In twisted bilayer graphene, a unified understanding of the mechanisms governing temperature-dependent electronic spectra and thermodynamic properties remains controversial despite extensive theoretical efforts. Here, we present a comprehensive theoretical framework that quantitatively accounts for scanning tunneling spectroscopy, quantum twisting microscopy, and thermodynamic properties of magic angle twisted bilayer graphene. We demonstrate that the observed behavior arises from the interplay between electron correlations and external symmetry breaking induced by strain and lattice relaxation. These effects act cooperatively to shape the emergent electronic behavior, leaving characteristic signatures across spectroscopy, compressibility, and entropy.

A highly exotic phenomenon in solid-state physics is the observation of magnetic quantum oscillations in insulators. For instance, in the Kondo insulator ${\mathrm{YbB}}_{12}$ various groups reported the observation of such oscillations seemingly originating from Fermi surfaces, though this contradicts the concept of an insulator having no charged quasiparticles. In this study, we searched for quantum oscillations in ${\mathrm{YbB}}_{12}$ by using bulk-sensitive ultrasonic experiments in high magnetic fields up to 65 T and down to 485 mK. For that, we utilized an ${\mathrm{YbB}}_{12}$ single crystal that, in previous experiments, revealed oscillations in the magnetoresistance in the insulating state. We confirmed oscillationlike behavior of the magnetoresistance as well as field-dependent oscillations in the magnetocaloric effect. However, we could not observe magnetoacoustic quantum oscillations in the insulating state, only in the field-induced metallic state. In the insulating state, we found some anomalies in our ultrasound data, the origin of which remains elusive. Our findings provide further information on the puzzling behavior of the insulating state of ${\mathrm{YbB}}_{12}$.

We propose a variational alternative to the Trotter-Suzuki decomposition that provides greater control over errors while preserving the unitary structure of time evolution. The variational parameters in our ansatz are derived from a global action principle, where Euler-Lagrange equations govern their optimal dynamics. Unlike conventional wavefunction-based variational methods, our approach specifically targets the time evolution operation, and this allows a single set of optimized parameters to be applied to any initial state for a fixed Hamiltonian avoiding costly optimization procedures. Our method outperforms the standard Trotter-Suzuki formulas, typically achieving higher accuracy than higher-order Suzuki schemes. This translates directly to quantum computing applications, where it enables the design of quantum circuits with fewer gates, which reduces noise and improves precision. Although we focus on quantum dynamics, the method is broadly applicable to problems involving general time-evolution operators. Applied to various model Hamiltonians, our approach reduces errors by factors of 2 to 5 compared to Trotter-Suzuki decompositions, demonstrating its promise for accurate quantum simulation with improved efficiency. In certain cases, the variational ansatz achieves higher accuracy than more complex higher-order Suzuki formulas while reducing the gate count by nearly half within a single circuit layer. Furthermore, we derive approximate analytical expressions for the variational parameters up to cubic order in time, valid for generic Hamiltonians. These approximations enable long-time quantum simulations with improved accuracy over equivalent Suzuki decompositions, providing ready-to-use evolution formulas that match Suzuki's gate complexity while delivering better performance.

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.