Intermetallics are an important playground to stabilize a large variety of physical phenomena, arising from their complex crystal structure. The ease of their chemical tunabilty makes them suitable platforms to realize targeted electronic properties starting from the symmetries hidden in their unit cell. Here, we investigate the family of the recently discovered intermetallics $M{\mathrm{Co}}_2{\mathrm{Al}}_9$ ($M=\text{Sr}$, Ba) and we unveil their electronic structure. By using angle-resolved photoelectron spectroscopy and density functional theory calculations, we discover the existence of Dirac-like dispersions as ubiquitous features in this family, coming from the hidden kagome and honeycomb symmetries embedded in the unit cell. Finally, from calculations, we expect that the spin-orbit coupling is responsible for opening energy gaps in the electronic structure spectrum, which also affects the majority of the observed Dirac-like states. Our study constitutes an experimental observation of the electronic structure of $M{\mathrm{Co}}_2{\mathrm{Al}}_9$ and proposes these systems as hosts of Dirac-like physics with intrinsic spin-orbit coupling. The latter effect suggests $M{\mathrm{Co}}_2{\mathrm{Al}}_9$ as a future platform for investigating the emergence of nontrivial topology.

Recently, the electronic analogy of the anomalous spatial shift, including Goos-Hänchen and Imbert-Fedorov effects, has been attracting widespread interest. Current research on the anomalous spatial shift in interface electronic reflection is based on the paradigm of linear approximation, under which the center position of the incident and reflected beams are obtained by expanding the phases of relevant basis states and scattering amplitudes to the first order of incident momentum. However, in a class of normal cases, the linear approximation leads to divergent spatial shifts in reflection for certain incident angles, even though the corresponding reflection possibility is finite. In this paper, we show that these nonphysical results are caused by an abrupt change in the number of the propagating states at critical parameters, and can be resolved by calculating the center positions of the scattering beams beyond the linear approximation. Moreover, we find that the beam width has an important influence on the spatial shift near the critical angles. We demonstrate our idea via concrete calculations of Goos-Hänchen and Imbert-Fedorov shift on two representative models. These results provide a deeper understanding of the anomalous spatial shift in calculations.

The intermetallic compound ${\mathrm{TlBi}}_2$ crystallizes in the ${\mathrm{MgB}}_2$ structure and becomes superconducting below 6.2 K. Considering that both Tl and Bi have heavy atomic masses, it is puzzling why ${\mathrm{TlBi}}_2$ is a conventional phonon-mediated superconductor. We have performed comprehensive first-principles calculations of the electronic structures, the phonon dispersions, and the electron-phonon couplings for ${\mathrm{TlBi}}_2$. The $6p$ orbitals of bismuth dominate over the states near the Fermi level, forming strong intralayer $p_{x/y}$ and interlayer $p_z \sigma$ bonds which are known to have strong electron-phonon coupling. In addition, the large spin-orbit coupling interaction in ${\mathrm{TlBi}}_2$ increases significantly its electron-phonon coupling constant. As a result, ${\mathrm{TlBi}}_2$, with a logarithmic phonon frequency average one-tenth that of ${\mathrm{MgB}}_2$, is a phonon-mediated superconductor.

Here, we quantitatively determine the impact of III-V/Si interface atomic configuration on the wetting properties of the system. Based on a description at the atomic scale using density functional theory, we first show that it is possible to determine the absolute interface energies in heterogeneous materials systems. A large variety of absolute GaP surface energies and GaP/Si interface energies are then computed, confirming the large stability of charge-compensated III-V/Si interfaces with an energy as low as $23\mathrm{meV}/{\AA }^2$. While stable compensated III-V/Si interfaces are expected to promote complete wetting conditions, it is found that this can be easily counterbalanced by the substrate initial passivation, which favors partial wetting conditions.

Recently, antiferromagnetic (AFM) materials have attracted rapid attention, because they are considered as outstanding candidates to replace the widely used ferromagnets in the next generation of spintronics. We propose a magnetoresistance model based on the quantum anomalous Hall effect in an AFM system, which is protected by the topological Chern number. By regulating the AFM exchange field and an electric field, the system can be controlled between the quantum spin Hall insulator (QSHI) phases and the quantum anomalous Hall insulator (QAHI) phases. As a result, a QAHI/QSHI/QAHI junction can be formed. In the QAHI region, the spin orientation of the chiral edge state can be manipulated by tuning the AFM exchange field and the electric field. Therefore, the spin directions of two QAHIs in the junction can have parallel and antiparallel configurations. The conductances of two configurations offered by chiral edge states are significantly different, and this is a magnetoresistance effect that can be electrically controlled. Because of the topological invariance, the magnetoresistance plateaus are robust to the size effect and the disorder.

H-phase hexagonal two-dimensional lattices have been extensively studied in the field of valleytronics. In contrast, their counterparts in the T phase have received relatively less attention due to the presence of inversion symmetry, which limits the potential for generating an anomalous valley Hall effect (AVHE). However, the Janus and bilayer stacking structures provide additional prospects to discover extra candidates. Herein, we employed first-principles calculations to predict the stacking-dependent AVHE in bilayer Janus VSCl. Owing to the intrinsic net magnetic moment, the valleys of the monolayer Janus VSCl are spontaneously polarized by out-of-plane magnetization, obviating the need for the external magnetic substrate. This valley polarization can be maintained through specific stacking configurations, allowing electrons with identical spins but different valley indices to flow toward the same side, which results in a significant AVHE and the emergence of a spin current. Notably, we found that interlayer coupling can selectively enhance or diminish the Berry curvatures of the two nonequivalent valleys, even without any external strain. Additionally, the results are effectively explicable through the analysis of our proposed model. In this paper, we present a promising material and put forth ideas for uncovering valleytronic candidates.

We study the time evolution of geometric phases of one-dimensional topological models under the quench dynamics. Taking the Creutz ladder model as an example, it is found that the Berry phase is fixed as the parameter is suddenly tuned across the topological phase boundary, given that the inversion symmetry of the model is preserved. At finite temperature, the Uhlmann phase displays abrupt jumps between the two quantized values, which indicates the topological transition at certain times after the quench. Both the Berry and Uhlmann phase will deviate from quantized values if the inversion symmetry if the model is broken.

Metasurfaces based on phase change materials are widely used for the controllable on-demand modification of properties of a device at the postfabrication stage. We report the fabrication of a switchable Ge-Sb-Te (GST)-based metasurface with a submicron period by magnetron sputtering with electron beam lithography postprocessing. We provide theoretical and experimentally measured angle-resolved reflection spectra of such metasurfaces. In these spectra, we observe magnetic dipole resonance features, which significantly differ for two different GST states, and Rayleigh anomalies, whose spectral position remains unchanged during the phase transition. We demonstrate the optical response of these metasurfaces to be strongly modulated under GST phase transition in the telecom wavelength range.

The application of pressure as well as the successive substitution of Ru with Fe in the hidden order (HO) compound ${\mathrm{URu}}_2{\mathrm{Si}}_2$ leads to the formation of the large-moment antiferromagnetic phase. Here, we investigate the substitution series ${\mathrm{URu}}_{2-x}{\mathrm{Fe}}_x{\mathrm{Si}}_2$ from $x=0.0$ to 2.0 by U $4f$ core-level photoelectron spectroscopy and observe nonmonotonic changes in the spectra. The initial increase and subsequent decrease in the spectral weight of the $4f$ core-level satellite with increasing $x$ stands for a nonmonotonic $5f$ filling across the substitution series. The competition of chemical pressure and increase in the density of states at the Fermi energy, both due to substitution of Ru with Fe, can explain such behavior. An extended Doniach phase diagram including the $x$ dependence of the density of states is proposed. Also in ${\mathrm{URu}}_{2-x}{\mathrm{Fe}}_x{\mathrm{Si}}_2$ the ground state is a singlet or quasidoublet state consisting of two singlets. Hence, the formation of magnetic order in the ${\mathrm{URu}}_{2-x}{\mathrm{Fe}}_x{\mathrm{Si}}_2$ substitution series must be explained within a singlet magnetism model.

We investigated the element-specific electronic states and magnetic properties of ferromagnetic superconductor UCoGe and Ru-substituted $\mathrm{U}\left({\mathrm{Co}}_{0.88}{\mathrm{Ru}}_{0.12}\right)\mathrm{Ge}$ using soft x-ray magnetic circular dichroism (XMCD) experiments at the absorption edges of U $N_{4,5}$, Co $L_{2,3}$, and Ge $L_{2,3}$. YCoGe, a nonmagnetic compound without the $5f$ electrons, was also examined as a reference material. The shapes of the XMCD spectra of UCoGe at the U $N_5$ and Ge $L_{2,3}$ edges are indistinguishably similar to those of $\mathrm{U}\left({\mathrm{Co}}_{0.88}{\mathrm{Ru}}_{0.12}\right)\mathrm{Ge}$. On the other hand, the XMCD spectral shape at the Co $L_2$ edge is very peculiar and is changed by the presence of the U $5f$ electrons and the Ru substitution. From the sum rule analysis for the XMCD spectra, it was found that the magnetic moments of the U $5f$ and Co $3d$ electrons in UCoGe and $\mathrm{U}\left({\mathrm{Co}}_{0.88}{\mathrm{Ru}}_{0.12}\right)\mathrm{Ge}$ are aligned in the same direction under the present experimental conditions: $T$ = 5.5–50 K and ${\mu }_{0}H$ = 0–10 T. Furthermore, not only in UCoGe and $\mathrm{U}\left({\mathrm{Co}}_{0.88}{\mathrm{Ru}}_{0.12}\right)\mathrm{Ge}$ but even in the case of YCoGe, the Co $3d$ electrons have a large orbital magnetic moment, suggesting that the Co $3d$ electrons in these compounds are in a low-symmetry electronic environment originally. Through the $T$ and ${\mu }_{0}H$ dependence of the XMCD intensity, it was revealed that the magnetic properties at the Co site are not simply induced by the magnetism at the U site and that the Co $3d$ electrons play an important role in the stability of ferromagnetism. The present findings clearly demonstrate that the contribution of not only the U $5f$ electrons but also the Co $3d$ electrons is very crucial to understanding the complex physical properties of the $\mathrm{U}\left({\mathrm{Co}}_{1-x}{\mathrm{Ru}}_x\right)\mathrm{Ge}$ system.

Although a parent Hamiltonian for the Laughlin $1/3$ wave function has been long known in terms of the Haldane pseudopotentials, no parent Hamiltonians are known for the lowest-Landau-level projected wave functions of the composite fermion theory at $n/(2n+1)$ with $n\ge 2$. If one takes the two lowest Landau levels to be degenerate, the Trugman-Kivelson interaction produces the unprojected 2/5 wave function as the unique zero energy solution. If the lowest three Landau levels are assumed to be degenerate, the Trugman-Kivelson interaction produces a large number of zero energy states at $\nu =3/7$. We propose that adding an appropriately constructed three-body interaction yields the unprojected $3/7$ wave function as the unique zero energy solution and report extensive exact diagonalization studies that provide strong support to this proposal.

The work is devoted to the formation energy calculations of intrinsic defects in silicon based on the $GW$ method and the Galitskii-Migdal formula. Two methods for calculating the electronic response function are applied. The first one uses direct integration over frequency to determine the response function. The diagonal form of the spectral function is the only assumption within the random phase approximation (RPA) framework, but the supercell calculations are very time consuming. Therefore, we propose the method in which the response function is calculated in the plasmon pole approximation, and the $GW$ contribution to the exchange-correlation energy is taken with a certain mixing constant. The value of the constant is found from the correspondence with experimental data. This makes it possible to obtain accuracy comparable to the first method at significantly lower computational costs. The described method is used to calculate the formation energy of the neutral self-interstitial, vacancy, and two divacancy structures in supercells of 214–217 silicon atoms.

We analyze the time evolution of a quantum dot which is proximized by a large-gap superconductor and weakly probed using the charge and heat currents into a wide-band metal electrode. We map out the full time dependence of these currents after initializing the system by a switch. We find that due to the proximity effect there are two simple yet distinct switching procedures which initialize a nonstationary mixture of the gate-voltage-dependent eigenstates of the proximized quantum dot. We find in particular that the ensuing time-dependent heat current is a sensitive two-particle probe of the interplay of strong Coulomb interaction and induced superconducting pairing. The pairing can lead to a suppression of charge and heat current decay which we analyze in detail. The analysis of the results makes crucial use of analytic formulas obtained using fermionic duality, a “dissipative symmetry” of master equations describing this class of open systems.

The isotropic Heisenberg chain represents a particular case of an integrable many-body system exhibiting superdiffusive spin transport at finite temperatures. Here, we show that this model has distinct properties also at finite magnetization $m\ne 0$, even upon introducing the SU(2) invariant perturbations. Specifically, we observe nonmonotonic dependence of the diffusion constant ${\mathcal{D}}_0\left(\mathrm{\Delta }\right)$ on the spin anisotropy $\mathrm{\Delta }$, with a pronounced maximum at $\mathrm{\Delta }=1$. The latter dependence remains true also in the zero magnetization sector, with superdiffusion at $\mathrm{\Delta }=1$ that is remarkably stable against isotropic perturbation (at least in finite-size systems), consistent with recent experiments with cold atoms.

We theoretically propose a strategy to address an individual spin in a large array of spin qubits with a random distribution of $g$ factors by employing a combination of single-qubit and swap gates facilitated by a global microwave field and local exchange pulses. Consequently, only the target qubit undergoes the desired operation and all other qubits return to their original states, even qubits that share the same Larmor frequency as the target. Gate fidelities above 99% can thus be maintained for arrays containing tens of qubits.

The freestanding twisted bilayer graphene (TBG) is unstable, below a critical twist angle ${\theta }_c\sim 3.7^{\circ }$, against a moiré $(2\times 1)$ buckling distortion at $T=0$. Realistic simulations reveal the concurrent unexpected collapse of the bending rigidity, an unrelated macroscopic mechanical parameter. An analytical model connects bending and buckling anomalies at $T=0$, but as temperature rises the former fades, while buckling persists further. The $(2\times 1)$ electronic properties are also surprising. The magic twist angle narrow bands, now eight in number, fail to show zone boundary splittings despite the different periodicity. Symmetry shows how this is dictated by an effective single-valley physics. These structural, critical, and electronic predictions promise to make the freestanding state of TBG especially interesting.

We experimentally study the dynamical modes excited by current-induced spin-orbit torques and the electrostatic gating effect in a three-terminal planar nanogap spin Hall nano-oscillator (SHNO) with a moderate interfacial perpendicular magnetic anisotropy (iPMA). Both quasilinear propagating spin-wave and localized ”bullet” modes are achieved and controlled by varying in-plane magnetic field and dc current. The minimum linewidth shows a linear dependence on the actual temperature of the active area, consistent with the single-mode dynamics described by the nonlinear theory of spin-torque nano-oscillator. The observed electrostatic gating tuning oscillation frequency arises from voltage-controlled magnetic anisotropy and threshold current of SHNO. The latter is related to voltage modification of the nonlinear damping and the interfacial spin-orbit coupling. In contrast to previously observed two-mode coexistence in Py/Pt-based SHNOs with a negligible iPMA, a single coherent spin-wave mode can be achieved by selecting the ferromagnet layer with a suitable iPMA, where nonlinear mode coupling in this nanogap SHNO can be diminished by bringing in the PMA field to compensate the easy-plane shape anisotropy. Moreover, the simulations demonstrate that the experimentally observed current-driven auto-oscillation modes are closely associated with the nonlinear damping and mode coupling, which can be tuned by the effective PMA coefficient. The demonstrated nonlinear mode coupling mechanism and electrical control approach of spin-wave modes could provide the clue to facilitate the implementation of the mutual synchronization map for neuromorphic computing applications in SHNO array networks.

We show that competition between local interactions in monoaxial chiral magnets provides the stability of two-dimensional solitons with identical energies but opposite topological charges. These skyrmions and antiskyrmions represent metastable states in a wide range of parameters above the transition into the saturated ferromagnetic phase. The symmetry of the underlying micromagnetic functional gives rise to soliton zero modes allowing efficient control of their translational movement by the frequency of the circulating external magnetic field. We also discuss the role of demagnetizing fields in the energy balance between skyrmions and antiskyrmions and in their stability.

The magnetocaloric effect (MCE) plays a major role in magnetic refrigeration. However, a large MCE near room temperature has rarely been observed in the fast-growing family of two-dimensional (2D) materials. Using 2D non–van der Waals crystals, herein we design an intrinsic and physically realistic system to achieve a large MCE. Based on first-principles calculations, we identify that 2D MnCoAs is a robust ferromagnetic metal, whose specific heat shows anomalous bimodal behavior. The MCE in 2D MnCoAs generates a Curie temperature of 214–221 K, a magnetic entropy change of $1.4-4.3\mathrm{J}\mathrm{k}{\mathrm{g}}^{-1}{\mathrm{K}}^{-1}$, a relative cooling power of $28.4-244.5\mathrm{J}\mathrm{k}{\mathrm{g}}^{-1}$, and a full width at half maximum of the entropy change peak of 20–57 K for a magnetic field change of 1–7 T. For comparison, the value of magnetic entropy change is $0-0.2\mathrm{J}\mathrm{k}{\mathrm{g}}^{-1}{\mathrm{K}}^{-1}$ in bulk MnCoAs. Obviously, the reduced dimensionality leads to a significant improvement in the MCE. In addition, 2D MnCoAs is highly ductile, which is conducive to magnetic refrigeration cycling stability. We also show that a 2D MnCoAs crystal can be grown on a Si (001) substrate while it retains its MCE value, paving an avenue to the desired goal of on-chip cooling. Our results provide not only an alternative MCE thin film for cooling applications in nanodevices, but also a fundamental understanding of the impact of reduced dimensionality on MCE.

Classical theories of crystal nucleation and growth from the liquid assume activated processes that are interface limited, with the atoms individually joining the growing interface by jumps that occur at a rate that is determined by the diffusion coefficient in the liquid phase. These assumptions are in contradiction with the results of molecular dynamics studies that are presented here for supercooled Ni and ${\mathrm{Al}}_{20}{\mathrm{Ni}}_{60}{\mathrm{Zr}}_{20}$. Instead of diffusion-based attachment across the interface, atoms join the interface by making small changes so as to match the orientational order parameter of the nucleating crystal. Further, instead of joining individually multiple atoms join cooperatively, with the number of cooperative atoms increasing with decreasing temperature.