We revisit spin-orbit coupling in a plasmonic Berry metasurface composed of rotated nanoapertures, which is known to imprint a robust far-field polarization response. We present a scattering formalism that shows how that spin-momentum locking emerges from the geometry of the unit cell without requiring global rotation symmetries. We find and confirm with Mueller polarimetry measurements that spin-momentum locking is an approximate symmetry. The symmetry breakdown is ascribed to the elliptical projection of circularly polarized light into the planar surface. This breakdown is maximal when surface waves are excited, and a new set of spin-momentum locking rules is presented for this case.

The interplay of topology and competing interactions can induce enriched phases and phase transitions at finite temperatures. We consider a weakly coupled two-dimensional hexatic-nematic XY model with a relative $Z_3$ Potts degrees of freedom, and apply the matrix product state method to solve this model rigorously. Since the partition function is expressed as a product of two-legged one-dimensional transfer matrix operator, an entanglement entropy of the eigenstate corresponding to the maximal eigenvalue of this transfer operator can be used as a stringent criterion to determine various phase transitions precisely. At low temperatures, the intercomponent $Z_3$ Potts long-range order (LRO) exists, indicating that the hexatic and nematic fields are locked together and their respective vortices exhibit quasi-LRO. In the hexatic regime, below the BKT transition of the hexatic vortices, the intercomponent $Z_3$ Potts LRO appears, accompanying the binding of nematic vortices. In the nematic regime, however, the intercomponent $Z_3$ Potts LRO undergoes a two-stage melting process. An intermediate Potts liquid phase emerges between the Potts ordered and disordered phases, characterized by an algebraic correlation with formation of charge-neutral pairs of both hexatic and nematic vortices. These two-stage phase transitions are associated with the proliferation of the domain walls and vortices of the relative $Z_3$ Potts variable, respectively. Our results thus provide a prototype example of two-stage melting of a two-dimensional LRO driven by multiple topological defects.

The Berry curvature plays a key role in the magnetic transport of topological materials. Yet, it is not clear whether the Berry curvature by itself can give rise to universal transport phenomena with specific scaling behaviors. In this work, based on the semiclassical Boltzmann formalism and the symmetry analysis, we show that the noncentrosymmetric distribution of the Berry curvature generally results in linear magnetoresistivity and thermoconductivity both exhibiting the $B$-scaling behavior. We then study such kind of topological linear magnetoresistivity in the 2D $\mathrm{M}\text{n}\mathrm{B}{\text{i}}_2\mathrm{T}{\text{e}}_4$ flakes and the 3D spin-orbit-coupled electron gas, the former showing good agreement with the experimental observations. The difference between our mechanism and the conventional anisotropic magnetoresistance is elucidated. Our theory proposes a universal scenario for the topological linear magnetoresistivity and thermoconductivity and predicts such effects to occur in various materials, which also provides a reasonable explanation for the recent observations of linear magnetoresistivity.

The band structure of $\beta \text{−}{\mathrm{LiGaO}}_2$ is calculated using the quasiparticle self-consistent $\mathrm{QS}G\widehat{W}$ method where the screened Coulomb interaction $\widehat{W}$ is evaluated including electron-hole interaction ladder diagrams and $G$ is the one-electron Green's function. Improved convergence compared to previous calculations leads to a significantly larger band gap of about 7.0 eV. However, exciton binding energies are found to be large and lead to an exciton gap of about 6.0 eV if also a zero-point-motion correction of about $-0.4$ eV is included. These results are in excellent agreement with recent experimental results on the onset of absorption. Besides the excitons observed thus far, the calculations indicate the existence of a Rydberg-like series of exciton excited states, which is however modified from the classical Wannier exciton model by the anisotropies of the material and the more complex mixing of Bloch states in the excitons resulting from the Bethe-Salpeter equation. The exciton fine structure and the exciton wave functions are visualized and analyzed in various ways.

A wave-packet time evolution method, based on the split-operator technique, is developed to investigate the scattering of quasiparticles at a normal-superconductor interface of arbitrary profile and shape. As a practical application, we consider a system where low-energy electrons can be described as Dirac particles, which is the case for most two-dimensional materials, such as graphene and transition-metal dichalcogenides. However, the method is easily adapted for other cases such as electrons in few-layer black phosphorus or any Schrödinger quasiparticles within the effective mass approximation in semiconductors. We employ the method to revisit Andreev reflection in mono-, bi-, and trilayer graphene, where specular- and retro-reflection cases are observed for electrons scattered by a steplike superconducting region. The effect of opening a zero-gap channel across the superconducting region on the electron and hole scattering is also addressed, as an example of the versatility of the technique proposed here.

In equilibrium planer systems of Hall electrons, such as GaAs heterostructures and graphene, support two species of current counterflowing along the system edges, as observed recently in experiment using a nanoscale magnetometer. We examine distinct origins and distinctive features of these equilibrium currents, with the Coulombic many-body effects taken into account, and derive their real-space distributions. Our basic tool of analysis is a reformulation of quantum Hall systems as a $W_{\infty }$ gauge theory, which allows one to diagonalize the total Hamiltonian according to the resolutions of external probes. These equilibrium currents are deeply tied to the orbital magnetization in quantum Hall systems. Special attention is drawn to the case of graphene, especially the neutral $(\nu =0)$ ground state and its intrinsic diamagnetic response that combines with the equilibrium currents to govern the orbital magnetization and its oscillations with filling.

We calculate reflectivities of dynamically compressed water, water-ethanol mixtures, and ammonia at infrared and optical wavelengths with density functional theory and molecular dynamics simulations. The influence of the exchange-correlation functional on the results is examined in detail. Our findings indicate that the consistent use of the HSE hybrid functional reproduces experimental results much better than the commonly used PBE functional. The HSE functional offers not only a more accurate description of the electronic band gap but also shifts the onset of molecular dissociation in the molecular dynamics simulations to significantly higher pressures. We also highlight the importance of using accurate reference standards in reflectivity experiments and reanalyze infrared and optical reflectivity data from recent experiments. Thus, our combined theoretical and experimental work explains and resolves lingering discrepancies between calculations and measurements for the investigated molecular substances under shock compression.

Entanglement comes in different forms, some more complex than others. In this paper we study the transitions of entanglement complexity in an exemplary family of states—the Rokhsar-Kivelson-sign wavefunctions—whose degree of entanglement is controlled by a single parameter. This family of states is known to feature a transition between a phase exhibiting volume-law scaling of entanglement entropy and a phase with subextensive scaling of entanglement, reminiscent of the many-body-localization transition of disordered quantum Hamiltonians. We study the singularities of the Rokhsar-Kivelson-sign wavefunctions and their entanglement complexity across the transition using several tools from quantum information theory: fidelity metric, entanglement spectrum statistics, entanglement entropy fluctuations, stabilizer Rényi entropy, and the performance of a disentangling algorithm. Across the whole volume-law phase the states feature universal entanglement spectrum statistics. Yet a “superuniversal” regime appears for small values of the control parameter in which all metrics become independent of the parameter itself, the entanglement entropy as well as the stabilizer Rényi entropy appear to approach their theoretical maximum, the entanglement fluctuations scale to zero as in output states of random universal circuits, and the disentangling algorithm has essentially null efficiency. All these indicators consistently reveal a complex pattern of entanglement. In the sub-volume-law phase, on the other hand, the entanglement spectrum statistics is no longer universal, entanglement fluctuations are larger and exhibiting a nonuniversal scaling, and the efficiency of the disentangling algorithm becomes finite. Our results, based on model wavefunctions, suggest that a similar combination of entanglement scaling properties and of entanglement complexity features may be found in high-energy Hamiltonian eigenstates—a very strong candidate being offered by the many-body localization transition of disordered lattice-spin models.

The magnetic field-temperature phase diagrams and spin-spin correlations of quasi-two-dimensional ferromagnetic ${\mathrm{Cr}}_2{\mathrm{Ge}}_2{\mathrm{Te}}_6$ and ${\mathrm{Cr}}_2{\mathrm{Si}}_2{\mathrm{Te}}_6$ and antiferromagnetic $\mathrm{Mn}{\mathrm{Bi}}_2{\mathrm{Te}}_4$ are investigated and compared by a sensitive composite magnetoelectric method. The phase diagrams of ${\mathrm{Cr}}_2{\mathrm{Ge}}_2{\mathrm{Te}}_6$ and ${\mathrm{Cr}}_2{\mathrm{Si}}_2{\mathrm{Te}}_6$ disclose a triple point around the Curie temperature where three phases coexist, for both $H\parallel c$ axis and $ab$ plane configurations. In contrast, a triple/tricritical point is found in $\mathrm{Mn}{\mathrm{Bi}}_2{\mathrm{Te}}_4$ only for the $H\parallel c$ axis configuration. Anomalous enhancement of magnetoelectric signals is observed near the triple points of ${\mathrm{Cr}}_2{\mathrm{Ge}}_2{\mathrm{Te}}_6$ and ${\mathrm{Cr}}_2{\mathrm{Si}}_2{\mathrm{Te}}_6$, suggesting significant enhancement of ferromagnetic spin-spin correlations at this point. Nevertheless, no short-range spin-spin correlation is found in $\mathrm{Mn}{\mathrm{Bi}}_2{\mathrm{Te}}_4$ above the Néel temperature.

Zero-point quantum fluctuations of a Néel order can produce effective interactions between quasi-orphan spins weakly coupled to the lattice. On the $\sqrt{3}\times \sqrt{3}$-distorted triangular lattice, this phenomenon leads to a correlated partially disordered phase. In this article, we use matrix product state methods to study a similar model: the $S=1/2$ stuffed square lattice. Tuning the exchange amplitudes we go from a square lattice plus orphan central spins at $J^{\prime }/J=0$, to the union jack lattice at $J^{\prime }/J=1$, and a square lattice including all spins at $J/J^{\prime }=0$. We calculate the complete antiferromagnetic phase diagram, dominated by ferrimagnetic and Néel orders, and compare it with existing results. Most importantly, we find a partially disordered phase in the weakly frustrated regime. In this phase, the Néel order from the square lattice is unaffected, while the central spins form a collective state with exponentially decaying double-striped correlations. We also study the role of quantum fluctuations by introducing an ordering staggered magnetic field on the square sublattice and find that the central spins order ferromagnetically when fluctuations from the Néel order are suppressed.

We revisit the quantitative analysis of the ultrafast magnetoacoustic experiment in a freestanding nickel thin film by Kim and Bigot [J.-W. Kim and J.-Y. Bigot, Phys. Rev. B 95, 144422 (2017)] by applying our recently proposed approach of magnetic and acoustic eigenmode decomposition. We show that the application of our modeling to the analysis of time-resolved reflectivity measurements allows for the determination of amplitudes and lifetimes of standing perpendicular acoustic phonon resonances with unprecedented accuracy. The acoustic damping is found to scale as $\propto {\omega }^2$ for frequencies up to 80 GHz, and the peak amplitudes reach ${10}^{-3}$. The experimentally measured magnetization dynamics for different orientations of an external magnetic field agrees well with numerical solutions of magnetoelastically driven magnon harmonic oscillators. Symmetry-based selection rules for magnon-phonon interactions predicted by our modeling approach allow for the unambiguous discrimination between spatially uniform and nonuniform modes, as confirmed by comparing the resonantly enhanced magnetoelastic dynamics simultaneously measured on opposite sides of the film. Moreover, the separation of timescales for (early) rising and (late) decreasing precession amplitudes provide access to magnetic (Gilbert) and acoustic damping parameters in a single measurement.

Using high-resolution extreme ultraviolet resonant inelastic x-ray scattering (EUVRIXS) spectroscopy at the Cu $M$-edge, we observed doping dependent spectral shifts of interorbital ($dd$) excitations of $\mathrm{Y}{\mathrm{Ba}}_2{\mathrm{Cu}}_3{\mathrm{O}}_{7-y}$ and ${\mathrm{La}}_{2-x}{\mathrm{Sr}}_x\mathrm{Cu}{\mathrm{O}}_4$. With increasing the hole doping level from undoped to optimally doped superconducting compositions, the leading edge of $dd$ excitations is found to shift towards lower energy loss in a roughly linear trend that is irrespective of the cuprate species. The magnitude of the energy shift can be explained by including a 0.15 eV Coulomb attraction between $\mathrm{Cu}3d\left(x^2\text{−}{y}^2\right)$ electrons and the doped holes on the surrounding oxygens in the atomic multiplet calculations. The consistent energy shift between distinct cuprate families suggests that this intersite Coulomb interaction energy scale is relatively material independent, and provides an important reference point for understanding charge density wave phenomena in the cuprate phase diagram.

Zinc ferrite (${\mathrm{ZnFe}}_{\text{2}}{\mathrm{O}}_{\text{4}}$) epitaxial thin films were grown by reactive magnetron sputtering on ${\mathrm{MgAl}}_{\text{2}}{\mathrm{O}}_{\text{4}}$ and ${\mathrm{Al}}_{\text{2}}{\mathrm{O}}_{\text{3}}$ substrates varying a range of preparation parameters. The resulting structural and magnetic properties were investigated using a range of experimental techniques confirming epitaxial growth of ${\mathrm{ZnFe}}_{\text{2}}{\mathrm{O}}_{\text{4}}$ with the nominal stoichiometric composition and long-range magnetic order at and above room temperature. The main preparation parameter influencing the temperature $T_f$ of the bifurcation between $M\left(T\right)$ curves under field-cooled and zero-field-cooled conditions was found to be the growth rate of the films, while growth temperature or the Ar:${\mathrm{O}}_2$ ratio did not systematically influence $T_f$. Furthermore $T_f$ was found to be systematically higher for ${\mathrm{MgAl}}_{\text{2}}{\mathrm{O}}_{\text{4}}$ as substrate and $T_f$ extends to above room temperature. While in some samples $T_f$ seems to be more likely correlated with superparamagnetism, the highest $T_f$ occurs in ${\mathrm{ZnFe}}_{\text{2}}{\mathrm{O}}_{\text{4}}$ epitaxial films where experimental signatures of magnetic glassiness can be found. Element-selective x-ray magnetic circular dichroism measurements aim at associating the magnetic glassiness with the occurrence of a different valence state and lattice site incorporation of Fe pointing to a complex interplay of various competing magnetic interactions in ${\mathrm{ZnFe}}_{\text{2}}{\mathrm{O}}_{\text{4}}$.

Understanding the spin-relaxation mechanism of single adatoms is an essential step towards creating atomic magnetic memory bits or even qubits. Here, we present an essentially parameter-free theory by combining ab initio electronic and vibrational properties with the many-body nature of atomic states. Our calculations account for the millisecond spin lifetime measured recently on Fe adatoms on MgO/Ag(100) and reproduce the dependence on the number of decoupling layers and the external magnetic field. We show how the atomic interaction with the environment should be tuned in order to enhance the magnetic stability, and propose a clear fingerprint for experimentally detecting a localized spin-phonon excitation.

We theoretically study the interaction of spin waves and a domain wall in a quasi-one-dimensional easy-cone ferromagnet. The gapless spin waves on top of a domain wall are found to exhibit finite reflection in contrast to the well-known perfect transmission of gapful spin waves in easy-axis magnets. Based on the obtained scattering properties, we study the thermal-magnon-driven dynamics of a domain wall subjected to a thermal bias within the Landauer-Büttiker formalism, where transmitted magnons are shown to exert the magnonic torque on the domain wall and thereby drive it with the velocity linear to the applied thermal bias. The peculiar gapless nature of spin waves in easy-cone magnets enables the thermally driven domain-wall motion even at low temperatures, differing from the easy-axis case where the domain-wall velocity is exponentially suppressed at low temperatures. Our work suggests that easy-cone magnets can serve as a useful platform to study the interaction of gapless spin waves and nonlinear excitations and thereby realize low-temperature magnon-related phenomena.

$\mathrm{SrIr}{\mathrm{O}}_3/{\mathrm{La}}_{0.7}{\mathrm{Sr}}_{0.3}\mathrm{Mn}{\mathrm{O}}_3$ heterostructure including contact of $3d-5d$ materials with strong spin-orbit interaction in $\mathrm{SrIr}{\mathrm{O}}_3$ was fabricated by rf magnetron sputtering at high temperature. The epitaxial growth of the thin films in heterostructure by a cube-on-cube mechanism was confirmed by x-ray diffraction and transmission electron microscopy analysis. We present results of experimental studies of spin current and spin mixing conductance of the heterostructures measured under spin pumping at ferromagnetic resonance in wide-frequency band 2–20 GHz. Taking into account the contribution of anisotropic magnetoresistance the spin current was estimated as 1/3 of the total response. We show that both real and imaginary parts of spin mixing conductance are valuable for heterostructures with spin-orbit interaction in $\mathrm{SrIr}{\mathrm{O}}_3$. The spin Hall magnetoresistance of the heterostructure was evaluated from angular dependencies of either longitudinal or transverse magnetoresistance measured in planar Hall configuration. The influence of anisotropic magnetoresistance of ${\mathrm{La}}_{0.7}{\mathrm{Sr}}_{0.3}\mathrm{Mn}{\mathrm{O}}_3$ film was taken into account as well. The spin Hall angle estimated from measurements of transverse magnetoresistance was found much higher than that obtained for interfaces with often-used spin-orbit interaction material like platinum.

Given a critical quantum spin chain described by a conformal field theory (CFT) at long distances, it is crucial to understand the universal conformal data. One most important ingredient is the operator product expansion (OPE) coefficients, which describe how operators fuse into each other. It has been proposed in [Zou and Vidal, Phys. Rev. B 105, 125125 (2022)] that the OPE coefficients can be computed from overlaps of low-energy wave functions of the spin chain. In this paper, we establish that all conformal data including central charge, conformal dimensions, and OPE coefficients are encoded in the wave-function overlaps, with universal finite-size corrections that depend on the operator content of the cyclic orbifold CFT. Thus this method allows us to numerically compute all the conformal data based solely on the low-energy eigenstates. The predictions are verified in the Ising and XXZ model. As an application, we study the recently proposed Haagerup model built from the Haagerup fusion category. We find that the CFT has central charge $c\approx 2.1$ and the lowest spin-1 operator in the twisted sector has scaling dimension $1<{\mathrm{\Delta }}_J\le 1.4$.

Understanding the correlation effects in unconventional topological materials, in which the fermion excitations take unusual dispersion, is an important topic in recent condensed matter physics. We study the influence of short-range four-fermion interactions on three-dimensional semi-Dirac semimetal with an unusual fermion dispersion that is linear along two directions and quadratic along the third one. Based on renormalization group theory, we find all of 11 unstable fixed points including five quantum critical points, five bicritical points, and one tricritical point. The physical essences of the quantum critical points are determined by analyzing the susceptibility exponents for all of the source terms in particle-hole and particle-particle channels. We also verify phase diagrams of the system in the parameter space through numerically studying the flows of the four-fermion coupling parameters and behaviors of the susceptibility exponents. These results are helpful for us to understand the physical properties of candidate materials for three-dimensional semi-Dirac semimetal such as ${\mathrm{ZrTe}}_5$.

While the anomalous Hall effect takes place typically in ferromagnets with finite magnetization, large anomalous Hall conductivity in noncollinear antiferromagnetic systems has been recently observed and attracted much attention. In this paper, we predict the anomalous Hall effect in perovskite ${\mathrm{CaCrO}}_3$ as a representative of collinear antiferromagnetic materials. Our result shows that the $C$-type antiferromagnetic ordering generates the sizable anomalous Hall conductivity. Based on symmetry analyses, we show that the antiferromagnetic order parameter belongs to the same irreducible representation as the ferromagnetic order parameter in the nonsymmorphic space group, allowing the nonvanishing Berry curvatures in $k$ space. By performing first-principles density-functional theory calculations, we find that the Berry-curvature “hot spots” lie along the gapped nodal lines where spin-orbit coupling induces the spin splitting of Cr-$3d$ bands near the Fermi energy and enhances the anomalous Hall effect in ${\mathrm{CaCrO}}_3$.