Alloying stands out as a pivotal technological method employed across various compounds, be they metallic, magnetic, or semiconducting, serving to fine-tune their properties to meet specific requirements. Ternary semiconductors represent a prominent example of such alloys. They offer fine-tuning of electronic bands, the band gap in particular, thus granting the technology of semiconductor heterostructures devices, key elements in current electronics and optoelectronics. In the realm of magnetically ordered systems, akin to electronic bands in solids, spin waves exhibit characteristic dispersion relations, featuring sizable magnon gaps in many antiferromagnets. The engineering of the magnon gap constitutes a relevant direction in current research on antiferromagnets, aiming to leverage their distinct properties for terahertz technologies, spintronics, or magnonics. In this study, we showcase the tunability of the magnon gap across the terahertz spectral range within an alloy comprising representative semiconducting van der Waals antiferromagnets ${\mathrm{FePS}}_3$ and ${\mathrm{NiPS}}_3$. These constituents share identical in-plane crystal structures, magnetic unit cells, and the direction of the magnetic anisotropy, but differ in the amplitude and sign of the latter. Altogether these attributes result in the wide tunability of the magnon gap in the ${\mathrm{Fe}}_{1-x}{\mathrm{Ni}}_x{\mathrm{PS}}_3$ alloy in which the magnetic order is imposed by the stronger, perpendicular anisotropy of iron.

The magnetization dynamics of two skyrmions with antiparallel vortex rotations on a nanowire substrate were investigated using micromagnetic simulations. When positioned in proximity, the skyrmions exhibit attractive interactions that decrease their separation distance. This interaction leads to a magnetic energy transition, resulting in the fusion of the two skyrmions into a single connected entity. Applying a static magnetic field aligned with the magnetization direction of the skyrmion cores causes this connected structure to expand, increasing the distance between their cores. Conversely, exposing the connected skyrmions to a specific alternating magnetic field induces resonant oscillations in the core-to-core distance, with the resonance frequency decreasing as the field amplitude increases. The effective mass of the connected skyrmions at resonance is calculated using the resonance frequency. Notably, excessively high amplitudes can cause these oscillations to converge the skyrmions excessively, leading to their annihilation. In simulations involving both static and alternating magnetic fields, separation of the connected skyrmions was not observed. These findings have potential implications for the advancement of technologies utilizing skyrmion numbers for innovative applications.

Exceptional points with coalescence of eigenvalues and eigenvectors are spectral singularities in the parameter space, achieving which often needs fine-tuning of parameters in quantum systems. We predict a persistent realization of nodal magnon-photon polariton, i.e., a polariton of long wavelength without any gap splitting in a thin ferromagnetic insulator film sandwiched by two normal metals, which persistently exists when the ferromagnet is sufficiently thick $\sim 100$ nm due to the joint effect of dissipation and dissipative coupling. We perform the model calculation beyond the perturbation theory using a classical approach, develop a quantum scheme able to account for the Ohmic dissipation, and find ultrastrong coupling with coupling strength comparable to the bare magnon frequency. Via revealing a simple conversion relation, we extend this formalism to superconductors and predict the gap opened by the ultrastrong coupling strongly depends on the direction of polariton propagation. Our findings may help search for robust non-Hermitian topological phases in magnonic and spintronic devices.

We report the growth and physical properties of high-quality needle-shaped $\mathrm{R}{\mathrm{e}}_3\mathrm{G}{\mathrm{e}}_7$ single crystal with various characterizations. It exhibits a gapped metal-insulator (MI)-like phase transition with evident Shubnikov–de Haas oscillation of low-$T$ electrical resistivity. The superconducting phase diagram was revisited by measuring the electrical resistivity in a cubic anvil cell (CAC) under various hydrostatic pressures up to 12 GPa. Unlike the results of single crystals in a diamond anvil cell (DAC) and polycrystalline in CAC, the gapped MI-like phase transition of single-crystal $\mathrm{R}{\mathrm{e}}_3\mathrm{G}{\mathrm{e}}_7$ evolves into three charge density wave (CDW)-like ones, which are reduced gradually by applied pressure and then collapse at several critical pressures; approaching the CDW-like quantum criticality, two distinct superconducting phases emerge and transit from one to another in a narrow pressure range; the significant increase in superconducting width indicates their strong competition. By combining density functional theory calculations, the origin of the melting MI-like transition caused by pressure and Ga doping, as well as the competitive CDW-like phase transitions and distinct superconductivity, are discussed.

A mechanism to deterministically prepare a nanowire Josephson junction in an odd parity state is proposed. The mechanism involves population of two Andreev levels by a resonant microwave drive breaking a Cooper pair, and a subsequent ionization of one of the levels by the same drive. Robust preparation of the odd state is allowed by a residual Coulomb repulsion in the junction. A similar resonant process can also be used to prepare the junction in the even state. Our theory explains a recent experiment [J. J. Wesdorp et al., Phys. Rev. Lett. 131, 117001 (2023)].

By utilizing a multiorbital periodic Anderson model with parameters obtained from ab initio band structure calculations, combined with degenerate perturbation theory, we derive effective Kondo-Heisenberg and spin Hamiltonians that capture the interaction among the effective magnetic moments. This derivation encompasses fluctuations via both nonmagnetic $4f^0$ and magnetic $4f^2$ virtual states, and its accuracy is confirmed through comparison with experimental data obtained from ${\mathrm{CeIn}}_3$. The significant agreement observed between experimental results and theoretical predictions underscores the potential of deriving minimal models from first-principles calculations for achieving a quantitative description of $4f$ materials. Moreover, our microscopic derivation unveils the underlying origin of anisotropy in the exchange interaction between Kramers doublets, shedding light on the conditions under which this anisotropy may be weak compared to the isotropic contribution.

Structural defects are important for both solid-state chemistry and physics, as they can have a significant impact on chemical stability and physical properties. Here, we identify a vacancy-induced pseudogap formation in antiferromagnetic $\mathrm{C}{\mathrm{r}}_{0.86}\mathrm{ZnSb}$. $\mathrm{C}{\mathrm{r}}_{1-x}\mathrm{ZnSb}$ alloys were studied combining efforts of density functional theory (DFT) calculations and experimental methods to elucidate the effect of vacancies. Detailed analyses (x-ray powder and single-crystal diffraction, transmission and secondary scanning electron microscopy) of $\mathrm{C}{\mathrm{r}}_{1-x}\mathrm{ZnSb},0<x<0.20$, prompts $\mathrm{C}{\mathrm{r}}_{0.86}\mathrm{ZnSb}$ as the only stable compound, crystallizing with the MnAlGe-type structure. From DFT calculations, an antiferromagnetic spin configuration of Cr local magnetic moments was found to be favorable for both the perfectly stoichiometric compound CrZnSb as well as for $\mathrm{C}{\mathrm{r}}_{0.875}\mathrm{ZnSb}$. Magnetic order is observed experimentally for $\mathrm{C}{\mathrm{r}}_{0.86}\mathrm{ZnSb}$ by temperature- and field-dependent magnetization measurements, revealing a magnetic phase transition near 220 K, which is corroborated by zero-field muon spin relaxation studies. Thermoelectric transport properties exhibit distinct maxima in the temperature-dependent Seebeck coefficient and electrical resistivity at around 190 K. Analyzing the measured data on the basis of a triple parabolic band model and DFT simulations, their characteristic features are traced back to a pseudogap in the electronic structure arising from a particular vacancy arrangement. These findings offer valuable insights into the role of vacancies in defect materials, contributing to the broader understanding of structural defects and their impact on the electronic structure.

The reflection point is different from the incident point on the interface between two Weyl semimetals, and a spatial shift happens during the reflection. The reflection shift vector as a function of in-plane wave vector shows vortex structures in the incident pocket (the projection of the isoenergy surface on the junction interface) and on the pocket edge. We propose a topological quantity, which is defined by the contour integration of reflection shift along the pocket edge and is proven to be the number of edge vortices as well as that of the interface Fermi arcs connected to the pocket. Every vortex is an interface particle loaded with unit topological charge and the distribution of these topological particles reflects the internal structure of the incident pocket under the influence of the transmitted medium.

Fano resonance is believed to arise when a direct path interferes with a resonant path. We demonstrate that this is not true for chiral electronic transmission without additional direct paths. To address the Fano effect in chiral electronic transport, we suggest an electronic Mach-Zehnder-Fano interferometer, which integrates a quantum dot into an electronic Mach-Zehnder interferometer. Due to the absence of backscattering in chiral electronic transport, Fano resonances can be fully adjusted by an external magnetic flux in the transmission, linear conductance, differential conductance, and differential shot noise of chiral electrons. Even the current and shot noise for a symmetric interferometer with two arms of the same length exhibit fully controllable resonances and distinct Fano characteristics. In particular, all the profiles in the various transport spectra follow the same evolution pattern in an evolution cycle that is resistant to changes in the device's defining parameters.

Janus transition metal-dichalcogenide materials have attracted a great deal of attention due to their remarkable physical properties arising from the two-dimensional geometry and the breakdown of the out-of-plane symmetry. Using first-principles density functional theory, we investigated the phase stability, strain-enhanced phase stability, and superconductivity of Janus WSeH and WSH. In addition, we investigated the contribution of the phonon linewidths from the phonon energy spectrum responsible for the superconductivity and the electron-phonon coupling as a function of phonon wave vectors and modes. Previous work has examined hexagonal 2H and tetragonal 1T structures, but we found that neither is a ground-state structure. The metastable 2H phase of WSeH is dynamically stable with ${\mathrm{T}}_c\approx 11.60\mathrm{K}$, similar to WSH. Compressive biaxial strain—the two-dimensional equivalent of pressure—can stabilize the 1T structures of WSeH and WSH with ${\mathrm{T}}_c\approx 9.23\mathrm{K}$ and 10.52 K, respectively.

Valley, as an emerging degree of freedom of electron, has attracted extensive attention on account of its huge potential in electronic component technology. Two-dimensional (2D) materials provide an ideal platform for the research of valleytronics. Here, we study the sliding and twist effects on valley of bilayer ${\mathrm{NiI}}_2$ by the first-principles calculations. For a monolayer, spatial inversion symmetry maintains the degeneracy of two valleys. In the AA stacking bilayer, which can be obtained by a vertical translation operation on a monolayer structure, the valley band splitting is absent due to the $\widehat{P}\widehat{T}$ joint symmetry. The interlayer sliding of the AA stacking bilayer can not break $\widehat{P}\widehat{T}$ joint symmetry and therefore there is not valley band splitting in a sliding system with respect to AA stacking. For the ${\mathrm{AA}}^{\prime }$ stacking bilayer, the valley band splitting occurs while the valley polarization is still absent as the $\widehat{M_Z}\widehat{T}$ joint symmetry. Different from the AA stacking system, $\widehat{M_Z}\widehat{T}$ joint symmetry of the ${\mathrm{AA}}^{\prime }$ system can be broken by interlayer sliding, and the valley polarization is realized. Furthermore, valley polarization is studied and it existed in twisted moiré structures with twist angles of $13.{174}^{\circ }$, $21.{787}^{\circ }$, $27.{796}^{\circ }$, $32.{204}^{\circ }$, ${38.213}^{\circ }$, and ${46.826}^{\circ }$, as the twisting breaks the spatial inversion symmetry. Our results broaden the valley polarization materials by interlayer sliding and twisting of 2D bilayer structures.

Motivated by exploring correlated multiorbital altermagnets ($\text{A}\ell \text{Ms}$) we study minimal $t-J$ models on the square-octagon lattice, which favors such a collinear magnetic order. While antiferromagnetic order breaks translational and time-reversal symmetries, the $\text{A}\ell \text{M}$ state (equivalently, a “$d$-wave ferromagnet”) features multipolar order, which separately breaks time-reversal and crystal rotation symmetries but preserves their product leading to spin-split bands with zero net magnetization. We study the mean-field phase diagram of these multiorbital models as we vary doping and interactions, discovering two types of $\text{A}\ell \text{M}$ order: (i) itinerant weak-coupling $\text{A}\ell \text{M}$ metals driven by quasi-1D van Hove singularities, as well as (ii) strong $\text{A}\ell \text{M}$ order at half-filling. We also find regimes of superconductivity including uniform $s$-wave and $d_{xy}$-wave pairing states, incipient $d_{xy}$-wave pair density wave order, and uniform phases with coexisting singlet-triplet pairing and $\text{A}\ell \text{M}$ order. Our inhomogeneous mean-field theory approach reveals that the coexistence phases are unstable to phase separation, but longer-range interactions could lead to stripe order. Our results may be relevant to studies of doping and pressure on $\text{A}\ell \text{M}$ materials.

The control of the spin degree of freedom is at the heart of spintronics, which can potentially be achieved by spin-orbit coupling or band topological effects. In this paper, we explore another potential controlled mechanism under debate: the spin-deformation coupling (SDC)—the coupling between intrinsic or extrinsic geometrical deformations and the spin degree of freedom. We focus on polar-deformed thin films or two-dimensional compounds, where the Rashba spin-orbit coupling (SOC) is considered as an $\text{SU}\left(2\right)$ non-Abelian gauge field. We demonstrate that the dynamics between surface and normal electronic degrees of freedom can be properly decoupled using the thin-layer approach by performing a suitable gauge transformation, as introduced in the context of many-body correlated systems. Our work leads to three significant results: (i) gauge invariance implies that the spin is uncoupled from the surface's extrinsic geometry, challenging the common consensus; (ii) the Rashba SOC on a curved surface can be included as an $\text{SU}\left(2\right)$ non-Abelian gauge field in curvilinear coordinates; and (iii) we identify a previously unnoticed scalar geometrical potential dependent on the Rashba SOC strength. This scalar potential, independent of spin, represents the residual effect remaining after decoupling the normal component of the non-Abelian gauge field. The outcomes of our paper open alternative pathways for exploring the manipulation of spin degrees of freedom through the use of the SDC.

We propose a nonlinear ac Hall effect in two-dimensional BCS single-band superconductors. Namely, a nonlinear ac transverse Hall current emerges in the superconductor interacting with an incident polarized light if a built-in dc supercurrent is present in the system. Applying the nonequilibrium Keldysh diagram technique, we calculate an ac Hall current density oscillating at double the electromagnetic field frequency. This current's strength is influenced by the inelastic relaxation rate, the dc supercurrent direction, and light polarization, with the ac current density being tunable via electron density. The ac Hall effect is unique to the superconducting state and is shaped by temperature, light frequency, and material characteristics.

In this study we revisit the properties of the $("8.88\times 8.88")\mathrm{R}{30}^{\circ }$ surface reconstruction obtained by evaporation of Cu on Ge(111), motivated by the predictions of Dirac nodal lines in two-dimensional ${\mathrm{Cu}}_2\mathrm{Ge}$ monolayer. After providing an updated version of the band structure of Ge(111) by angle-resolved photoemission (ARPES), we present the band structure of the $\mathrm{Cu}/\mathrm{Ge}\left(\mathrm{111}\right)\text{−}(8.88\times 8.88)\mathrm{R}{30}^{\circ }$ surface, which presents two surface bands, with having linear dispersion at the Fermi level.

We investigate the energy band structure and energy levels of graphene with staggered intrinsic spin-orbit coupling and in-plane Zeeman fields. Our study demonstrates that staggered intrinsic spin-orbit coupling induces bulk band crossover at the $K$ and $K^{\prime }$ valleys and generates antihelical edge states at the zigzag boundaries, resulting in topological metallic phases. Quantized transport coefficients confirm the existence of these antihelical edge states. Furthermore, an in-plane Zeeman field, regardless of orientation, opens a gap in the antihelical edge states while preserving bulk band closure, leading to higher-order topological metals with corner states. We also validate the presence of these corner states in nanoflakes with zigzag boundaries and confirm the metallic phases with crossed bands through a continuum low-energy model analysis.

We studied the absorption of microwave electromagnetic radiation incident normal to a two-dimensional electron system on a dielectric substrate with a metallic back reflector. We have shown that the presence of a back gate strongly modifies the spectrum of plasmon polaritons in such a structure. We observe a transverse plasmon mode which starts from zero frequency at zero magnetic field and follows renormalized cyclotron resonance. This renormalization occurs from the hybridization of plasma modes with Fabry-Pérot photonic resonances in the substrate, which indicates their transverse nature. Finally, we speculate that the observed modes resemble helicon waves in three-dimensional metals.

The advances of machine-learned force fields have opened up molecular dynamics (MD) simulations for compounds for which ab initio MD is too resource intensive and phenomena for which classical force fields are insufficient. Here we describe a neural-network force field parametrized to reproduce the ${\mathrm{r}}^2\mathrm{SCAN}$ potential energy landscape of ${\mathrm{HfO}}_2$. Based on an automatic differentiable implementation of the isothermal-isobaric $\left(NPT\right)$ ensemble with flexible cell fluctuations, we study the phase space of ${\mathrm{HfO}}_2$. We find excellent predictive capabilities regarding the lattice constants and experimental x-ray diffraction data. The phase transition away from monoclinic is clearly visible at a temperature around 2000 K, in agreement with available experimental data and previous calculations. Another abrupt change in lattice constants occurs around 3000 K. While the resulting lattice constants are closer to cubic, they exhibit a small tetragonal distortion, and there is no associated change in volume. We show that this high-temperature structure is in agreement with the available high-temperature diffraction data.

The conductive properties and defect structure of Sn-doped $\beta \text{−}{\mathrm{Ga}}_2{\mathrm{O}}_3$ bulk materials with different Sn concentrations are studied in this work. The calculations and experiments of positron annihilation spectroscopy clarify the existence of Ga monovacancies of high concentrations in these semiconductors. The temperature dependencies of positron annihilation parameters and the linear relationship between compensating carrier concentration and Ga vacancy concentration clearly reveal that the $-3$ charged Ga monovacancies are the dominant intrinsic acceptors in Sn-doped $\beta \text{−}{\mathrm{Ga}}_2{\mathrm{O}}_3$.

We present the microscopic theory of the spin Nernst effect, which is a transverse spin current directly induced by a temperature gradient, employing the linear response theory with Luttinger's gravitational potential method. We consider a generic, noninteracting electron system with randomly distributed impurities and evaluate the spin current response to the gravitational potential. Our theory takes into account a contribution of the local equilibrium current modified by Luttinger's gravitational potential and is thus consistent with the thermodynamic principle that thermal responses should vanish at absolute zero. The Ward-Takahashi identities ensure that the spin Nernst current is well-behaved at low temperatures in any order of the random impurity potentials. Furthermore, we microscopically derive the spin-current version of Mott's formula, which associates the spin Nernst coefficient with the spin Hall conductivity. The spin-current version of the Středa formula is also discussed. To demonstrate these findings, the spin Nernst current of three-dimensional Dirac electrons is computed. Our theory is general and can therefore be extended to interacting electron systems, where Mott's formula no longer holds.