Kagome superconductors $A{\text{V}}_3{\text{Sb}}_5$ ($A=$ K, Rb, Cs) exhibit a characteristic superconducting and charge-density wave (CDW) phase diagram upon carrier doping and chemical substitution. However, the key electronic states responsible for such a phase diagram have yet to be clarified. Here we report a systematic microfocused angle-resolved photoemission spectroscopy study of ${\text{Cs(V}}_{1-x}{\text{Cr}}_x{)}_3{\text{Sb}}_5$ as a function of Cr content $x$, where Cr substitution causes monotonic reduction of superconducting and CDW transition temperatures. We found that the V-derived bands forming saddle points at the M point and Dirac nodes along high-symmetry cuts show an energy shift due to electron doping by Cr substitution, whereas the Sb-derived electron band at the $\mathrm{\Gamma }$ point remains almost unchanged, signifying an orbital-selective band shift. We also found that band doubling associated with the emergence of three-dimensional CDW identified at $x=0$ vanishes at $x\ge 0.25$, in line with the disappearance of CDW. A comparison of band diagrams among Ti-, Nb-, and Cr-substituted $\text{Cs}{\text{V}}_3{\text{Sb}}_5$ suggests the importance to simultaneously take into account the two saddle points at the M point and their proximity to the Fermi energy, to understand the complex phase diagram against carrier doping and chemical pressure.

A nonlinear Hall effect (NHE) can originate from the quantum metric mechanism in antiferromagnetic topological materials with $PT$ symmetry, which has been experimentally observed in ${\mathrm{MnBi}}_2{\mathrm{Te}}_4$. In this paper, we propose that breaking $PT$ symmetry via external electric fields can lead to a dramatic enhancement of NHE, thus allowing for an electric control of NHE. Microscopically, this is because breaking $PT$ symmetry can lift the spin degeneracy of a Kramers pair, giving rise to additional contributions within one Kramers pair of bands. We demonstrate this enhancement through a model Hamiltonian that describes an antiferromagnetic topological insulator sandwich structure.

We report on a resonant inelastic x-ray scattering study on a single crystal of a nonstoichiometric pyrochlore iridate ${\mathrm{Tb}}_{2+x}{\mathrm{Ir}}_{2-x}{\mathrm{O}}_{7-y}$ ($x\simeq 0.25$) that magnetically orders at $T_{\mathrm{N}}\simeq 50$ K. We observe a propagating gapped magnon mode at low energy and model it using a Hamiltonian consisting of a Heisenberg exchange $[J=16.2(9\left)\mathrm{meV}\right]$ and Dzyaloshinskii-Moriya interactions $[D=5.2(3\left)\mathrm{meV}\right]$, which shows the robustness of interactions despite Tb stuffing at the Ir site. Strikingly, the ratio $D/J=0.32\left(3\right)$ supports possible nontrivial topological magnon band crossing. This material may thus host coexisting fermionic and bosonic topology, with potential for manipulating electronic and magnonic topological bands thanks to the $d\text{−}f$ interaction.

The effects of 2.5-MeV electron irradiation on the magnetic properties of single crystals of the Remeika series superconductor ${\text{Ca}}_3{\text{Rh}}_4{\text{Sn}}_{13}$ were studied using high-frequency ac susceptometry, magnetization, and electrical transport. This low-pinning cubic stannide is an ideal system to examine the effects of a controlled nonmagnetic pointlike disorder. The measured Campbell penetration depth was used to extract the magnetic field dependence of the unrelaxed critical current density, $j_c\left(H\right)$. The critical current is a monotonic function of a magnetic field in pristine state. However, even the lowest dose of electron irradiation causes a pronounced peak effect in $j_c\left(H\right)$. The peak effect is also observed in magnetization measurements performed with different characteristic time windows. We conclude that additional defects trigger the appearance of a disordered vortex phase at magnetic fields close to the upper critical field, and the peak effect is the result of a crossover from the weakly distorted low-field vortex lattice to the disordered high-field vortex phase. These results strongly support the static picture of the peak effect formation in ${\mathrm{Ca}}_3{\mathrm{Rh}}_4{\mathrm{Sn}}_{13}$ in which this is a feature of the critical current density, $j_c\left(H\right)$, and not the result of magnetic field-dependent vortex relaxation, $j(H,t)$.

We use ab initio electromagnetic simulations to investigate light absorption by rough surfaces in the context of the formation of laser-induced periodic surface structures. Our approach involves modeling a rough surface using a statistical description of its continuous height distribution via a corresponding correlation function. We study the influence of incident light polarization and various statistical properties of surface roughness, such as root-mean-square height and correlation length, on the distribution of absorbed laser energy. By analyzing light absorption in different layers of the surface selvedge, we elucidate how different features of surface morphology influence the shape of the resulting periodic surface structures. We show that circularly polarized laser pulses are highly sensitive to initial or progressively developing asymmetries in surface roughness.

Half-metallicity is very important in spintronics due to its ability to realize fully spin polarized transport. Due to the rise of two-dimensional (2D) materials, how to achieve half-metallicity in 2D materials has attracted great attention in recent years and various schemes have been proposed for this goal in intrinsically non-half-metallic magnetic systems, whereas these schemes are primarily limited to antiferromagnetic systems. It is desirable and significant to turn ferromagnets into half-metals. In this work, by taking magnetic ${\mathrm{LaBr}}_2$ monolayer as an example, based on density functional theory calculations, we propose a scheme to achieve half-metallicity in a kind of ferromagnetic systems called spin semiconductors by forming a van der Waals (vdW) heterostructure with a 2D ferroelectric material $\alpha \text{−}{\mathrm{In}}_2{\mathrm{Se}}_3$. It is found that not only half-metallicity can be achieved in ${\mathrm{LaBr}}_2$, but it can also switch between half-metal and semiconductor accompanying with ferroelectric polarization reversal under the external electric field. The switching is interpreted by the interlayer charge transfer due to the appropriate work function differences between the contacted two surfaces. Further the obtained extremely high spin polarization (99.94%), tunnel electroresistance ratio ($2.11\times {10}^5\%$), and tunnel magnetoresistance ratio ($1.62\times {10}^4\%$) in the subsequent transport study of the multiferroic tunnel junction constructed with ${\mathrm{LaBr}}_2/\alpha \text{−}{\mathrm{In}}_2{\mathrm{Se}}_3$ vdW heterostructure demonstrates that this provides a novel scheme for the new multifunctional applications of spin semiconductors such as ${\mathrm{LaBr}}_2$, either as a spin filter generator, or as a building block of data storage units based on giant tunnel electroresistance effect or giant tunnel magnetoresistance effect.

Using unbiased Monte Carlo simulations and variational analysis, we present the ground state and finite-temperature phase diagrams of an exactly solvable spin-orbital model with Kitaev-type interactions on a square lattice. We show that an array of gapped and gapless vison crystals, characterized by the periodic arrangement of ${\mathbb{Z}}_2$ flux excitations, can be stabilized as a function of external magnetic field and exchange anisotropy. In particular, we discover a variety of “quarter phases” wherein different 16-site periodic patterns emerge, with only a quarter of the fluxes adopting zero-flux configurations. In contrast, the rest remain in $\pi$-flux configurations. Vison crystals break translational symmetry and undergo finite-temperature phase transitions. We investigate the finite-temperature properties of these phases and report the corresponding critical and crossover temperatures. Our results reveal an array of novel phases in exactly solvable extensions of the Kitaev model, wherein local and topological orders can coexist.

The recent discovery of superconductivity in the bilayer nickelate ${\mathrm{La}}_3{\mathrm{Ni}}_2{\mathrm{O}}_7$ under high pressure has garnered significant interest due to its high transition temperature surpassing the liquid nitrogen limit. This breakthrough has prompted an extensive amount of research aimed at identifying new superconducting nickelates and elucidating the underlying mechanism responsible for superconductivity in ${\mathrm{La}}_3{\mathrm{Ni}}_2{\mathrm{O}}_7$. Here we report our findings on the effect of Nd doping in ${\mathrm{La}}_3{\mathrm{Ni}}_2{\mathrm{O}}_7$. Electrical transport measurements conducted at ambient pressure reveal that as the Nd doping concentration increases, ${\mathrm{La}}_{3-x}{\mathrm{Nd}}_x{\mathrm{Ni}}_2{\mathrm{O}}_7$ (with $x=0$, 0.3, 0.6, 0.9) samples transition from a bad metal to a semiconductor. However, the density wave transition temperature remains unaffected across all ${\mathrm{La}}_{3-x}{\mathrm{Nd}}_x{\mathrm{Ni}}_2{\mathrm{O}}_7$ samples. Magnetic property investigations indicate that all doped samples exhibit paramagnetic behavior. Furthermore, we performed resistance measurements under high pressure on the undoped and doped samples. All the samples show a signature of superconductivity at about 80 K under pressure. Our observations extend the scope of doping studies in ${\mathrm{La}}_3{\mathrm{Ni}}_2{\mathrm{O}}_7$, which will aid in the exploration of the superconducting mechanism within this promising nickelate compound.

We show that spin-singlet $s$-wave multiband superconductors have a topological phase protected by rotation symmetry and time-reversal symmetry without spin-orbit coupling in two and three dimensions. This topological phase, an example of a representation-protected topological phase, has a ${\mathbb{Z}}_2$ topological index and is stable as long as the bands at the Fermi energy are formed by a doublet of orbital states with finite angular momenta. In the limit of weak superconducting pair potential, the ${\mathbb{Z}}_2$ index gives a Fermi-surface formula and is related to the winding number of three-dimensional strong topological superconductors of class CI. We present a model of a topological $s_{\pm }$-wave superconductor that has gapless surface states with a quadratic dispersion and suggest a connection with iron-based superconductors.

Symmetries govern macroscopic physical quantities, and the electronic and spin properties of crystals. Here, we demonstrate that the spin-orbit-induced spin polarization at the Brillouin zone border for noncentrosymmetric and nonsymmorphic space groups is dictated by the wave function symmetries instead of, as commonly held, the point group symmetry of a wave vector. This is confirmed and exemplified by a group-theoretical analysis and density-functional theory calculations on several space groups and realistic materials. Our results are expected to enrich the fundamental understanding of symmetry-dictated spin-orbit physics and broaden the range of spintronic materials.

Lindbladian dissipative processes can be determined by stochastic samplings of individual trajectories, whose non-Hermitian evolution is perturbed by quantum jumps. The conditional dynamics of the jump events is fundamental to access many relevant statistical quantities of the dissipative dynamics. In this work, we mostly focus on the conditional no-jump evolution of noninteracting chains, including partial missed detection of jumps. As a main result, for Gaussian-preserving Lindblad operators, the conditional dynamics is captured by a nonlinear Riccati-type differential equation for the correlation matrix. As an application, we study the no-jump probability and the waiting-time distributions for chains of hopping particles and double quantum dots.

We present a density functional theory based study of a two-dimensional ferromagnetic Janus $\mathrm{V}XY$ $(X=\mathrm{Cl}, \mathrm{Br}, \mathrm{I}; Y=\mathrm{S}, \mathrm{Se}, \mathrm{Te})$ structure. The dynamical and thermal stabilities of all possible $\mathrm{V}XY$ structures consisting of chalcogen and halogen atoms in the $1T$ and $2H$ phases are determined. Among them, only the $1T$ phases of the VBrS, VIS, and VISe structures are found to be stable. These structures show semiconducting properties and demonstrate spin-orbit-induced valley splittings, reaching 0.1 eV in the VISe monolayer. These structures exhibit in-plane easy axes with Curie temperatures around $\sim 100\mathrm{K}$ estimated based on the classical Monte Carlo and quantum Green's function techniques. On the other hand, the absence of inversion symmetry in Janus $\mathrm{V}XY$ compounds gives rise to the Dzyaloshinskii-Moriya interaction with the possibility of forming chiral magnetic structures. In the absence of an external magnetic field, Janus $\mathrm{V}XY$ monolayers exhibit magnetic chiral structures at 0 K, evidenced by nonzero $Q$ (topological charge) values from Monte Carlo simulations. By applying an out-of-plane magnetic field of around 0.7 T, we observe the formation of skyrmions. At 5 K, the VIS monolayer demonstrates chiral magnetic structures, while VBrS and VISe display Néel-type domain walls. VISe forms a skyrmion lattice at $\sim 0.1\mathrm{T}$ which does not persist beyond this value. Since all the structures have an in-plane easy axis, an in-plane magnetic field of around 0.5 T at 0 K gives rise to the formation of bimerons.

Understanding, manipulating, and using magnons—the quanta of spin waves—for energy-efficient applications is one of the primary goals of magnonics. In this paper, we consider a synthetic antiferromagnet in which one of the ferromagnetic layers is driven by spin-orbit torque. We find that under specific conditions for the magnitude of the spin-orbit torque and field, magnon pairs are spontaneously produced by quantum fluctuations in a way that is similar to Hawking pair production near black-hole horizons. One of the magnons is generated near the interface with the spacer layer in one of the magnetic layers of the synthetic antiferromagnet, while the other magnon is produced in the other magnetic layer. We compute the magnon current due to these spontaneously generated magnon pairs and estimate the temperature below which they should become observable. Additionally, we find that the magnons are entangled, which makes them interesting for future applications in quantum magnonics.

Magnetic skyrmions and antiskyrmions are characterized by an integer topological charge $\mathcal{Q}=\mp 1$, describing the winding of the magnetic orientation. Half-integer winding numbers, $\mathcal{Q}=\pm \frac{1}{2}$, can be obtained for magnetic vortices (merons). Here, we discuss the physics of magnets with fractional topological charge which is neither integer nor half-integer. We argue that in ferromagnetic films with cubic anisotropy, textures with $\mathcal{Q}=\pm \frac{1}{6}$ or $\pm \frac{1}{8}$ arise naturally when three or more magnetic domains meet. We also show that a single magnetic skyrmion with $\mathcal{Q}=-1$ can explode into four fractional defects, each carrying charge $\mathcal{Q}=-\frac{1}{4}$. Additionally, we investigate a point defect with a nonquantized fractional charge ($\mathcal{Q}\ne \frac{n}{m},n,m\in \mathbb{Z}$) which can move parallel to a magnetic domain wall. Only defects with fractional charge lead to an Aharonov-Bohm effect for magnons. We investigate the resulting forces on a fractional defect due to magnon currents.

Quasi-one-dimensional Cr-based superconductor ${\mathrm{K}}_2{\mathrm{Cr}}_3{\mathrm{As}}_3$ has aroused great research interest due to its possible triplet pairing symmetry. Recent experiments have shown that incorporating hydrogen into ${\mathrm{K}}_2{\mathrm{Cr}}_3{\mathrm{As}}_3$ would significantly change its electronic and magnetic properties. Hence, it is necessary to investigate the impact of hydrogen doping in the pairing symmetry of this material. Employing the hydrogen as a nontrivial electron doping, our calculations show that the system exhibits $p_x\pm i{p}_y$-wave pairing symmetry under specific hydrogen doping, in contrast with the $p_z$-wave one obtained without hydrogen. Specifically, we adopt the random-phase-approximation approach based on a six-band tight-binding model equipped with multiorbital Hubbard interactions to study the hydrogen doping dependence of the pairing symmetry and superconducting $T_c$. Under the rigid-band approximation, our pairing phase diagram shows that the spin-triplet pairing covers the hydrogen doping regime $x\in (0,0.7)$. In particular, the $T_c\sim x$ curve shows a peak at the 3D-quasi-1D Lifshitz transition point, and the pairing symmetry near this doping level is $p_x\pm i{p}_y$. The physical origin of this pairing symmetry is that the density of states is mainly contributed from momenta with large $k_x\left(k_y\right)$ components on the Fermi surface. Due to the three-dimensional characteristic of the real material, this $p_x\pm i{p}_y$-wave pairing possesses a point-node gap. We further provide experiment predictions to identify this triplet $p_x\pm i{p}_y$-wave superconductivity.

The transport experiments demonstrate a dramatic switch from the low-temperature linear in temperature ($T$-linear) resistivity in the overdoped strange-metal phase of cuprate superconductors to the low-temperature quadratic in temperature ($T$-quadratic) resistivity in the underdoped pseudogap phase; however, a consensus on the origin of this unusual switch is still lacking. Here the resistivity in the underdoped pseudogap phase of cuprate superconductors is investigated using the Boltzmann transport equation. The resistivity originates from the electron umklapp scattering mediated by the spin excitation; however, the dominant contribution mainly comes from the antinodal umklapp scattering. In particular, a low-temperature $T_{\mathrm{scale}}$ scales with ${\mathrm{\Delta }}_p^2$ in the underdoped regime due to the opening of a momentum-dependent spin pseudogap, where ${\mathrm{\Delta }}_p$ is the minimal umklapp vector at the antinode. Moreover, this $T_{\mathrm{scale}}$ decreases with the increase of doping in the underdoped regime, and then is reduced to a very low temperature in the overdoped regime. In the underdoped regime, the resistivity is $T$-quadratic at the low temperatures below $T_{\mathrm{scale}}$, where the strength of the $T$-quadratic resistivity weakens as the doping is raised. However, in the overdoped regime, the resistivity is $T$-linear at the low temperatures above $T_{\mathrm{scale}}$. The results in this paper together with the recent study on the resistivity in the overdoped regime therefore show that the electron umklapp scattering from a spin excitation responsible for the low-temperature $T$-linear resistivity in the overdoped regime naturally produces the low-temperature $T$-quadratic resistivity in the underdoped regime resulting from the opening of a momentum-dependent spin pseudogap.

In this study, we aim to understand the atomic structure of uranium-incorporated sodium borosilicate glasses, with implications for a long-term storage of high-level nuclear waste. We simulated a series of glasses with a general composition of $70\text{wt.}\%[{\left({\text{SiO}}_2\right)}_{65-x}·{\left({\text{B}}_2{\text{O}}_3\right)}_x·{\left({\text{Na}}_2\text{O}\right)}_{25}·{\left({\text{ZrO}}_2\right)}_5·{\left(\text{BaO}\right)}_5]+30\text{wt.}\%{\text{UO}}_3$, where $x=5, 10, 15, 20$ mol%. We adopted force-enhanced atomic refinement (FEAR) and melt-quench (MQ) methods to simulate these glasses in cubic supercells consisting of 340–365 atoms. The structure factors obtained from the FEAR models reveal good agreement with diffraction experiments and closely match to those of the MQ models. We quantified the structural topologies of the glasses within local order using higher-order correlation functions such as partial pair distribution functions, bond-angle distribution functions, and coordination numbers. The splitting of uranium-oxygen correlations in the first coordination sphere is observed, and we discuss the structural origins of such splitting, along with the network connectivity of uranium in the glasses. We analyzed the effect of ${\mathrm{SiO}}_2/{\mathrm{B}}_2{\mathrm{O}}_3$ substitution on glass-network connectivity by quantifying bridging and nonbridging oxygen atoms, and $Q_n$ distributions. In addition, we investigated the vibrational and electronic properties of the MQ models with $x=10\%$ and 20%. The vibrational signatures of the studied glasses are found to be similar to those of ${\mathrm{Na}}_2\mathrm{O}\text{−}{\mathrm{SiO}}_2\text{−}{\mathrm{B}}_2{\mathrm{O}}_3$ glasses. The electronic density of states near the valence and conduction edges are primarily attributed to oxygen and uranium orbitals, respectively, and the electronic eigenstates in those edges are highly localized.

This paper reports an investigation of the pressure dependence of lattice-dynamical and dielectric properties of ${\mathrm{CuAlO}}_2$ delafossite by means of Fourier transform infrared spectroscopy and ab initio calculations. The availability of single-crystal and powdered samples allowed for an almost complete characterization of the pressure behavior of polar phonons and dielectric function from the far-infrared to the near-ultraviolet spectral range. The pressure-induced increase of the electronic contribution to the dielectric constant for polarization perpendicular to the $c$ axis is fully accounted for by volume reduction, showing that the electronic polarizability remains virtually constant under pressure. The behavior of the polar phonon contribution to the static dielectric constant is more complex. The contribution of the high-frequency $E_{u,\mathrm{TO}}^h$ mode $(489 \mathrm{c}{\mathrm{m}}^{-1})$, with positive pressure coefficient, slightly decreases under pressure. On the opposite, the contribution of the low-frequency $E_{u,\mathrm{TO}}^l$ mode (143 $\mathrm{c}{\mathrm{m}}^{-1}$ at ambient pressure) largely increases as it becomes softer under pressure, leading to an overall increase of the static dielectric constant. For polarization parallel to the $c$ axis, the electronic contribution is insensitive to pressure. The polar mode $A_{2u,\mathrm{TO}}^h$ (700 $\mathrm{c}{\mathrm{m}}^{-1}$) has positive pressure coefficient. Then, an overall decrease of the static dielectric constant for polarization parallel to the $c$ axis is expected.