The spin collinear altermagnet (AM) material ${\mathrm{RuO}}_2$ was shown to exhibit a time-odd transverse spin current driven by a longitudinal electric field [González-Hernández et al., Phys. Rev. Lett. 126, 127701 (2021)]. In this work we demonstrate theoretically that there exists a time-even transverse charge current besides the spin current in the same AM material without involving any spin-orbit interaction, which is crucially dependent on the angle between the crystalline axis and the applied electric field. The origin is the nonrelativistic alternating spin-momentum coupling as well as the spin-dependent anisotropic group velocity of electrons. The transverse charge current is weaker than the spin counterpart but can be enhanced by introducing time-symmetry-broken ingredients such as external magnetization.

We propose a framework to construct a real-space spin model based on the inverse Hamiltonian design. The method provides an efficient way of realizing unconventional topological spin textures by optimizing the interaction parameters. In order to demonstrate its usefulness, we show that the tuning of the long-range exchange interactions can give rise to a square skyrmion crystal even without factors that have been previously identified as prerequisites for its stabilization, such as a Dzyaloshinskii-Moriya interaction, a multispin interaction, and bond-dependent magnetic anisotropy. Moreover, we elucidate the essence for the emergence of the square skyrmion crystal by classifying the parameter sets we obtain by the method. Since the present framework by adopting machine learning techniques can be universally applied to any magnetic system irrespective of lattice structures, it serves as the efficient construction of an effective spin model and the understanding of the stabilization mechanisms for unconventional topological spin orders.

Magnetic domains and other forms of quasistatic spontaneous disorder drive nonergodic behaviors that can lead to unusual material properties. We examine these behaviors near a spin spiral stripe melting transition in an amorphous FeGe thin film using coherent resonant soft x-ray scattering. We find that the system is ergodic very close to the transition, as reflected by a nearly Gaussian distribution of fluctuations. At slightly lower temperature the distribution is skewed, implying nonergodicity. The distributions can be resolved into two distinct components reflecting two different kinds of fluctuating spin structures, one at a shorter and one at a longer length scale. Our results delineate an approach to evaluate the statistics of fluctuations in many classes of nanoscale heterogeneous materials.

Two-dimensional (2D) carrier systems exhibit various significant physical phenomena for electronics and spintronics, where one of the most promising traits is efficient spin-to-charge conversion stemming from their Rashba-type spin-orbit interaction. Meanwhile, a nuisance in quests of promising materials for spintronics application is that the vast majority of the investigated platforms consist of rare and/or toxic elements, such as Pt and Te, which hinders progress of spin conversion physics in view of element strategy and green technology. Here, we show the emergence of giant spin-orbit torque driven by two-dimensional hole gas at the surface of hydrogen-terminated diamond, where the constituent substances are ubiquitous elements, carbon and hydrogen. The index of its spin torque efficiency at room temperature is several times greater than that of rare metal Pt, the benchmark system/element for spin-to-charge conversion. Our finding opens a pathway for more sustainable spintronics and spin-orbitronics applications, with efficient spin-orbit torque employing ubiquitous nontoxic elements.

Motivated by the recent experimental demonstration of the doping dependence of the linear-in-temperature resistivity coefficient in cuprates, we numerically investigated the three-orbital Emery model focusing on the slope of the $T$-linear electronic and quasiparticle scattering rates by adopting dynamical cluster quantum Monte Carlo simulations. Our exploration discovered that the slope of electronic scattering rate evolves linearly with the electron doping; while it is inversely proportional to the hole-doping level at the intermediate doping regime and then crossovers to the linearlike dependence on further hole doping. These features remarkably match with the experimental findings qualitatively. We further discuss the doping-dependent slope of the quasiparticle scattering rate and also estimate the resistivity coefficient. Our presented work provides promising insight on the three-orbital Emery model, particularly its doping evolution and connection to the underlying mechanism of the $T$-linear resistivity in cuprates.

Flat bands, where Coulomb repulsion dwarfs bandwidth, hold the potential to realize many correlated electron states in a material. Rhombohedral graphite (RG) hosts an intrinsic flat band near the Fermi level localized on its top and bottom surfaces, in which the density of states is predicted to increase sharply with increasing crystal thickness. Here, we study rhombohedral graphite samples of multiple thicknesses using scanning tunneling microscopy and spectroscopy. We observe a van Hove singularity (vHs) in the density of states of all samples as well as additional peaks corresponding to the onsets of higher-energy bands that have been pushed away from the Fermi level due to interlayer hopping. The relative height of the central vHs to the higher-energy peaks increases with crystal thickness, a result that agrees quantitatively with our tight-binding (TB) calculations. We study the boundary between RG and hexagonal graphite and observe splitting of the flat surface band, an effect which can be described by the inclusion of a stacking fault into our TB model.

It was recently reported that molten sulfur exhibits a first-order liquid-liquid transition (LLT) with a critical point. The phase diagrams of selenium (Se) and sulfur are very similar, and experiments have suggested that LLT may also happen in molten Se. Here, complete ab initio molecular dynamics simulations (AIMD) and a combination of AIMD and machine learning are used to study the pressure-induced structural change of molten Se. Here the simulation density range is expanded, the number of atoms and simulation time are significantly increased, and the van der Waals correction (VDW) is considered. According to our findings, the liquid structure undergoes two changes along the 1000 K isotherm. Nevertheless, neither change is first order. The significance of the VDW interaction is demonstrated by the perfect agreement of the transition pressure with the experiments after considering the VDW correction. We contend that the increase in conductivity seen in the experiments is connected to the first structural change, which results from the effect of temperature on the weakly Peierls distorted structures. The maximum of the melting curve of crystalline Se-I is associated with the second structural change, which is the pressure-induced Peierls transition.

We present comprehensive high magnetic field studies of the alternating weakly coupled ferro-antiferromagnetic (FM-AFM) spin-$1/2$ chain compound ${\mathrm{Cu}}_2$(${\mathrm{OH})}_3\mathrm{Br}$, with the structure of the natural mineral botallackite. Our measurements reveal a broad magnetization plateau at about half of the saturation value, strongly suggesting that the FM chain sublattice becomes fully polarized, while the AFM chain sublattice remains barely magnetized, in magnetic fields at least up to 50 T. We confirm a spin-reorientation transition for magnetic fields applied in the $a{c}^{*}$ plane, whose angular dependence is described in the framework of the mean-field theory. Employing high-field THz spectroscopy, we reveal a complex pattern of high-frequency spinon-magnon bound-state excitations. On the other hand, at lower frequencies we observe two modes of antiferromagnetic resonance, as a consequence of the long-range magnetic ordering. We demonstrate that applied magnetic field tends to suppress the long-range magnetic ordering; the temperature-field phase diagram of the phase transition is obtained for magnetic fields up to 14 T for three principal directions ($a, b, c^{*}$).

The nuclear magnetic resonance (NMR) spectrum of spin-3/2 nuclei in a static magnetic field aligned with one of the electric field gradient (EFG) principal axes is developed analytically, based on fictitious spin-1/2 formalism. Compact closed-form expressions for the eigenstates and transitions frequencies, as well as the expectation value of the magnetic moment after resonant excitation, are derived. Emphasis is placed on defining and interpreting the associated Rabi frequencies, as a function of excitation direction and ellipticity. It is found that transitions inherently fall into two subsets, depending on their sensitivity to excitation direction, with the Rabi frequency of one subset directly depending on the asymmetry of the EFG. A natural application is the study of Fe-based superconductors, whose antiferromagnetic ordering at low temperatures leads to a strong intrinsic magnetic field aligned with the EFG principal axes. Zero external-field NMR spectra, from powder samples of two such Fe-based superconductors, ${\mathrm{BaFe}}_2{\mathrm{As}}_2$ and ${\mathrm{CaFe}}_2{\mathrm{As}}_2$, are analyzed and exemplify the simplicity in extracting the internal magnetic field, the quadrupole coupling constant, and the EFG asymmetry parameter, which are important for studying magnetic ordering, structural properties, phase transitions, and NMR dynamics. Results compare favorably to conventional high-field NMR experiments done with the rotation of single crystals. Overall, the physical insights, afforded by the exact and concise expressions, will lead to ready interpretation of spin-3/2 spectra as well as precipitating new experimental directions.

High-precision magnetometers have found wide applications in medicine, geological exploration, material property studies, and other fields of human activity. Recently, there has been significant development in magnetometers based on the evolution of quantum system states under the influence of an external magnetic field. A notable example of such a quantum system is the fluxonium superconducting qubit. In this paper, we evaluate the performance of a low-frequency magnetic field sensor based on the fluxonium qubit. The analysis utilizes parameters from qubits implemented by various experimental groups. We compare the performance of a fluxonium-based magnetometer with that of superconducting quantum interference devices. Our calculations show that fluxonium-based magnetometers are capable of high-precision measurements and that the high intrinsic inductance of the fluxonium loop allows efficient coupling with auxiliary antennas. Moreover, we propose the algorithm upgrade for low-frequency magnetic field measurements using qubits, which could enhance measurement accuracy by approximately a factor of two compared to existing qubit-based algorithms.

We investigate the anomalous thermal Hall effect (ATHE) in Weyl superconductors realized by the $E_{1u}$ ($p$ wave and $f$ wave) chiral superconducting order for the point group $D_{6h}$. Using the quasiclassical transport theory, we analyze the influence of the impurity scatterings and the line-nodal excitations on the ATHE. We compare the extrinsic (impurity-induced) ATHE with the intrinsic (topological) ATHE to identify the dominant contribution. Because the transverse response is sensitive to the slope in the density of states (DOS) at the Fermi energy, the extrinsic ATHE vanishes in both the Born (weak impurity potential) and unitarity (strong impurity potential) limits. The amplitude of the impurity contribution to the thermal Hall conductivity (THC) reaches maximum between these limits when the slope of the DOS becomes large due to impurity bands near the Fermi energy. In such situations, the extrinsic ATHE dominates the intrinsic ATHE even at low temperatures. The extrinsic ATHE is sensitive to line-nodal excitations, whereas the intrinsic ATHE is insensitive to bulk excitations. When line nodes involve the sign change of the order parameter, the impurity contribution to the THC is suppressed even though the phase space for low-energy excitation is large. In contrast, if line nodes are not accompanied by such sign changes, the extrinsic ATHE is significantly enhanced. Our results form a basis for the comprehensive analysis of anomalous thermal transport in Weyl superconductors.

The Kitaev chain model with a spatially modulated phase in the superconducting order parameter exhibits two types of topological transitions, namely, a band topology transition between trivial and topological gapped phases, and a Fermi surface Lifshitz transition from a gapped to a gapless superconducting state. We investigate the correlation functions of the model for arbitrary values of superconducting coupling ${\mathrm{\Delta }}_0$, chemical potential $\mu$, and phase modulation wavevector $Q$, characterizing the current flowing through the system. In the cases $\mu =0$ or $Q=\pm \pi /2$ the model turns out to exhibit special symmetries, which are proven to induce an even/odd effect in the correlations as a function of the distance $l$ between two lattice sites, as they are nonvanishing or strictly vanishing depending on the parity of $l$, measured in the lattice spacing unit. We identify a clear difference between the band topology and the Lifshitz transition through the $Q$ dependence of the short distance correlation functions, which, in particular, exhibit pronounced cusps with discontinuous derivatives across the Lifshitz transition. We also determine the long-distance behavior of correlations, finding that in the gapped phase there can be various types of exponential decays and that in the gapless phase the algebraic decay is characterized by two different spatial periods, depending on the model parameters. Furthermore, we establish a connection between the gapless superconducting phase of the Kitaev chain and the chiral phase of spin models with Dzyaloshinskii-Moriya interaction.

We perform first-principles simulations to construct a multiphase equation of state (EOS) for magnesium (Mg) up to a pressure-temperature $\left(P\text{−}T\right)$ range of 600 GPa and 8000 K. The phases considered include the solid hexagonal close-packed (hcp) and body-centered cubic (bcc) phases and the liquid phase. The effects of lattice anharmonicity on the free energies of the solid phases are considered using the phonon quasiparticle method, which is a hybrid approach that combines first-principles molecular dynamics (FPMD) and harmonic phonons to address lattice anharmonicity. These effects are found to significantly increase the calculated hcp-bcc transition pressure at high temperatures by >10% at $T>1000$ K and $>20\%$ at $T>1250$ K, leading to an hcp-bcc phase line in good overall agreement with static measurements. The free energies of the liquid phase are fitted using the results of FPMD simulations of this phase and constrained by our previous melting curve calculated from FPMD using the solid-liquid coexistence method. The resulting melting curve from our EOS reproduces the anomalous behavior of reentrant melting above ∼300 GPa from our previous calculations and shows better agreement with the results from shock experiments than with static measurements at high pressures. Our EOS places the hcp-bcc-liquid triple point at 25 GPa and 2030 K, higher in pressure and temperature than those from previous first-principles studies based on the quasiharmonic approximation (QHA). Comparisons are also made with other experimental data, including those from various static and shock experiments and generally indicate a high level of consistency.

Dynamical quantum phase transitions are nonanalyticities in a dynamical free energy (or return rate), which occur at critical times. Although extensively studied in one dimension, the exact nature of the nonanalyticity in two and three dimensions has not yet been fully investigated. In two dimensions, results so far are known only for relatively simple two-band models. Here, we study the general two- and three-dimensional cases. We establish the relation between the nonanalyticities in different dimensions, and the functional form of the densities of Fisher zeros. We show, in particular, that entering a critical region where the density of Fisher zeros is nonzero at the boundary always leads to a cusp in the derivative of the return rate while the return rate itself is smooth. We illustrate our results by obtaining analytical results for exemplary two- and three-dimensional models.

The magnetic ground state is crucial for applications of two-dimension magnets because it determines the fundamental magnetic properties of the material, such as magnetic order, magnetic transition temperature, and low-energy excitation of the spin waves. However, simulations of the magnetism of local-electron systems are challenging due to the existence of metastable states. In this study, occupation matrix control and density functional theory plus Hubbard's $U$ calculations are applied to investigate the magnetic ground state of monolayer ${\mathrm{CeI}}_2$. Following the predicted ferromagnetic (FM) order, the FM ground state and the FM metastable states are identified and found to have different values for the magnetic parameters. Based on the calculated magnetic parameters of the FM ground state, the Curie temperature is estimated to be 128 K for monolayer ${\mathrm{CeI}}_2$. When spin-orbit coupling (SOC) is considered, the FM ground state is further confirmed to contain both off-plane and in-plane components of magnetization. SOC is shown to be essential for reasonably describing not only magnetic anisotropy but also the local electronic orbital state of monolayer ${\mathrm{CeI}}_2$.

We investigate the critical properties of the Anisotropic Next-Nearest-Neighbor Ising (ANNNI) model using a feedback-based quantum algorithm (FQA). We demonstrate how this algorithm enables the computation of both ground and excited states without relying on classical optimization methods. By exploiting symmetries in the algorithm initialization, we show how targeted initial states can increase convergence and facilitate the study of excited states. Using this approach, we study the quantum phase transitions with the Finite Size Scaling method, analyze correlation functions through spin correlations in the ground state, and examine magnetic structure by calculating structure factors via the Discrete Fourier Transform. Our findings highlight FQAs potential as a versatile tool for studying not only the ANNNI model but also other quantum systems, providing insights into quantum phase transitions and the magnetic properties of complex spin models.

Developing two-dimensional valleytronic materials with spin-valley coupling attracts great interest in the field of valleytronics and spintronics devices. Here, starting from a tight-binding model based on a colorful triangle lattice, we suggest that the valley polarization can be realized in monolayer ${\mathrm{Ti}}_3{X}_3{Y}_2$ ($X$ = S, Se; $Y$ = S, Se, Te) by using first-principles calculations. Our results show that the proposed monolayer exhibits intrinsic ferrovalley with large valley polarization, derived from the time-reversal and $C_2$ symmetry broken, which is beneficial for observing the anomalous valley hall effect in these systems. Furthermore, strain engineering can induce the ferrovalley semiconductor to half-valley metal transition in monolayer ${\mathrm{Ti}}_3{X}_3{Y}_2$. Our work not only provides a platform for two-dimensional (2D) valleytronic research but also promises the fundamental research of coupling physics in 2D lattices.

Epitaxial ${\mathrm{CoV}}_2{\mathrm{O}}_4$ (CVO) thin films were fabricated on different substrates, and strain-induced magnetic anisotropy is observed in the films. The magnetic easy axis of CVO thin film under compressive strain changes from out-of-plane to in-plane $<83$ K, while under a small tensile strain, the spin direction orientates from in-plane to out-of-plane $<75$ K. It is found that, under compressive strain, above the reorientation temperature, Co-V exhibits strong antiferromagnetic interaction. Due to a significant out-of-plane anisotropy of ${\mathrm{V}}^{3+}$, the total spin of CVO tends to be out-of-plane oriented. Below the reorientation temperature, the V-V interaction is prominent, leading to an itinerancy of ${\mathrm{V}}^{3+} 3d$ electrons and thereby weakening the magnetocrystalline anisotropy of the sample. Dominated by the shape anisotropy, the total spin of CVO epitaxial film changes to the in-plane orientation. When CVO film is subjected to a small tensile strain, the magnetocrystalline anisotropy is relatively weak. The change in the easy magnetization direction cannot be explained by the single-ion anisotropy of ${\mathrm{Co}}^{2+}$ or ${\mathrm{V}}^{3+}$ and shape anisotropy but can be understood by the strain-induced anisotropy related to the magnetostriction coefficient.

The minority-spin Fe/MgO interface states are at the Fermi level in density functional theory (DFT), but experimental evidence and GW calculations place them slightly higher in energy. This small shift can strongly influence tunneling magnetoresistance (TMR) in junctions with a thin MgO barrier and its dependence on the concentration of Co in the electrodes. Here, an empirical potential correction to DFT is introduced to shift the interface states up to match the tunnel spectroscopy data. With this shift, TMR in Fe/MgO/Fe junctions exceeds 800% and 3000% at 3 and 4 monolayers (ML) of MgO, respectively. We further consider the effect of alloying of the Fe electrodes with up to 30% Co or 10% V, treating them in the coherent potential approximation (CPA). Alloying with Co broadens the interface states and brings a large incoherent minority-spin spectral weight to the Fermi level. Alloying with V brings the minority-spin resonant states close to the Fermi level. However, in both cases the minority-spin spectral weight at the Fermi level resides primarily at the periphery of the Brillouin zone, which is favorable for spin filtering. Using convolutions of ${\mathbf{k}}_{\parallel }$-resolved barrier densities of states calculated in CPA, it is found that TMR is strongly reduced by alloying with Co or V but still remains above 500% at 4 ML of MgO up to 30% of Co or 5% V. At 5 ML, the TMR increases above 1000% in all systems considered. However, while TMR declines sharply with increasing bias up to 0.2 eV in the tunnel junctions with pure Fe leads, it remains almost constant up to 0.5 eV if leads are alloyed with Co.

We theoretically investigate the supercurrent flow in a Josephson junction consisting of two spin-split superconductors combined by a normal metal weak link. The normal metal may be driven out of equilibrium, thus modifying the electron and hole occupation and consequently the supercurrent through the system. Considering first an equilibrium normal metal, we find that increasing the spin-splitting field can enhance the supercurrent strongly for long junctions at low temperatures. In contrast to previous work, this is a much larger enhancement (over 100%) and it is achieved for both parallel and antiparallel spin-splitting field configurations, making the effect robust. On the other hand, when a gate voltage is applied to drive the system out of equilibrium, we demonstrate a more efficient $\pi$ transition of the supercurrent in terms of a lower transition voltage by tuning the spin splitting. Moreover, we find the application of temperature bias strongly suppresses the supercurrent, resulting in very sharp supercurrent jumps as outputs.