal (FM) bilayers. This effect becomes pronounced when the NM layer exhibits a large spin Hall angle, as in W/CoFeB bilayers. In such systems the ratio of planar to anomalous Hall resistances, normally small in single CoFeB layers, can approach unity. This unusually large ratio complicates the determination of spin-torque efficiency using harmonic Hall voltage measurements. To overcome this limitation, magneto-optical Kerr effect (MOKE) measurements have been proposed as an alternative approach. Here, we investigate the polar and quadratic MOKE components, which correspond to, respectively, the anomalous and planar Hall resistances in the low-frequency limit, to clarify whether the MOKE measurements are suitable for characterizing the spin-torque efficiency. We find that the ratio of quadratic-to-polar MOKE signals in NM/FM bilayers is significantly smaller than the corresponding Hall resistance ratio, indicating that SMR contributes negligibly to the MOKE response in the visible range. Consequently, the spin-torque efficiency extracted from MOKE measurements agrees well with those expected from the spin Hall angle of the NM layer. These results clarify the reason why MOKE measurements provide reliable determination of the spin-torque efficiency.

Kagome metals with the formula $R{M}_6{X}_6$ ($R =\mathrm{rare}$ earth, $M =3\mathrm{d}$ transition metal, and $X =\mathrm{Sn}$/Ge) provide a rich platform for exploring magnetic and electronic phenomena, with tunable properties enabled by the combination of rare-earth elements and transition metals. In this study, we report the structural, electrical, and magnetic properties of kagome metal $\left(\mathrm{N}{\mathrm{d}}_x\mathrm{G}{\mathrm{d}}_{1-x}\right){\mathrm{V}}_6\mathrm{S}{\mathrm{n}}_6$. We demonstrate that substituting lighter Nd atoms at the Gd site tunes the complex magnetic ground state of $\mathrm{Gd}{\mathrm{V}}_6\mathrm{S}{\mathrm{n}}_6$ into a ferromagneticlike one. Moreover, the isotropic magnetization of $\mathrm{Gd}{\mathrm{V}}_6\mathrm{S}{\mathrm{n}}_6$ becomes anisotropic, with the $c$ axis emerging as the easy axis. Transport measurements reveal a strong coupling between magnetism and electronic properties, with negative magnetoresistance observed at low magnetic fields in all compositions. In addition, a fourfold anisotropy component tends to emerge in end compounds at higher magnetic fields. These findings highlight the role of rare-earth substitution in tuning magnetic anisotropy and magnetotransport behavior in $R{M}_6{X}_6$ compounds, featuring a nonmagnetic kagome layer, with potential implications for spintronic and topological applications.

Topological markers provide an efficient and powerful characterization of topological features of many systems, especially when the translation symmetry is broken. Recently, a universal topological marker applicable in different symmetry classes of topological systems is proposed. However, it suffers from irregular behaviors at the boundary and its connection to other topological indexes remains elusive. In this work, we construct regularized universal topological markers that apply to Dirac systems by utilizing position operators that are compatible with periodic boundary conditions. The regularized markers eliminate the obstructive boundary irregularities successfully and give rise to the desired global topological invariants, such as the Chern number, consistently when integrated over all the lattice sites. Furthermore, the regularized form allows us to establish an explicit connection between the markers and some other known topological indices in two dimensions. For instance, it turns out to be equivalent to the Bott index in classes A, D, and C and equivalent to the spin Chern number in classes DIII and AII. We further examine the utility and stability of this marker in disordered scenarios. We find that its variance shows peaks at the phase boundaries, which promotes it as a useful indicator for detecting disorder-induced topological phase transitions.

Pyrochlore magnets of the form $R_2{B}_2{\mathrm{O}}_7$, in which rare-earth ions on the $R$ site form a three-dimensional network of corner-sharing tetrahedra, provide a canonical setting for geometrical frustration. Ho-based pyrochlores host a dipolar spin-ice ground state, characterized by Ising moments constrained by the ice rules and elementary excitations analogous to magnetic monopoles. Here we examine how controlled chemical disorder influences this state by introducing site mixing on the nonmagnetic $B$ site in two compounds. ${\mathrm{Ho}}_2{\mathrm{GaSbO}}_7$ contains only ${\mathrm{Ga}}^{3+}/{\mathrm{Sb}}^{5+}$ charge disorder, whereas ${\mathrm{Ho}}_2{\mathrm{ScSbO}}_7$ exhibits both charge and substantial size disorder arising from the large ionic-radius mismatch between ${\mathrm{Sc}}^{3+}$ and ${\mathrm{Sb}}^{5+}$. Although both materials retain the pyrochlore structure, neutron-scattering measurements reveal a reduced correlation length for the $R/B$-site cation ordering and enhanced local structural distortions in ${\mathrm{Ho}}_2{\mathrm{ScSbO}}_7$. Despite these structural differences, bulk thermodynamic measurements and magnetic diffuse scattering demonstrate that both systems exhibit the defining signatures of a dipolar spin-ice state. Low-energy inelastic neutron spectroscopy further uncovers broad magnetic excitations that develop within the dipolar spin-ice regime, a feature absent in pristine Ho pyrochlores and indicative of disorder-induced splitting of the non-Kramers ground-state doublet. Together, these results show that controlled disorder generates tunable transverse-field-driven quantum fluctuations in Ho-based pyrochlores, although the dipolar spin-ice state is remarkably robust to this disorder.

Superconductivity has been observed for the 2D electron gas (2DEG) at the interface of ${\mathrm{KTaO}}_3$ with other oxides, with a transition temperature about an order of magnitude higher than its $3d$ cousin ${\mathrm{SrTiO}}_3$. The superconducting transition temperature is strongly dependent on the orientation of the interface. Motivated by this observation, we study pairing due to the exchange of the soft transverse optic phonon mode characteristic of quantum paraelectrics and use the resulting theory to comment on the nature of superconductivity of this 2DEG. We find (1) an orientation dependence consistent with experiment along with an anisotropic gap function, but (2) a BCS coupling constant that is smaller than needed and so must be augmented by contributions from other phonons to be consistent with the observed values of $T_c$.

A linear magnetoelectric (ME) response emerges when both space inversion and time-reversal symmetries are broken, enabling a symmetry-allowed coupling between electric and magnetic fields. In this work, a substantial linear ME coupling of up to 12%, accompanied by an unconventional glassy behavior in the dynamic ME response, is observed in the cluster-glass (CG) compound ${\mathrm{CuMn}}_2{\mathrm{O}}_4$. The CG state is identified through the frequency-dependent behavior of ac susceptibility, the memory effect in the relaxation of dc magnetization, and neutron depolarization measurements. Neutron diffraction confirms the absence of long-range magnetic order and reveals a structural transition to a polar $I{4}_{1}md$ phase from the high-temperature centrosymmetric $I{4}_1/amd$ phase, which is supported by the synchrotron x-ray diffraction as well as x-ray absorption spectroscopy. The emergence of this polar structure leads to ferroelectric ordering at the onset of the structural and CG transition. The concurrent observation of a static linear ME response and a glassy ME response in the CG state raises a fundamental question regarding the symmetry-driven ME coupling in disordered magnetic systems.

We investigated the lattice dynamics of quasi-two-dimensional Pd-intercalated ${\mathrm{ErTe}}_3$ in relation to its charge-density-wave (CDW) transitions by means of x-ray diffuse and meV-resolution inelastic x-ray scattering. In pristine ${\mathrm{ErTe}}_3$, CDW order develops at orthogonal in-plane wave vectors ${\mathrm{q}}_1^c=(0,0,0.29)$ (the $c\text{−}\mathrm{CDW}$) and ${\mathrm{q}}_2^a=(0.31,0,0)$ (the $a\text{−}\mathrm{CDW}$), with transition temperatures $T_1^c=270\mathrm{K}$ and $T_2^a=160\mathrm{K}$, respectively. Remarkably, we observe diffuse x-ray scattering already near the higher transition temperature $T_1^c$ along $a\text{−}\mathrm{CDW}$ but at a slightly different wave vector ${\mathrm{q}}_1^a=(0.29,0,0)$. Inelastic x-ray scattering for ${\mathrm{Pd}}_{0.01}{\mathrm{ErTe}}_3$ shows that a partial phonon softening at ${\mathrm{q}}_1^a$, underscoring the strong competition between ordering tendencies along the nearly equivalent in-plane axes of the orthorhombic lattice. For intercalation levels $x\ge 0.02$, the $a\text{−}\mathrm{CDW}$ state is suppressed. Nevertheless, a similar correlation between phonon softening and diffuse scattering persists along the [100] direction, again observed at ${\mathrm{q}}_1^a=(0.29,0,0)$ and $T_1^c$. These findings suggest that the $a\text{−}\mathrm{CDW}$ is fully suppressed for $x\ge 0.02$, and that the residual diffuse scattering at ${\mathrm{q}}_1^a$ originates from the partial phonon softening associated with the $c\text{−}\mathrm{CDW}$, reflected by the near equality of the absolute size of ${\mathrm{q}}_1^c$ and ${\mathrm{q}}_1^a$.

Reconstructing effective Hamiltonians of condensed matter systems directly from experimental data is challenging because of the intricate relationship between Hamiltonian parameters and observables. Here, we reconstruct an effective three-band electron-hole Hamiltonian in bulk GaAs based on high-order sideband generation (HSG) induced by quasicontinuous near-infrared (NIR) and terahertz (THz) lasers. We perform polarimetry of high-order sidebands while varying the wavelength and polarization of the NIR laser, as well as the strength of the THz field (27 to 64 kV/cm at 447 GHz). An analytic model is derived to incorporate the effects of both dephasing and quantum fluctuations around the semiclassical electron-hole recollision pathways. Surprisingly, the contribution of quantum fluctuations to the decay of sideband intensity with increasing sideband order is comparable to the contribution of dephasing. Assuming that the exciton reduced mass and the single parameter that defines the hole Bloch wave functions in bulk GaAs are known from previous experiments, we simultaneously and unambiguously determine through Bloch-wave interferometry the following: the effective Hamiltonian parameter that determines the electron-hole reduced masses, $\xi =0.125\pm 0.011$; the band gap of GaAs at 30 K, $E_{\mathrm{g}}=1.530\pm 0.001\mathrm{eV}$; and two dephasing constants associated with two electron-hole species, ${\mathrm{\Gamma }}_{\text{E-HH}}=10.4\pm 0.2\mathrm{meV}$ and ${\mathrm{\Gamma }}_{\text{E-LH}}=7.6\pm 0.2\mathrm{meV}$. We demonstrate that full Hamiltonian reconstruction can be achieved by combining HSG measurements with absorbance spectroscopy. Unexpectedly, we find that the extracted band gap of GaAs is about 10 meV larger than the value inferred from previous absorbance measurements. Quantum-kinetic analysis suggests that, in the HSG experiments, the electron-hole energy may be renormalized through Fröhlich interaction that is modulated by the strong THz fields. We also show that the energy threshold for optical-phonon emission can be suppressed by applying a strong THz field, leading to nearly constant dephasing rates. Our work provides an opportunity to explore possible modification of polaronic effects under strong THz fields. We show that polarimetry of high-order sidebands, together with interband absorption measurements, symmetry analysis, and analytic theory, can potentially enable reconstruction of effective Hamiltonians for other direct-gap insulators and semiconductors, whose bulk is not directly accessible to surface-sensitive techniques such as angle-resolved photoemission spectroscopy (ARPES).

The Berry connection encodes the momentum-space geometry of occupied Bloch states in gapped insulators and plays a central role in topological materials. While gauge-invariant quantities can be evaluated from overlap matrices between neighboring $k$ points, accessing the Berry connection itself as a smooth field requires specifying a continuous gauge over the Brillouin zone. Wannier-based workflows achieve this through projection onto localized orbitals, enabling stable evaluation of geometric quantities and response functions. In this setting, the Berry connection enters directly in Wannier-interpolated calculations of polarization, Berry curvature, and related response functions. In practical implementations, however, the projection-gauge Berry connection is typically constructed from finite-difference overlaps between neighboring $k$ points, discretizing momentum derivatives and introducing errors tied to $k$-mesh spacing and gauge alignment. These effects can become numerically delicate in systems with small band gaps or when evaluating higher-order responses such as the Chern-Simons axion angle. Here, we derive an exact expression for the non-Abelian Berry connection in the projection gauge that is local in crystal momentum. Starting from projected and orthonormalized Bloch-like states, we obtain a closed-form equation expressed entirely in terms of $k$-local quantities. We validate the formulation in one and three dimensions by computing the Berry phase and Chern-Simons axion angle in tight-binding models. The resulting framework provides a stable route to evaluating geometric properties within Wannier-interpolation schemes and future first-principles implementations.