The development of Kondo lattice coherence in ${\mathrm{UTe}}_2$ leads to the formation of a heavy Fermi-liquid state from which superconductivity emerges at lower temperature. In Kondo lattice systems, the nuclear magnetic resonance (NMR) and muon (${\mu }^{+}$) Knight shift have proven to be particularly sensitive to the properties of the developing heavy-electron fluid. Here we report ${\mu }^{+}$ Knight shift measurements on high-quality ${\mathrm{UTe}}_2$ single crystals grown by a molten salt-flux method. Together with previous data from a single crystal grown by a chemical-vapor transport method, our results show the contribution of the heavy-electron liquid to the ${\mu }^{+}$ Knight shift increases below a crossover temperature $T^{*}\sim 30$ K in accord with a universal scaling function of $T/T^{*}$ for heavy-fermion materials. An observed departure from this universal scaling below a temperature $T_{\mathrm{r}}\sim 12$ K at certain ${\mu }^{+}$ stopping sites signifies a reversal of the Kondo hybridization and a relocalization of U $5f$ moments with an antiferromagnetic coupling. The preservation of universal scaling at a different ${\mu }^{+}$ site demonstrates a coexistence of itinerant and localized $5f$ electron states preceding the superconducting phase transition.

A general principle of condensed matter physics prohibits the electric current in equilibrium. This prevents a zero-resistance state realized solely under a finite electric current, namely unidirectional superconductivity. In this Letter, we propose a setup to realize the unidirectional superconductivity as a nonequilibrium steady state. We focus on the in-plane transport of atomically thin bilayer superconductors lacking in-plane inversion symmetry and introduce dissipation by applying the out-of-plane electric field and current. By analyzing time-dependent Ginzburg-Landau equations, we show that locally stable steady-state solutions appear only under an in-plane supercurrent when the out-of-plane electric field exceeds a threshold value. Our system also realizes a dissipation-induced superconducting diode effect up to $100\%$ efficiency by purely electric means.

Interatomic hopping mediated by spin-orbit coupling (SOC) entangles spin, orbital, and sublattice degrees of freedom of electrons, leading to the emergence of intriguing phenomena such as novel topological insulators and exotic spin-dependent transport including chirality-induced spin selectivity (CISS). Despite these effects, a comprehensive microscopic formalism to describe the spin-dependent hopping remains insufficiently established. In this study, we systematically investigate SOC hopping by analytically deriving the hopping integrals within a two-center approximation based on atomic orbitals. Introducing independent parameters, or extended Slater-Koster symbols, that characterize SOC hopping, we explicitly determine the form of the hopping for $s$, $p$, and $d$ orbitals in the arbitrary hopping directions. Our formalism is then implemented in tight-binding models on several lattices. Furthermore, we examine the effect of SOC on band dispersion by employing a multipole decomposition for the SOC Hamiltonian, providing a fundamental understanding of SOC-induced phenomena. In particular, we derive an explicit expression for the SOC Hamiltonian that causes unique spin splitting in chiral systems by considering a triangular helical chain. Most importantly, the obtained SOC Hamiltonian does not contain a term that has the symmetry of electric toroidal monopole $G_0$ but rather an electric toroidal quadrupole $G_u$, which is the origin of chirality in this case.

Obstacles in physical space produce a characteristic signature in the scattered field when exposed to incident waves, enabling their active or passive localization from field measurements. In waveguides, obstacles can be inhomogeneities such as cross-section variations or side branches. Such geometric perturbations cause reflections and absorption of traveling waves in the channel, decreasing their signal strength in the propagation direction and scattering waves back towards the sender. To mask these effects, we present a nondispersive method which can completely compensate losses incurred by absorption while simultaneously canceling reflections. It is based on the synchronization of outgoing waves from self-oscillations in the obstacle with the incident waves, and illustrated with an acoustic experiment. The latter is based on the use of a police whistle attached to the obstacle in a one-dimensional waveguide, causing a pure whistling tone whose energy can be harnessed via synchronization with a sufficiently strong and in-tune incident wave. An analytical model for the proposed nonlinear mechanism is derived and validated by experiments. The proposed quasipassive, all-acoustic concept has direct applications in acoustic metamaterials for cloaking and may be translated to electromagnetic and photonic applications with saturable gain elements.

$A{\mathrm{Ti}}_3{\mathrm{Bi}}_5$ ($A=$ Cs or Rb) are emerging topological kagome metals that exhibit superconductivity and nematicity without intertwining translational symmetry-breaking charge orders. In this work, we explore the fermiology of their titanium kagome electrons and identify a set of sublattice-pure, high-order van Hove singularities (VHSs) that can suppress charge ordering and enhance electronic correlations and superconductivity. Our calculations of charge susceptibility for kagome bands with both normal and high-order VHSs emphasize the role of these VHSs in driving electronic nematicity in ${\mathrm{CsTi}}_3{\mathrm{Bi}}_5$. Additionally, we compute the phonon spectrum and electron-phonon interactions for ${\mathrm{CsTi}}_3{\mathrm{Bi}}_5$ under pristine, doped, and kagome-exposed surface conditions, revealing its robustness against structural instabilities while enhancing the superconducting transition temperature. Our work positions $A{\mathrm{Ti}}_3{\mathrm{Bi}}_5$ as a key platform for investigating superconductivity and electronic nematicity without translational symmetry-breaking states in kagome metals.

Using variable temperature total x-ray scattering, we study the emergence of charge density wave (CDW) order in the archetypal transition-metal dichalcogenide (TMDC) $1T\text{−}{\mathrm{VSe}}_2$. We find that a CDW precursor phase (PF) appears at $T_{\mathrm{CDW}\left(\mathrm{PF}\right)}$ of 200(5) K, where V and Se atoms experience in- and out-of-plane static displacements from their position in the undistorted lattice, respectively. The displacements increase with decreasing temperature and a little-known superstructure of V triatomic clusters emerges below $T_{\mathrm{CDW}\left(3\mathrm{D}\right)}$ of 100(5) K, where three-dimensional CDW order sets in. Concurrently, Se atoms form less well-defined dimers. Thus, similarly to other TMDCs, $1T\text{−}{\mathrm{VSe}}_2$ appears to exhibit a two-step CDW transition. The finding underlines the key contribution of lattice distortions to the emergence of CDW order in $1T\text{−}{\mathrm{VSe}}_2$ and generally in TMDCs.

The intermetallic compound ${\mathrm{Fe}}_{1-x}{\mathrm{Co}}_x\mathrm{Si}$ exhibits helical magnetic order for $0.05<x<0.8$, whereas its orbital angular momentum, which contributes to the occurrence of the Dzyaloshinskii-Moriya (DM) interactions, has not yet been verified systematically. According to previous neutron experiments, the magnitude of the DM interaction has the maximum at around $x=0.25$, and that for $x=0.50$ was approximately 60% of that for $x=0.25$. We conducted soft x-ray magnetic circular dichroism spectroscopy on the Fe $L_{2,3}$ and Co $L_{2,3}$ edges below the critical temperature $T_{\mathrm{c}}$ for $x=0.50$ in addition to a previous experiment for $x=0.25$, and compared the ratios of their orbital ($m_{\text{orb}}$) and spin ($m_{\text{spin}}$) magnetic moments, evaluated independently for Fe and Co, for $x=0.25$ and 0.50. The values of $m_{\text{orb}}/m_{\text{spin}}$ were independently estimated as (1) 3% for Fe and 9% for Co at $x=0.25$ and (2) 3% for Fe and 11% for Co at $x=0.50$. Thus, the $m_{\text{orb}}/m_{\text{spin}}$ ratios for Fe and Co were almost independent of $x$. The present results reveal that the DM interaction in ${\mathrm{Fe}}_{1-x}{\mathrm{Co}}_x\mathrm{Si}$ originates from the orbital angular momentum of Fe.

A novel collinear magnetic phase, termed “altermagnetism,” has recently been uncovered, characterized by zero net magnetization and momentum-dependent collinear spin splitting. To understand the intriguing physical effects of altermagnets and explore their potential applications, it is crucial to analyze both the geometric and spin configurations of altermagnetic Fermi surfaces. Here, we conduct a comprehensive study of the quasiparticle interference (QPI) effects induced by both nonmagnetic and magnetic impurities in metallic altermagnets, incorporating the influence of Zeeman splitting and spin-orbit coupling. By examining the QPI patterns for various spin polarizations of magnetic impurities and different spin-probe channels, we identify a series of distinctive signatures that can be used to characterize altermagnetic Fermi surfaces. These predicted signatures can be directly compared with experimental results obtained through spin-resolved scanning tunneling spectroscopy.

We present a computational framework that combines dynamical mean-field theory (DMFT) with density functional theory (DFT) and the nonequilibrium Green's function (NEGF) technique to study the steady-state transport properties of magnetic tunnel junctions (MTJs). The objective of our calculations is then to understand the impact of dynamical electron correlations on the Fe $3d$ orbitals of an Fe/MgO/Fe system. By applying the rigid shift approximation, we study both the zero- and finite-bias properties in a simple and computationally efficient manner, obtaining the bias-dependent electronic structure, the current-versus-voltage characteristic curve in both the parallel and antiparallel configurations, and consequently, the tunneling magnetoresistance (TMR) ratio. We find that dynamical electron correlation manifests as a reduction in the spin splitting of the Fe $3d_{z^2}$ state compared to DFT predictions and introduces a finite relaxation time. The impact of these effects on transport, however, varies significantly between magnetic configurations and applied bias voltages. In the parallel configuration, the characteristic curves obtained with DFT and DMFT are similar up to large biases, as the transport is mostly due to the coherent transmission of spin-up electrons through the MgO barrier. Conversely, in the antiparallel configuration, correlation effects become more significant as the bias increases, with DMFT predicting a sharp current increase due to bias-driven inelastic electron-electron scattering. At zero bias, both DMFT and DFT similarly overestimate the TMR ratio compared to experiments. However, at finite bias, DMFT predicts a lower bias threshold for the suppression of the TMR relative to DFT, improving the agreement with experimental data and underscoring the importance of dynamical correlation effects on finite-bias behavior. While these conclusions are specific to Fe/MgO/Fe MTJs, our computational approach can be applied to other MTJs as well, thereby advancing the use of DMFT in spintronics.

Recently, it has been revealed that a variety of novel phenomena emerge in hyperbolic spaces, while non-Hermitian physics has significantly enriched the landscape of condensed matter physics. Building on these developments, we construct a geodesic-based method to study the non-Hermitian skin effect (NHSE) in nonreciprocal hyperbolic lattices. Additionally, we develop a geodesic-periodic boundary condition (geodesic-PBC), akin to the Euclidean periodic boundary condition (PBC), that complements its open boundary condition. Importantly, we find that the nonreciprocal directionality within a hyperbolic regular polygon and the geodesic-based boundary determine the spectral sensitivity, and hence, the NHSE. Unlike in Euclidean models, however, we must utilize boundary localization to distinguish nontrivial skin modes from their trivial boundary counterpart due to the extensive boundary volume of hyperbolic lattices. We also relate the spatial density profile with the finite-size scaling of hyperbolic lattices. These aspects highlight the profound impact of hyperbolic geometry on non-Hermitian systems and offer new perspectives on the intricate relationship between the geometric characteristics of hyperbolic lattices and non-Hermitian physics.

The energy-momentum dispersion of magnons, as collective low-energy excitations of a magnetic material, is routinely computed from an effective quantum spin Hamiltonian but simplified via linearized Holstein-Primakoff transformations to describe noninteracting magnons. The dispersion produced by such linear spin wave theory (LSWT) is then plotted as “sharp bands” of infinitely long-lived quasiparticles. However, magnons are prone to many-body interactions with other quasiparticles—such as electrons, phonons, and other magnons—which can lead to shifting (i.e., band renormalization) and broadening of the sharp bands as a signature of a finite quasiparticle lifetime. The magnon-magnon interactions can be particularly important in antiferromagnets, and, therefore, possibly in newly classified altermagnets sharing many features of collinear antiferromagnets. Here, we employ nonperturbative quantum many-body calculations via time-dependent matrix product states (TDMPSs) to obtain the magnon spectral function for a ${\mathrm{RuO}}_2$ altermagnet whose effective quantum spin Hamiltonian is put onto a four-leg cylinder. Its upper band is shifted away from the upper sharp band of LSWT, as well as broadened, which is explained as the consequence of hybridization of the latter with the three-magnon continuum. This implies that two-magnon Raman scattering spectra cannot be computed from LSWT bands, which offers a litmus test for the relevance of magnon-magnon interactions. Finally, we employ atomistic spin dynamics (ASD) simulations based on the classical Landau-Lifshitz-Gilbert (LLG) equation to obtain the magnon spectrum at finite temperature and/or at a fraction of the cost of TDMPS calculations. Despite including magnon-magnon interactions via the nonlinearity of the LLG equation, ASD simulations cannot match the TDMPS-computed magnon spectrum, thereby signaling nonclassical effects harbored by antiferromagnets and altermagnets.

Recently, the possibility of high-temperature superconductivity (SC) in flat band (FB) systems has been the focus of a great deal of activity. This Letter reveals that unlike conventional intraband SC for which disorder has a dramatic impact, that associated with FBs is surprisingly robust to disorder-induced fluctuations and quasiparticle localization. In particular, for weak off-diagonal disorder, the critical temperature decreases linearly with disorder amplitude for conventional SC, whereas it is only quadratic in the case of SC in FBs. Our findings could have a major impact on the research and development of new compounds whose high purity will no longer be a critical barrier to their synthesis.

Ultrathin magnetic films on heavy metal substrates with strong spin-orbit coupling provide versatile platforms for exploring novel spin textures. So far, structurally open fcc(110) substrates remain largely unexplored. Here, we stabilize a metastable, unreconstructed Ir(110)-$(1\times 1)$ surface on which Fe forms a stable pseudomorphic double layer. Combining spin-polarized scanning tunneling microscopy and ab initio calculations, we reveal a right-handed Néel-type spin spiral along the $\left[\overline{1}10\right]$ crystallographic direction with a period of 1.27 nm as the magnetic ground state. Our analysis reveals this spiral is of the Yoshimori type, i.e., driven by frustrated Heisenberg interactions, with the Dzyaloshinskii-Moriya interaction determining its cycloidal nature and handedness.

In transmission electron energy loss (EEL) spectroscopy, the cross section in two dimensions (2D) is quenched by kinematic effects once the momentum transfer becomes smaller than a critical value set by $q_z$, the momentum loss parallel to the beam. Our highly momentum ($\mathrm{\Delta }q=0.02{\text{Å}}^{-1}$) and energy ($\mathrm{\Delta }E=45$ meV) resolved setup is instrumental in delivering the experimental verification of quenched 2D EEL spectra on freestanding graphene at momentum transfers $q$ below $0.06{\text{Å}}^{-1}$. We retrieve the intrinsic uniform dielectric response of graphene from measured spectra by quantifying the kinematic suppression.

We use ab initio calculations to evaluate the current-induced optical response and orbital moment accumulation at the surfaces of metallic films. These two quantities are related by a sum rule that equates the circular dichroic absorption integrated over frequency to the gauge-invariant self-rotation contribution to the orbital magnetization, ${\vec{M}}_{\mathrm{SR}}$. In typical ferromagnets, ${\vec{M}}_{\mathrm{SR}}$ is a good approximation to the total orbital magnetization. We compute the current-induced ${\vec{M}}_{\mathrm{SR}}$ for a Pt thin film and compare it to the current-induced orbital moment accumulation calculated with the atom-centered approximation (ACA). We find significant differences: the size of ${\vec{M}}_{\mathrm{SR}}$ is, in general, larger than the ACA orbital moment accumulation by an order of magnitude and includes substantial finite-size effects. The differences between the two quantities caution against interpreting optical measurements with models utilizing the ACA. Finally, we compute the total surface ${\vec{M}}_{\mathrm{SR}}$ and ACA orbital moment accumulation as a function of layer thickness. For both quantities, the length scale at which the total surface accumulation saturates is on the order of the mean free path and longer than the length scale of their spatial profiles.

In correlated quantum materials, divergent critical fluctuations near the quantum critical point are often closely associated with exotic quantum phases of matter, such as unconventional superconductivity and quantum spin liquids. Here we present a simple yet highly sensitive composite magnetoelectric (ME) method for detecting the critical spin fluctuations in quantum magnets. The ME signal is proportional to the magnetostriction coefficient, which directly probes the product of magnetization and spin-spin correlation. As a demonstration, the composite ME method is applied to a Kitaev quantum spin liquid candidate ${\mathrm{Na}}_3{\mathrm{Co}}_2{\mathrm{SbO}}_6$, which shows signs of magnetic field-induced quantum criticality. Notably, the ME signal prominently diverges at the magnetic field-induced tricritical points, particularly at a tricritical point that lies in close proximity to a zero-temperature quantum critical point. A crucial aspect of these tricritical points is their tunability through the modification of the in-plane magnetic field's direction. The direction of magnetic field can thus serve as a handy yet important tuning parameter, alongside pressure and chemical doping, for searching quantum critical points in quantum magnets with pronounced magnetic anisotropy.

We analyze a model for electronic structure and interactions in twisted transition metal chalcogenide ${\mathrm{WSe}}_2$ for superconductivity. In this material, spin-orbit scattering locks the $z$ components of spins of low-energy fermions near the $\mathbf{K}$ and ${\mathbf{K}}^{\prime }$ corner points of the hexagonal Brillouin zone, reducing the symmetry of spin-spin interactions to that of an XY model. We show that a nominally repulsive 4-fermion interaction gives rise to an attraction for pairing in a two-component $E^{-}$ channel, which is a hexagonal lattice representation of $\ell =1$ channels. The gap function is inversion-odd and a linear combination of spin singlet and spin triplet. At weak coupling, superconductivity emerges via the Kohn-Luttinger mechanism; we compute $T_c$ for the Fermi-level lying close to the van Hove singularity. At strong coupling, the pairing is mediated by XY magnetic fluctuations peaked at momenta $\mathbf{K}-{\mathbf{K}}^{\prime }=2\mathbf{K}$ and we estimate $T_c$ using the form of the quantum-critical XY fluctuations, displaying $\omega /T$ scaling.

We investigate the influence of hydrogen on the electronic structure of a binary transition metallic glass of ${\mathrm{V}}_{80}{\mathrm{Zr}}_{20}$. We examine the hybridization between the hydrogen and metal atoms with the aid of hard x-ray photoelectron spectroscopy. Combined with ab initio density functional theory, we are able to show and predict the formation of $s\text{−}d$ hybridized energy states. With optical transmission and resistivity measurements, we investigate the emergent electronic properties formed out of those altered energy states, and together with the theoretical calculations of the frequency-dependent conductivity tensor, we qualitatively support the observed strong wavelength-dependency of the hydrogen-induced changes on the optical absorption and a positive parabolic change in resistivity with hydrogen concentration.

The parallel-field Hall effect is the appearance of a Hall voltage $V_{\mathrm{H}}$ that is transverse to the current $I$ when a magnetic field $B$ is applied parallel to $I$ (i.e., $B\parallel I\perp V_{\mathrm{H}}$). Such an effect is symmetry forbidden in most cases and hence is very unusual. Interestingly, the existence of a finite parallel-field Hall effect was reported for the layered topological semimetal ${\mathrm{ZrTe}}_5$ and was proposed to be due to Berry curvature. However, it is forbidden for the known symmetry of ${\mathrm{ZrTe}}_5$ and the possible existence of a misaligned out-of-plane magnetic field was not completely ruled out. Here, we elucidate the existence of the parallel-field Hall effect in ${\mathrm{ZrTe}}_5$ with careful magnetic-field alignment. We interpret this result to originate from symmetry breaking and show that a tilting of the Fermi surface allowed by broken symmetry can explain the observed signal. This work demonstrates that the parallel-field Hall effect can be a powerful tool to detect tiny symmetry breaking that is otherwise difficult to detect.

We investigate a mechanism to produce superconductivity by strong purely repulsive interactions for flat dispersion $\varepsilon \sim k^4$ without using the pairing instability in a Fermi liquid. The resulting superconductors break both time-reversal and reflection symmetries in the orbital motion of electrons, and they exhibit nontrivial topological order. Our findings suggest that this topological chiral superconductivity is more likely to emerge near or between a fully spin-valley polarized metallic phase and a Wigner crystal phase. These topological chiral superconductors can be fully or partially spin-valley polarized. For partial spin-valley polarization, the ratios of electron densities associated with different spin-valley quantum numbers are quantized as simple rational numbers. Furthermore, many of these topological chiral superconductors exhibit charge-4 or higher condensation, neutral quasiparticles with fractional statistics, and/or gapless chiral edge states. Two of the topological chiral superconductors are in the same phases as the “spin”-triplet or spinless $p+ip$ BCS superconductor, while others are in different phases than from any BCS superconductors. The same mechanism is also used to produce anyon superconductivity between fractional anomalous quantum Hall states in the presence of a periodic potential.