The magnetization of amorphous sputtered films of a-$R_x\mathrm{C}{\mathrm{o}}_{1-x}$, with $x\approx 0.25$ and $R$ = Dy, Tb, or Tm, is investigated by magnetometry, anomalous Hall effect, and magneto-optic Kerr effect to understand how the magnetic structure of the films is influenced by temperature and the quadrupole and higher multipole moments of the rare-earth charge distribution. Square magnetic hysteresis loops with perpendicular magnetic anisotropy and divergent coercivity that reaches 3.5 T in the vicinity of the compensation temperature $T_{\mathrm{comp}}$ are observed at 175 and 200 K for Dy and Tb films, respectively, but the coercivity in Tm films never exceeds 0.5 T and shows no divergence near the compensation at 50 K. The temperature dependence of the net rare-earth moment is inferred from the cobalt moment of soft ferromagnetic a-${\mathrm{Y}}_x\mathrm{C}{\mathrm{o}}_{1-x}$. The magnitude of the second-order random anisotropy energy exceeds the antiparallel $R$-Co exchange coupling for all three rare earths. The negative quadrupole moments of Dy and Tb lead to random easy-axis anisotropy with large coercivity. The positive quadrupole moment of Tm favors random hard-axis anisotropy where each Tm has an easy plane. The resulting sperimagnetic ground states are modeled by a distribution of rare-earth moments within a cone of half-angle ${\theta }_0$ whose axis is antiparallel to the ferromagnetic axis of cobalt. The reduced moment $\langle J_z\rangle /J$ at $T$ = 0 is calculated from a one-atom Hamiltonian as a function of α, the ratio of uniaxial anisotropy to exchange energy per rare-earth atom for different angles θ between the local anisotropy axis, and the ferromagnetic Co axis. Extrapolated values of $\langle J_z\rangle /J$ are ∼0.75 at low temperature for both Dy and Tb, with a sharp increase <10 K attributed to higher-order multipole moments. The hard-axis random anisotropy resulting from the positive quadrupole moment of Tm leads to a larger low-temperature value of $\langle J_z\rangle /J$ = 0.84. On increasing temperature, the magnitude of the rare-earth moment and the local random anisotropy that creates the sperimagnetism are reduced; the cone angle narrows, but the noncollinear structure persists well above room temperature for Dy but not for Tb, a difference related to the opposite signs of their hexadecapole moments. A temperature-dependent spin-flop field observed near compensation in a-$\mathrm{D}{\mathrm{y}}_{25}\mathrm{C}{\mathrm{o}}_{75}$ extrapolates to 2.0 T at $T_{\mathrm{comp}}$, a remarkably low value that is associated with the nonrigid character and high transverse susceptibility of the frustrated Dy subnetwork. An x-ray photoemission electron microscopy investigation of partial single-pulse all-optical switching in a 10 nm a-$\mathrm{D}{\mathrm{y}}_{25}\mathrm{C}{\mathrm{o}}_{75}$ film as a function of temperature establishes that the process is stochastic, and unrelated to inhomogeneities in the films. The size of the sperimagnetic domains in the unmagnetized state is ∼200 nm, <300 K.

The van der Waals pseudobinary chalcogenides ${\left(ACh\right)}_m{\left(P{n}_{2}C{h}_3\right)}_n$ ($A=\mathrm{Ge},\mathrm{Mn},\mathrm{Pb},\mathrm{etc}.$; $Pn=\mathrm{Sb}\mathrm{or}\mathrm{Bi}$; $Ch=\mathrm{Te},\mathrm{Se}$) have recently been reported to host a vast landscape of topological phases of matter, including the quantum anomalous Hall state and topological axion state with a quantized magnetoelectric effect. A subgroup in this series, such as ${\mathrm{MnSb}}_4{\mathrm{Te}}_7$ and ${\mathrm{GeSb}}_4{\mathrm{Te}}_7$, can be driven to a superconducting state by applying physical pressure, making them viable candidates to realize so-called topological superconductivity. However, the role of magnetic fluctuations in this pressure-induced superconductivity remains unclear. Here, we report pressure-induced superconductivity in nonmagnetic ${\mathrm{GeBi}}_4{\mathrm{Te}}_7$, accompanied by the possible structural transitions evidenced from high-pressure Hall effect measurements, Raman scattering, and first-principles calculations. In comparison with other members in this family, we find the superconducting transition temperature of the nonmagnetic subgroup is significantly higher than their magnetic homologs, possibly hinting at the adversary role played by the magnetic fluctuations in the formation of superconductivity, at least in this pseudobinary chalcogenide family.

Superconductivity in the recently discovered altermagnetic materials hosts large prospects for both fundamental physics and technological applications. In this work, we show that a characteristic spin-sublattice locking in altermagnets puts severe constraints on possible superconducting pairing. In particular, by considering the archetypical two-band model for a $d_{x^2-y^2}$-wave altermagnet on a square lattice, we uncover that the most common form of superconductivity, uniform $s$-wave spin-singlet pairing is not possible to achieve in altermagnets. Instead, we find that the most likely forms of spin-singlet pairing have $d_{x^2-y^2}$- or extended $s$-wave symmetry. We also find that the simplest form of equal-spin-triplet $p$-wave pairing is not allowed, but only a mixed-spin-triplet $p$-wave state can exist. We verify these constraints on the superconducting pairing also within an interaction-induced model of altermagnetism, where we further establish their validity for finite-momentum pairing. Additionally we discuss the possible pairing symmetries for odd-frequency superconducting pairing. Due to the generality of our results, they are applicable to both intrinsic superconductivity and proximity-induced superconductivity in altermagnet-superconductor hybrid junctions.

The perovskite $\mathrm{BaSn}{\mathrm{O}}_3$ has an Sn $s$-orbital conduction band minimum, which makes it of interest as a transparent-conducting oxide parent compound but also contraindicates the ferroelectric instability characteristic of the related compound $\mathrm{BaTi}{\mathrm{O}}_3$. In this work, we studied the effect of (001) compressive strain on $\mathrm{BaSn}{\mathrm{O}}_3$ using first-principles methods. We found that, with low compressive strain, symmetry breaking takes cubic $\mathrm{BaSn}{\mathrm{O}}_3$ to a nonpolar tetragonal state, with a first-order phase transition to a hidden highly polarized ferroelectric supertetragonal state at ∼−5%. Based on the facts that the mismatch of the lattice constant in experiment between $\mathrm{BaSn}{\mathrm{O}}_3$ and $\mathrm{SrTi}{\mathrm{O}}_3$ is ∼−5.2% and coherent growth of $\mathrm{BaSn}{\mathrm{O}}_3$ on $\mathrm{SrTi}{\mathrm{O}}_3$ has been experimentally realized for $\mathrm{BaSn}{\mathrm{O}}_3$ layers thinner than 3 unit cells, we studied a series of $\mathrm{SrTi}{\mathrm{O}}_3/\mathrm{BaSn}{\mathrm{O}}_3$ superlattices with 1 or 2 unit cells of $\mathrm{BaSn}{\mathrm{O}}_3$ and several unit cells of $\mathrm{SrTi}{\mathrm{O}}_3$. We found that the superlattices are ferroelectric with large polarizations. We propose that the origin of ferroelectricity in the superlattices is the mechanical and electrical coupling of the $\mathrm{BaSn}{\mathrm{O}}_3$ and $\mathrm{SrTi}{\mathrm{O}}_3$ layers, with the polarized supertetragonal state of $\mathrm{BaSn}{\mathrm{O}}_3$ induced by compressive strain from the $\mathrm{SrTi}{\mathrm{O}}_3$ layers and polarization of the $\mathrm{SrTi}{\mathrm{O}}_3$ layers by the polar $\mathrm{BaSn}{\mathrm{O}}_3$ layers. Due to the distinctive electronic states in the $\mathrm{BaSn}{\mathrm{O}}_3$ layers, the realization of ferroelectricity holds promise for the design of electronic devices.

We investigate the pressure-driven structural and electronic evolution of ${\mathrm{PdSe}}_2$ using powder x-ray diffraction, Raman spectroscopy, and first-principles calculations. Beyond 2.3 GPa, suppression of the Jahn-Teller distortion induces in-plane lattice expansion and metallization. Around 4.8 GPa, the interlayer $d_{z^2}-{\pi }^{*}$ orbital hybridization drives the dimensional crossover, facilitating the transformation from the two-dimensional distorted to a three-dimensional undistorted pyrite phase. At $\sim 9\mathrm{GPa}$, a novel phase emerges, characterized by octahedral distortions in the $d$ orbitals of Pd. Structural analysis suggests the presence of marcasite ($Pnnm$) or arsenopyrite ($P{2}_1/c$) phase with orthorhombic and monoclinic configurations, respectively. Furthermore, the observed phonon anomaly and electronic structure modifications, including the emergence of flat bands in the high-pressure phases, elucidate the fundamental mechanisms underlying the previously reported exotic superconductivity with an enhanced critical temperature. These results highlight the pivotal role of dimensional crossover and structural transitions in tuning the electronic properties of puckered materials, providing pathways for novel functionalities.

Tin (Sn), a well-known element intensively studied for its multiple structural transformations under pressure, exhibits unclear high-pressure melting behavior with limited dynamic experimental data. This study combines shock compression experiments using lithium fluoride (LiF) and magnesium oxide (MgO) transparent windows with ab initio molecular dynamics (AIMD) simulations to determine the melting curve of Sn up to 61 GPa. The shock melting data of Sn from 34 to 44 GPa were determined using LiF window and extended to 61 GPa using MgO window, leveraging MgO's impedance matching with Sn to probe near-Hugoniot release states. Dynamic emissivity and radiance were measured simultaneously at the Sn/window interface using a multichannel pyrometry system, enabling accurate temperature determination under shock release conditions. A consistent melting curve was determined by the dynamic experiments and AIMD calculations using Z method, in agreement with the results of other dynamic measurements in the pressure range of 10–39 GPa. The results reconcile the recently reported static measurements and theoretical discrepancies, and provide a reliable melt boundary for establishing a physical model of Sn at extremes. Our direct shock measurements with simultaneous emissivity-radiance diagnostics and atomic-scale simulations have implications for resolving high-pressure melting behavior of other multivalent metals.

Cs-based semiconductors like ${\mathrm{Cs}}_3\mathrm{Sb}$ and ${\mathrm{Cs}}_2\mathrm{Te}$ are currently used as photocathodes in particle accelerators. Their performance as electron sources critically depends on their interaction with intense laser sources. However, detailed studies on their strong-field excitation dynamics are currently missing. In this work, we employ real-time time-dependent density functional theory to investigate from first principles the time-dependent response of ${\mathrm{Cs}}_3\mathrm{Sb}$ and ${\mathrm{Cs}}_2\mathrm{Te}$ to ultrafast pulses of varying intensities, ranging from $1\mathrm{GW}/{\mathrm{cm}}^2$ to $1\mathrm{PW}/{\mathrm{cm}}^2$. Our analysis reveals that nonlinear effects, including high-harmonic generation, emerge with intensities of $100\mathrm{GW}/{\mathrm{cm}}^2$ in ${\mathrm{Cs}}_3\mathrm{Sb}$ and $200\mathrm{GW}/{\mathrm{cm}}^2$ in ${\mathrm{Cs}}_2\mathrm{Te}$. We show that beyond these thresholds, the excitation mechanisms evolve from one-photon absorption saturation to increasingly dominant multiphoton absorption (above $1\mathrm{TW}/{\mathrm{cm}}^2$ for ${\mathrm{Cs}}_3\mathrm{Sb}$ and $5\mathrm{TW}/{\mathrm{cm}}^2$ for ${\mathrm{Cs}}_2\mathrm{Te}$). Under the highest field intensities ($>10\mathrm{TW}/{\mathrm{cm}}^2$), the onset of tunnel ionization is identified through occupation analysis. These findings offer material-specific insights into the nonlinear optical properties and nonequilibrium electron distributions in the femtosecond regime of these photocathode materials, providing valuable indications to optimize their performance and stability as high-brightness electron sources.

Nematicity plays an important role in strongly correlated electron systems. We explore the spin nematicity of a spin-1 kagome lattice antiferromagnet with the bilinear-biquadratic model and single-ion anisotropy using a generalized semiclassical approximation and Monte Carlo simulations. We reveal a rich ground state phase diagram, characterized by two main regions: a pure spin nematic phase and a region featuring the coexistence of a classical spin liquid and ferroicities for both dipolar and quadrupolar moments. The thermal fluctuation melts the spin nematic order into a critical phase with a quasi-long-range nematic order. Due to the fluctuating vortices of the spin nematic order, this critical phase further undergoes a nematic Berezinskii-Kosterlitz-Thouless transition to a paramagnetic phase, marked by an anomalous stiffness jump. Additionally, the single-ion anisotropy leads to weak ferromagnetism, resulting in spontaneous time-reversal symmetry breaking at very low temperatures. Remarkably, both two types of ferroic ordering are accompanied by classical spin liquid behaviors. Our results provide an intriguing glimpse into the interplay between geometric frustration and intertwining spin orders with different ranks and are expected to stimulate further studies on spin-1 systems and relevant materials.

We show that a quadratic form of the quantum geometric tensor in $k$ space sets a bound on the $q^4$ term in the static structure factor $S\left(q\right)$ at small $\mathit{q}$. Bands that saturate this bound satisfy a condition similar to Laplace's equation, leading us to refer to them as harmonic bands. We provide examples of harmonic bands in one- and two-dimensional systems, including (higher) Landau levels. The geometric bound further leads to a topological bound on the $q^4$ term, which is saturated only when the band geometry satisfies the trace condition and, additionally, the quantum geometric tensor is uniform in $k$ space. We speculate that these bounds taken together provide a useful guide for identifying Chern bands that favor (Abelian or non-Abelian) fractional Chern insulators.

Nonlinear helicity-dependent photocurrents have been reported in three-dimensional topological materials lacking inversion symmetry. Here, we theoretically study the charge and spin photocurrents generated by linear and circularly polarized radiation in ultrathin topological insulator films. Using time-dependent perturbation theory and detailed balance equations, we find that helical transverse spin currents are generated when the symmetry between the top and bottom film surfaces is disturbed. Such spin currents are invariant under in-plane mirror transformations but have $s$-wave and $d$-wave components in regard to transformations under $\pi /2$ rotations. Spin-current phototransistors and amplifiers can be based on these effects.

The imbalanced Hubbard model features a transition between dynamic regimes depending on the mass ratio and coupling strength between two different particle species. A slowdown of the lighter particle transport can be attributed to an emergent effective disorder induced by the heavy particles for high mass ratio and strong coupling. This subdiffusive regime has been interpreted as a Griffiths phase, linking the effect to the coexistence of metallic and insulating regions. Here, we investigate the dynamics of the heavy particles, which also reveals subdiffusive behavior, yet cannot be explained within the Griffiths picture. We demonstrate that heavy particles predominantly form small clusters, mainly pairs, during the dynamical process, which reduces their propagation speed and transiently shifts the time-dependent diffusion constant into the subdiffusive regime at late times. The necessary attraction between particles driving this process can be understood within the Born-Oppenheimer approximation. We introduce a classical one-dimensional random walk model that can quantitatively reproduce the subdiffusion dynamics in the strong coupling regime.

We investigate the impact of quantum noise on non-Hermitian resonators at an exceptional point. The system's irreversible Markovian dynamics is modeled using the Lindblad master equation, which accounts for the incoherent pump, radiative losses, and external monochromatic field. An exact analytic solution is derived in the form of the characteristic function of the Husimi distribution, enabling the calculation of all quantum mechanical observables associated with the bosonic degrees of freedom. Our analysis reveals that quantum noise strongly influences the system's response when the system exhibits $\mathcal{P}\mathcal{T}$ symmetry. Out of the $\mathcal{P}\mathcal{T}$-symmetric regime, however, the system demonstrates stability within a specific parametric domain, where the effects of quantum noise on the signal-to-noise ratio can be mitigated by increasing the external field.

The contribution of flexoelectric coupling to the long-range order parameter fluctuations in ferroics can be critically important to the ferron dispersion and related polar, pyroelectric, and electrocaloric (EC) properties. Here, we calculate analytically the dispersion relations of soft optic and acoustic flexocoupling-induced phonons and ferrons by incorporating the flexoelectric coupling, damping, and higher elastic gradients in the Landau-Ginzburg-Devonshire free-energy functional using the van der Waals uniaxial ferrielectric $\mathrm{CuIn}{\mathrm{P}}_2{\mathrm{S}}_6$ as an example. We analyze the changes in the flexocoupling-induced phonon and ferron spectra arising from the appearance of spatially modulated phases induced by the flexoelectric coupling. We show that the free-energy landscape of $\mathrm{CuIn}{\mathrm{P}}_2{\mathrm{S}}_6$ determines the specific features of its phonon spectra and ferron dispersion. We also discuss the contributions of optic and acoustic flexocoupling-induced ferrons to the pyroelectric and EC responses of $\mathrm{CuIn}{\mathrm{P}}_2{\mathrm{S}}_6$ at low temperatures.

Recently, the discovery of topological photonic alloys with a local breakdown of time-reversal symmetry (TRS) has significantly broadened our understanding of conventional photonic Chern insulators with global TRS breaking and robust chiral edge states (CESs). However, to date, topological photonic alloys have been limited to periodic or quasiperiodic lattices, which have both long-range and short-range orders. It is still an open question whether the concept of topological photonic alloy can be extended to amorphous lattices that lack long-range order but only have short-range order. In this article, by mixing magnetized and nonmagnetized gyromagnetic rods in disordered lattices, we theoretically demonstrate that amorphous topological photonic alloys can support nontrivial Chern band gaps and robust CESs. Moreover, by increasing the disorder strength in amorphous lattices, we find that the threshold concentration of magnetized gyromagnetic rods to open the Chern band gaps also increases. Beyond a critical disorder strength, the signatures of Chern band gaps and CESs thoroughly disappear, even with pure magnetized gyromagnetic rods. Our work broadens the research scope of topological photonic alloys and may have potential applications in nonreciprocal topological photonic devices.

The non-Hermitian skin effect is the accumulation of eigenstates at the boundaries, reflecting the system's nonreciprocity. Introducing disorder leads to a competition between the skin effect and Anderson localization, giving rise to the skin-Anderson transition. Here, we investigate wave packet spreading in the disordered Hatano-Nelson model and uncover distinct dynamical behaviors across different regimes. In the clean limit, transport is unidirectionally ballistic ($\mathrm{\Delta }x\sim t$) due to nonreciprocity. For weak disorder, where skin and Anderson-localized modes coexist, transport transitions from ballistic at early times to superdiffusive ($\mathrm{\Delta }x\sim t^{2/3}$) at long times. In the deeply Anderson-localized regime, initial diffusion ($\mathrm{\Delta }x\sim t^{1/2}$) eventually gives way to superdiffusive spreading. We examine how these scaling behaviors emerge from the system's spectral properties and eigenstate localization behaviors. Our work unveils the rich dynamics driven by nonreciprocity and disorder in non-Hermitian systems.

We study conventional and out-of-time-ordered correlators (OTOCs) for a wide variety of transverse field Ising chains: classical and quantum, clean and disordered, and integrable and generic. The setting we consider is that of a quantum quench. We find a remarkably rich phenomenology, ranging from stable periodic signals to ones decaying with varying rates. This variety is due to a complex interplay of constraints on thermalization imposed by integrability and symmetry. A process we term dynamical domain wall relocalization provides a long-lived signal in the clean, integrable case, which can be degraded by the addition of disorder even without interactions. Our results shed light on a proposal to use an OTOC as a dynamical diagnostic of a quantum phase more powerful than a standard observable.

The nature of domain wall (DW) dynamics in synthetic ferrimagnetic multilayers composed of $\mathrm{Pt}\left|\mathrm{Co}\right|\mathrm{Tb}|\mathrm{Al}$ for different Tb thickness has been explored, focusing on the underlying pinning parameters, and on the different regimes of DW dynamics driven by spin-orbit torques (SOTs). We find that because of the AFM coupling between Co and Tb, the magnetic moment of Tb increases with Tb thickness resulting in a reduced saturation magnetization and an enhanced depinning field. The DW disorder interaction is found to vary weakly with the AFM coupling between Co and Tb, while the complete withdrawal of the Tb layer strongly increases the anisotropy and the DW pinning. Furthermore, we propose an approach to measure effective SOTs by comparing depinning transitions in current- and field-induced DW motion. This research reveals insights into DW dynamics in coupled AFM systems, highlighting enhancements in mobility through optimized SOTs and pinning landscapes.

We report the magnetic ground state, spin excitations, and spin Hamiltonian of the two-dimensional (2D) spin-1 trimerized Heisenberg antiferromagnet (AFM) $\mathrm{L}{\mathrm{i}}_2\mathrm{N}{\mathrm{i}}_3{\mathrm{P}}_4{\mathrm{O}}_{14}$. Below the magnetic ordering temperature $T_{\mathrm{N}}=14.5$ K, the compound exhibits a canted long-range antiferromagnetic order with a propagation vector $k$  = (0 0 0), consistent with the magnetic space group $P{2}_1/c.1$ (No. 14.75). The ground-state magnetic structure consists of ferromagnetic (FM) spin trimers of $\mathrm{N}{\mathrm{i}}^{2+}$ ions. The spin trimers are coupled antiferromagnetically along the $c$ axis and ferromagnetically along the $a$ axis. Inelastic neutron scattering (INS) reveals gapped and dispersive magnon excitations below the $T_{\mathrm{N}}$, and gapless quasielastic scatterings at higher temperature. The linear spin-wave theory simulations reveal the essential features of the excitation spectrum by a spin Hamiltonian composed of ferromagnetic intratrimer exchange interaction $J_1$ and intertrimer exchange interactions $J_2$ (FM) and $J_3$(AFM) within the $bc$ plane. The $J_2$ and $J_3$ are along the $b$ axis and $c$ axis, respectively, with strengths of $J_2/J_1=0.79$ and $J_3/J_1\sim =-0.91$. In addition, a weak interplanar ferromagnetic exchange interaction $J_4 \left(\right|J_4/J_1|\sim 0.12$ is found along the $a$ axis. The determined exchange constants reveal a 2D trimerized collinear-II spin lattice within the $bc$ plane. The analysis of INS spectra by linear spin-wave theory also yields a moderate single-ion anisotropy ($D/J_1=0.48$), which accounts for the observed spin gap below $T_{\mathrm{N}}$ as well as the metamagnetic transition near 44 kOe in dc magnetization ($M$ vs $H$) curves. These findings identify $\mathrm{L}{\mathrm{i}}_2\mathrm{N}{\mathrm{i}}_3{\mathrm{P}}_4{\mathrm{O}}_{14}$ as a rare realization of a two-dimensional trimerized spin system and offer the direct experimental confirmation of theoretically predicted magnon excitations, unveiling the fundamental characteristics of the expected excitation spectrum.