Altermagnetism offers a unique potential for spintronic applications through its distinctive spin-split band structure and coupling to crystal symmetries. However, achieving electric-field control of spin and valley degrees of freedom remains a fundamental challenge. Here, we develop a spin-group theory framework to systematically identify symmetry conditions for spin-layer coupling in two-dimensional altermagnets. We classify magnetic layer groups that simultaneously support altermagnetism and valley-contrasting layer polarization, enabling electric-field-induced valley splitting and the spin Hall effect. Our predictions are verified by both tight-binding modeling and first-principles calculations on a ${\mathrm{VS}}_2$ bilayer, where a perpendicular electric field generates measurable valley polarization and spin Hall current. This work establishes a universal symmetry design principle for electrical control of spin-valley phenomena in altermagnetic materials.

The low-temperature properties of a two-dimensional Bose fluid of charged particles interacting through a $1/r$ potential, moving in the presence of a uniform neutralizing background, is studied by Quantum Monte Carlo simulations. We make use of the Modified Periodic Coulomb potential formalism to account for the long-range character of the interaction, and explore a range of density corresponding to average interparticle separation $1\le r_s\le 80$. We report numerical results based on simulations of a system comprising up to 2304 particles. We find a superfluid ground state for $r_s$ as large as 70, i.e., significantly above the most recent numerical estimate of the Wigner crystallization threshold. Furthermore, no thermally reentrant crystalline phase or any evidence of metastable bubbles are observed near the transition, in contrast with a previous theoretical study in which quantum statistics was neglected. Altogether, the computed superfluid transition temperature depends remarkably weakly on density.

Multinary hydrides offer great promise for achieving high-temperature conventional superconductivity under ambient pressure. However, the rich variety of structural configurations in hydrides poses a formidable challenge for searching their immense phase space. In this work, we used our developed artificial intelligence (AI) search engine (InvDesFlow) to perform extensive investigations regarding ambient stable superconducting hydrides. We assessed the thermodynamic stability of hydrides by our AI model. For ${\mathrm{K}}_2{\mathrm{GaCuH}}_6$, the AI-predicted formation energy difference along the synthesis path is 0.146 eV/atom, closely matching the density functional theory result of 0.137 eV/atom. This agreement confirms the thermodynamic stability of hydrides and validates the reliability of AI method. Several quaternary hydrides with high superconducting temperature ($T_c$) are predicted. In particular, the superconducting $T_c$ of ${\mathrm{K}}_2{\mathrm{GaCuH}}_6$ and ${\mathrm{K}}_2{\mathrm{LiCuH}}_6$ are calculated to be 68 and 53 K under ambient pressure, respectively, which shows a significant enhancement in comparison with that of ${\mathrm{K}}_2{\mathrm{CuH}}_6$ ($T_c\sim 18\text{K}$). We also find that intercalating atoms could cause phonon softening and induce more phonon modes with strong electron-phonon coupling. Hence, we propose that intercalating atoms is a feasible approach in searching for superconducting quaternary hydrides.

Noncentrosymmetric superconductors provide a unique platform to explore the interplay of antisymmetric spin-orbit coupling and pairing symmetry. In this study, we report the synthesis and comprehensive characterization of the noncentrosymmetric ternary $\alpha$-Mn compound ${\mathrm{NbTaOs}}_2$ using electrical resistivity, magnetization, specific heat, and muon spin rotation/relaxation ($\mu \mathrm{SR}$). It confirms that ${\mathrm{NbTaOs}}_2$ is a type-II bulk superconductor. Transverse-field $\mu \mathrm{SR}$ and specific-heat data consistently indicate a moderately coupled, fully gapped superconducting state.

It has recently become clear that phonons generate a sizable thermal Hall effect in cuprates, whether they are undoped, electron-doped or hole-doped (inside the pseudogap phase). At higher doping, where cuprates are reasonably good metals, mobile electrons also generate a thermal Hall effect, the thermal equivalent of the standard electrical Hall effect. Here we show that in the cleanest crystals of the electron-doped cuprate ${\mathrm{Nd}}_{2-x}{\mathrm{Ce}}_x{\mathrm{CuO}}_4$, at high doping, the phonon and electron contributions to the thermal Hall conductivity ${\kappa }_{\mathrm{xy}}$ are of comparable magnitude, but of opposite sign. In samples of lower quality, phonons dominate ${\kappa }_{\mathrm{xy}}$, resulting in a negative ${\kappa }_{\mathrm{xy}}$ at all temperatures. The fact that the negative phononic ${\kappa }_{\mathrm{xy}}$ in the metallic state is similar in magnitude and temperature dependence to that found in the insulating state at lower doping rules out any mechanism based on skew scattering of phonons off charged impurities, since a local charge should be screened in the metallic regime. The phononic ${\kappa }_{\mathrm{xy}}$ is found to persist over the entire doping range where antiferromagnetic correlations are known to be significant, suggesting that such correlations may play a role in generating the phonon thermal Hall effect in electron-doped cuprates. If the same mechanism is also at play in hole-doped cuprates, the presence of a phononic ${\kappa }_{\mathrm{xy}}$ below (and only below) the critical doping $p^{★}$ would be evidence that spin correlations are a property of the pseudogap phase.

The optical and magneto-optical properties of thin epitaxial Ni-Mn-Ga films, with thicknesses ranging from 8 to 160 nm, were investigated across the spectral range of 0.7–6.4 eV. The films were deposited by dc magnetron sputtering on MgO (100) substrates with a stress-mediating Cr buffer layer. Structural and magnetic characterization revealed a stress-induced martensitic transformation for the films thicker than 80 nm, while thinner films remained in an austenite structure due to the substrate constraint. In martensitic samples, a mixture of 14M and NM phases was observed with both X-type and Y-type twin domains. Magneto-optical polar Kerr effect spectra showed a notable evolution with film thicknesses, demonstrating changes in the electronic structure of Ni-Mn-Ga. A combination of spectroscopic ellipsometry and magneto-optical Kerr spectroscopy allowed for the deduction of the spectral dependence of the full permittivity tensor of the investigated samples. Three magneto-optical transitions were fitted to the spectra of nondiagonal permittivity using semiclassical theory, showing strong correlations with in-plane coercivity. Observed correlations highlight the impact of substrate-induced stress on Ni-Mn-Ga films and provide insights into the electronic structure changes associated with the martensitic transformation.

We study the effect of the Dzyaloshinskii-Moriya interaction (DMI) on the nonlinear creation of spin-wave harmonics. We analyze the Landau-Lifshitz equations, numerically and analytically, for a narrow Permalloy stripe with interfacial DMI. If the static field is perpendicular to the stripe, spin waves traveling in one direction can have harmonics that are more than 50 times larger than that for the waves moving oppositely. When the external field is parallel to the stripe and the DMI is present, both even and odd harmonics are generated; without the DMI, only odd harmonics appear. This potentially offers a different way to measure the DMI strength. In systems with larger nonlinearity, through an increased driving field or a different choice of driving frequency, frequency combs can appear.

For all collinear altermagnets, we sort out piezomagnetic free-energy invariants allowed in the nonrelativistic limit and relativistic piezomagnetic invariants bilinear in the Néel vector $\mathbf{L}$ and magnetization $\mathbf{M}$, which include strain-induced Dzyaloshinskii-Moriya interaction. The symmetry-allowed responses are fully determined by the nonrelativistic spin Laue group. In the nonrelativistic limit, two distinct mechanisms are discussed: the band-filling mechanism, which exists in metals and is illustrated using the simple two-dimensional Lieb lattice model, and the temperature-dependent exchange-driven mechanism, which is illustrated using first-principles calculations for transition-metal fluorides. The leading second-order nonrelativistic term in the strain-induced magnetization is also obtained for CrSb. Piezomagnetism due to the strain-induced Dzyaloshinskii-Moriya interaction is calculated from first principles for transition-metal fluorides, MnTe, and CrSb. Finally, we discuss triplet superconducting correlations supported by altermagnets and protected by inversion rather than time-reversal symmetry. We apply the nonrelativistic classification of Cooper pairs to describe the interplay between strain and superconductivity in the two-dimensional Lieb lattice and in bulk rutile structures. We show that triplet superconductivity is, on average, unitary in an unstrained altermagnet, but becomes nonunitary under piezomagnetically active strain.

We investigate the ground-state nature of the honeycomb Kitaev-$\mathrm{\Gamma }$ model in the material-relevant parameter regime through a combination of analytics and classical and quantum simulations. We find the classical model is imprinted with a tangle of highly structured spin double helices. This helix tangle consists of 18 inequivalent helices and features modulation of multiple rotation axes, an anisotropy in spacial periodicities indicative of spontaneous symmetry breaking, and a $\mathrm{sgn}\left(\mathrm{\Gamma }\right)$-determined chirality pattern. Infinite projected entangled pair state simulations with clusters of up to 36 sites identify hallmarks of this unprecedented many-body order in the quantum spin-$1/2$ model. Our findings provide a fresh perspective of the Kitaev-$\mathrm{\Gamma }$ model and enrich the physics of the Kitaev magnetism.

Inverted hysteresis loops (IHLs) exhibiting negative coercivity and remanence represent a counterintuitive phenomenon in magnetic systems, with origins remaining elusive. Here, we address this long-standing paradox through combined experimental and theoretical investigations of two prototypical heterostructures: a metallic exchange-spring system (NiFe/CoFeB/MgO) and a hybrid ferromagnetic semiconductor-topological insulator ($\mathrm{M}{\mathrm{n}}_x\mathrm{G}{\mathrm{e}}_{1-x}/\mathrm{B}{\mathrm{i}}_2\mathrm{S}{\mathrm{e}}_3$). In the former, complete IHLs occur under out-of-plane fields, accompanied by unprecedented asymmetric angular dependence of remanence, a hallmark of noncollinear magnetic configurations. Our minimal bilayer model reveals that such anomalous hysteresis universally originates from the interfacial nonlinear spin configurations induced by the synergistic effect of inhomogeneous magnetic parameters and antiferromagnetic exchange coupling, where IHL becomes energetically stabilized only when the interlayer coupling strength exceeds a critical threshold. Guided by this principle, we engineered the latter system, where $\mathrm{B}{\mathrm{i}}_2\mathrm{S}{\mathrm{e}}_3$'s spin texture couples antiferromagnetically with $\mathrm{M}{\mathrm{n}}_x\mathrm{G}{\mathrm{e}}_{1-x}$'s magnetization, observing temperature-robust IHLs from 10 K to 250 K. Crucially, energy analysis demonstrates that the apparent “negative coercivity” corresponds to a metastable minimum in the free-energy landscape, reconciling IHLs with fundamental thermodynamic laws. This work establishes interfacial coupling as a universal design rule for manipulating hysteresis topology, offering direct implications for spin-orbit torque devices and topological spintronic applications.

Electron-phonon coupling is believed to be responsible for many spectral anomalies in the cuprate superconductors. In particular, the $B_{1g}$ buckling mode of the oxygen ion in the ${\text{CuO}}_2$ plane has been proposed to be responsible for the dramatic peak-dip-hump (PDH) structure in the antinodal spectrum. The recent observation of the exceptional flat quasiparticle dispersion in the antinodal region and the sudden suppression of the PDH structure around the pseudogap end point cast doubts on such a scenario. Instead, a scenario involving the coupling to the antiferromagnetic spin fluctuation seems to resolve both puzzles naturally. Here, we present a systematic study on the interplay between antiferromagnetic spin fluctuation and electron-phonon coupling in the cuprate superconductors and their respective roles in the origin of the PDH structure. We show that the coupling strength to the $B_{1g}$ buckling mode is strongly renormalized by the vertex correction caused by the antiferromagnetic spin fluctuation. In particular, the coupling strength to the $B_{1g}$ buckling mode is strongly suppressed in the $\mathbf{q}\to 0$ limit as a result of the destructive interference between electron-phonon coupling at electron momentum differ by the antiferromagnetic wave vector. Counterintuitively, we find that the same vertex correction enhances the phonon contribution to the PDH structure as a result of its highly anisotropic momentum dependence around $\mathbf{q}=0$. We also find that while the coupling to either the antiferromagnetic spin fluctuation or the $B_{1g}$ buckling mode can generate a PDH structure in the antinodal spectrum with similar phenomenologies, the sudden suppression of such a structure around the pseudogap end point should be mainly attributed to the dramatic change in the nature of the spin fluctuation at such a critical doping. We suggest to take the PDH structure in the antinodal spectrum as a spectral signature for the emergence of fluctuating local moment in the pseudogap phase and the entrance of a doped Mott insulating state.

Using density functional theory calculations, we investigate the microscopic origins of the distinct ground states in monolayer $T\text{−}{\mathrm{VSe}}_2$ and $H\text{−}{\mathrm{VSe}}_2$. We reveal that $T\text{−}{\mathrm{VSe}}_2$ exhibits competing tendencies towards either ferromagnetic (FM) or charge density wave phases, governed by the Fermi surface nesting in the weak-coupling limit. In contrast, $H\text{−}{\mathrm{VSe}}_2$ stabilizes a robust FM ground state within the local moment picture of the strong-coupling limit. The dichotomy originates from contrasting correlation strengths due to distinct orbital degrees of freedom controlled by the crystal field splittings between $T\text{−}{\mathrm{VSe}}_2$ and $H\text{−}{\mathrm{VSe}}_2$. We argue similar physics can also be applied to ${\mathrm{VS}}_2$ and ${\mathrm{VTe}}_2$ in the T and H phases. While triply degenerate $t_{2g}$ orbitals with a larger bandwidth favor the itinerant scenario in the weak-coupling limit in the T phase, a nondegenerate $d_{z^2}$ orbital with a narrower bandwidth supports the local moment picture in the strong-coupling limit in the H phase. Furthermore, we demonstrate the tunability of these states via Se height, offering pathways to manipulate quantum phases in $T\text{−}{\mathrm{VSe}}_2$. This work provides a comprehensive understanding of various conflicting experimental findings and theoretical predictions regarding polymorphic monolayer ${\mathrm{VSe}}_2$.

We provide a systematic formula, in terms of integer partitions, that generates perturbation theory explicitly at an arbitrary order. Our approach naturally includes an infinite number of perturbations and uses a single matrix equation that contains the information for both the eigenvalue and eigenvector corrections. The formula reduces to the standard case of one perturbation in the appropriate limit. This formulation streamlines the derivations that are traditionally tedious in perturbation theory, facilitating high-order calculations.

We conducted small-angle neutron scattering (SANS) experiments on the ferromagnetic semimetal ${\mathrm{EuB}}_6$, where we observed first-hand evidence for the presence of magnetic polarons. We carried out SANS experiments over a large range of scattering vectors $|\vec{\mathbf{q}}|$, ranging from 0.006 to 0.140 ${\AA }^{-1}$ , and temperatures of 2 to 60 K. Just above $T_{\mathrm{C}}$ our experiments show magnetic scattering intensity, which has a Lorentzian dependence on the wave vector, characteristic of the presence of magnetic polarons. Below $T_{\mathrm{C}}$ the polarons merge, and most of the observed intensity is due to scattering from domains. We were able to extract a correlation length $\xi$ that ranges from 100 to 300 Å for the size of the magnetic polarons. This size is much larger than one would expect for magnetic fluctuations of a three-dimensional Heisenberg ferromagnet, demonstrating the influence of magnetic polarons on the phase transition.

The Zeeman effect, induced by the magnetic field, which can break the Dirac edge states of first-order topological insulators to generate a nontrivial gap, is a physical mechanism for the realization of two-dimensional second-order topological insulators (SOTIs). However, such magnetic-field-driven SOTIs have not yet been experimentally affirmed, and candidate systems in naturally available materials remain scarce. Herein, combining first-principles calculations and effective model analysis, we propose a design strategy to achieve the SOTIs in van der Waals heterobilayers by utilizing the interlayer couplings and out-of-plane magnetic fields. This is different from the previous in-plane magnetic field mechanism. Moreover, we have uncovered that two distinct types of heterobilayers can exhibit the nature of SOTIs, characterized by the shifted Dirac cone, gapped edge states, real-space zero-dimensional corner states, and topological invariants. Our findings not only expand the design avenues of magnetic SOTIs from in-plane to out-of-plane cases but also establish a practical materials framework for the experimental detection of the SOTI phase.

We theoretically investigate the electron tunneling in dual-gated bilayer graphene-based $n/p$ junctions. It is shown that a band gap is introduced by tuning the gate voltage, which modifies the pseudospin polarization and breaks anti-Klein tunneling at normal incidence. Specifically, when the pseudospin polarization vectors for the propagating and evanescent wave modes on the left and right regions of the junction are orthogonal, a revival of Klein tunneling is achieved. The Berry phase associated with Klein tunneling in dual-gated bilayer graphene is not limited to $\pi$ but varies with the junction parameters. Furthermore, the Klein tunneling is accompanied by a $\pi$ jump in the reflection phase around the normal incidence.

The complex valence band structure of bulk cuprous oxide necessitates going beyond the parabolic approximation to precisely estimate exciton binding energies. The same is true for excitons in cuprous oxide quantum wells, for which many effects have been obtained so far only qualitatively within a hydrogenlike two-band model. Here, we derive the complete Hamiltonian for excitons in cuprous oxide quantum wells based on the Luttinger-Kohn model, taking into account the full complex valence band structure. Symmetry properties of the system are discussed. Numerical results based on the diagonalization of the Hamiltonian using B-spline functions reveal the energy shifts and the lifting of degeneracies due to the nondiagonal coupling terms of the complex valence band. The relative oscillator strengths of the excitonic transitions induced by circularly polarized light are also calculated.

We explore the states of matter arising from the spontaneous symmetry breaking (SSB) of ${\mathbb{Z}}_2$ non-onsite symmetries. In one spatial dimension, we construct a frustration-free lattice model exhibiting SSB of a non-onsite symmetry, which features the coexistence of two ground states with distinct symmetry-protected topological (SPT) orders. We analytically prove the twofold ground-state degeneracy and the existence of a finite-energy gap. Fixing the symmetry sector yields a long-range entangled ground state that features long-range correlations among noninvertible charged operators. We also present a constant-depth measurement-feedback protocol to prepare such a state with a constant success probability in the thermodynamic limit, which may be of independent interest. Under a symmetric deformation, the SSB persists up to a critical point, beyond which a gapless phase characterized by a conformal field theory emerges. In two spatial dimensions, the SSB of 1-form non-onsite symmetries leads to a long-range entangled state (SPT soup)—a condensate of one-dimensional SPT along any closed loops. On a torus, there are four such locally indistinguishable states that exhibit algebraic correlations between local operators, which we derived via a mapping to the critical $O\left(2\right)$ loop model. This constitutes an intriguing example of ‘‘topological quantum criticality.’’

Developing reliable pseudopotentials for orbital-free density functional theory (OF-DFT), especially for transition metals, remains a significant challenge. In this study, we provide a theoretical framework for analyzing pseudization strategies for OF-DFT calculations. From the analysis arises a proposed pseudization method which involves constructing local pseudopotentials by targeting existing Kohn-Sham DFT pseudopotentials through an optimized effective potential procedure. We produce four distinct sets of local pseudopotentials and evaluate their accuracy and transferability on the set of transition metal elements. Our results indicate a substantial improvement over previously available pseudopotentials. Although current OF-DFT functionals still only reach a qualitative accuracy for transition metals, our newly developed pseudopotentials provide a rigorous framework for further methodological advancements.

Recently, there has been considerable excitement surrounding the promising realization of high-spin Kitaev material, such as the quasi-2D compound ${\mathrm{CrI}}_3$ and ${\mathrm{CrGeTe}}_3$. However, the stability of quantum spin liquids (QSL) against single-ion anisotropy (SIA) in these materials and the global quantum phase diagram of the extended spin-3/2 Kitaev model with finite SIA remain unclear. In this study, we perform large-scale density matrix renormalization group (DMRG) to explore the quantum phase diagram of the generalized spin-3/2 Kitaev-Heisenberg (K-H) model accompanied with SIA $A_c$. In the $A_c=0$ limit, the spin-3/2 K-H model exhibits a quantum phase diagram similar to that of a spin-1/2 system, including two QSLs around antiferromagnetic and ferromagnetic Kitaev models. For models with finite $A_c$, we map out the quantum phase diagram around two Kitaev points and observe distinct types of in-plane vortex orders developed from these two QSL phases. Interestingly, a series of nearly degenerate vortex configurations is discovered in each vortex phase. Using linear spin-wave theory, we demonstrate that these vortex configurations can be understood as a consequence of the quantum correction on a continuous family of degenerate classical states.