Rapid development of material systems containing lanthanides (Ln) highlights the need for a thorough evaluation of Ln-driven properties, for which Ln-sensitive resonant photoelectron spectroscopy (RPES) can be particularly useful. Employing RPES in combination with theoretical modeling, we investigate in detail the ${\mathrm{LnRh}}_2{\mathrm{Si}}_2$ compound family, particularly to examine how photoelectron diffraction (PED) and the crystal electric field (CEF) influence the resonantly enhanced $4f$ emission associated with individual $|M_J\rangle$ ground states. The presence of two well-defined Ln- and Si-terminated surfaces together with the pronounced reorientation of $4f$ moments at the surface due to change of CEF makes ${\mathrm{LnRh}}_2{\mathrm{Si}}_2$ particularly well suited for this study, which was performed for the region of Ln $4d\stackrel{}{\to }4f$ excitations. High-quality data for Tb, Tm, and Ho enabled detailed analysis of the effects of PED and CEF on the RPES $4f$ spectra for individual $|M_J\rangle$ states, revealing excellent agreement between experiment and theory. Based on this, we discuss theoretical results for other ${\mathrm{LnRh}}_2{\mathrm{Si}}_2$ systems. The resulting overview of resonant $4f$ photoemission spectra and PED patterns provides a solid platform for investigating a wide range of Ln-based systems, from molecules to solids, with a particular focus on evaluating properties arising from $4f$ magnetic moments and their orientation.

We conducted time-dependent density functional theory simulations to investigate the neutralization process of a hydrogen ion injected at 100 eV onto the (110) surface of tungsten. Additionally, we introduced a method for evaluating the detection probability of electrons within a localized region. This probability serves as an indicator for identifying hydrogen in its various states: positive ion, neutral atom, and negative ion. Our findings indicate that following the collision, the probabilities of detecting hydrogen as a positive ion, neutral atom, and negative ion are approximately 25%, 50%, and 25%, respectively.

We report our investigations on ${\mathrm{Ag}}_3{\mathrm{LiIr}}_{1.4}{\mathrm{Ru}}_{0.6}{\mathrm{O}}_6$, which results from the Ru substitution in the Kitaev quantum spin-liquid candidate ${\mathrm{Ag}}_3{\mathrm{LiIr}}_2{\mathrm{O}}_6$. It crystallizes in the monoclinic $C2/m$ space group like its parent compound, ${\mathrm{Ag}}_3{\mathrm{LiIr}}_2{\mathrm{O}}_6$. Our susceptibility measurements reveal an effective moment ${\mu }_{\text{eff}}=2.6{\mu }_B$, which is higher than moments of the parent compound and less than that of the Ru analog $\left({\mathrm{Ag}}_3{\mathrm{LiRu}}_2{\mathrm{O}}_6\right)$, suggesting the presence of magnetic ${\mathrm{Ir}}^{4+}$ $(J_{\text{eff}}=1/2)$ and ${\mathrm{Ru}}^{4+}$ $(S=1)$. Bulk magnetic susceptibility suggests long-range order (LRO) at $T\sim 20\mathrm{K}$, whereas no clear signature is present in the heat capacity. Likewise, there is a loss of the ${}^7\mathrm{Li}$ nuclear magnetic resonance (NMR) spectral intensity around $T\sim 20\mathrm{K}$ as expected at the onset of LRO but a complete wipeout is not seen, in contrast to the result in ${\mathrm{Ag}}_3{\mathrm{LiIr}}_2{\mathrm{O}}_6$. There is as well a $T\sim 20\mathrm{K}$ anomaly in the ${}^7\mathrm{Li}$ NMR relaxation rate $1/T_1$ and also a fall in the ${}^7\mathrm{Li}$ NMR shift $K$ with decreasing temperature. These results suggest LRO at $T\sim 20\mathrm{K}$ in ${\mathrm{Ag}}_3{\mathrm{LiIr}}_{1.4}{\mathrm{Ru}}_{0.6}{\mathrm{O}}_6$. However, at low $T$ below 10 K, we observe a power-law variation in magnetic heat capacity $C_m$ and spin-lattice relaxation rate $1/T_1$, temperature-independent ${}^7\mathrm{K}$, temperature-independent muon spin relaxation rate, and no further loss of the ${}^7\mathrm{Li}$ NMR spectral intensity. These results suggest the persistence or stabilization of a quantum spin-liquid-like phase perhaps from a fraction of the sample in ${\mathrm{Ag}}_3{\mathrm{LiIr}}_{1.4}{\mathrm{Ru}}_{0.6}{\mathrm{O}}_6$ below 10 K. Our muon spin relaxation $\left(\mu \mathrm{SR}\right)$ measurements suggest ordering around 20 K, consistent with our other probes. It appears that the main effect of Ru substitution is to shift the LRO to a higher temperature in comparison with ${\mathrm{Ag}}_3{\mathrm{LiIr}}_2{\mathrm{O}}_6$, though there are signatures of a novel phase below about 10 K.

The study of the interplay between the geometric nature of Bloch electrons and transverse responses under a strong field offers new opportunities for optoelectronic applications. Robust nonlinear anomalous Hall phenomena can originate in inversion asymmetric crystals with avoided band crossings due to large Berry curvature peaks. Here, we investigated the relationship between nonlinear Hall effects and nonlinear optical responses of bilayer ${\mathrm{WTe}}_2$, ranging from perturbative to nonperturbative regimes. The high-harmonic generation (HHG) spectra under a strong field clearly exhibit a plateau and energy cutoffs, i.e., an unambiguous signature of nonperturbativeness, for both longitudinal and anomalous Hall (transverse) currents, with the latter being due to the large interband Berry curvature. For the longitudinal harmonics, the intraband contributions increase with intensity, resulting in a complex interplay between interband polarization and intraband motions. If we take a comprehensive all-band perspective enabled by time-dependent density functional calculations and define the intraband current as the diagonal part of the total current density matrix obtained through the projection operation, the anomalous Hall responses are attributed to the interband processes, even in the nonperturbative regime, though the decomposition into the intra- and interband components is arbitrary rather than physically essential. Thus, Hall HHG can be crucial to understand the carrier dynamics. Our findings suggest that HHG associated with the ultrafast strong-field-driven electron dynamics holds immense potential for exploring the nonlinear high Hall responses in noncentrosymmetric semimetals.

We investigate the anisotropic effect of magnetization plateaus in the antiferromagnetic Heisenberg model on a kagome strip chain. The kagome strip chain Heisenberg model, composed of a hexagonal net of triangles forming five-site unit cells, exhibits four magnetization plateaus in the presence of an applied magnetic field. Using numerical density matrix renormalization group method, we find that the magnetization plateaus are stable against anisotropic interactions in the same direction of the applied magnetic field, but the plateaus become much smaller with anisotropic interactions in other directions. We further show the anisotropic effect of the magnon excitations of the 0.6 plateau state using linear spin wave theory. The magnon bandwidth remains small when tuning the anisotropic interactions along the field where the magnetization plateau is stable, while the band becomes more dispersive with anisotropic interactions perpendicular to the field. In addition, upon tuning down the interaction strength for the two lower legs below a critical value, the Hamiltonian of the kagome strip chain is dominated by two separate spin chains. This can be used to determine the effective lattice structure in materials with strong distortions. Our results enhance the theoretical understanding of the anisotropic effect and the nature of magnetization plateaus in kagome strip chain materials, which can contribute to the design and manipulation of kagome materials with tailored properties.

The three-dimensional (3D) Fermi surface, along with a chiral in-gap state and a Majorana zero-energy state, is suggested to play a crucial role in the topologically nontrivial superconductivity in ${\mathrm{UTe}}_2$. However, conflicting experimental observations of the two-dimensional (2D) Fermi surface raise questions about topological superconductivity. By combining ab initio many-body perturbation GW theory and dynamical mean field theory based on Feynman diagrams, we discovered the coexistence of two orbital dependent Fermi surfaces, both centered at the $\mathrm{\Gamma }$ point in the Brillouin zone, which are heavily influenced by the orbital selective Kondo effect. At high temperature, both Fermi surfaces exhibit 3D nature with weak spectral weight due to incoherent Kondo hybridization. Upon cooling down to 25 K, due to the pronounced Kondo coherence, while one Fermi surface remains a robust 3D Fermi surface, the other transforms surprisingly into a quasi-2D Fermi surface, which should be responsible for the experimental observation of 2D character. Our results suggest that the 3D Fermi surface should exist at low temperature for the topological superconductivity. Our findings call for further investigation of the interplay between the two orbital-dependent $\mathrm{\Gamma }$-centered Fermi surfaces.

The intrinsic magnetic topological material ${\mathrm{MnBi}}_2{\mathrm{Te}}_4$ has demonstrated great potential to investigate the interplay between topology and magnetism, which opens up new avenues for manipulating nontrivial electronic states and designing quantum devices. However, challenges and controversies remain due to its inevitable $n$-type antisite defects, hindering the experimental realization of intrinsic magnetic topological phenomena and rendering the precise control of topological phase transitions (TPTs) unachievable. Here, we study a candidate material family, ${\mathrm{Mn}}_{(1-x)}{\mathrm{Ge}}_x{\mathrm{Bi}}_2{\mathrm{Te}}_4$, in which the heavy $n$-type doping features are strongly suppressed when the Ge content reaches 0.46, and multiple topological phases are well maintained with the surface Dirac point located near the Fermi level. Based on angle-resolved photoemission spectroscopy, transport measurements, and first-principles calculations, we reveal two magnetism-induced TPTs: the first is an antiferromagnetic-ordering-induced transition from strong topological insulator to a magnetic topological insulator as revealed by gap opening of topological surface states; the second is the external-magnetic-field-dependent transition from magnetic topological insulator to a Weyl semimetal with the gap reclosed. Our work paves the way for the realization of intrinsic magnetic topological states in the ${\mathrm{MnBi}}_2{\mathrm{Te}}_4$ family and provides an ideal platform for achieving controllable and continuous TPTs toward future spintronic applications.

A slow wave, which has a long period and low propagation speed, is widely utilized in the transmission and modulation of signals in high-frequency communication devices. Recently, with the development of topological theory, topologically protected slow-wave modulation has been successful in photonic crystals. However, due to the complicated fluid-structure interaction in the underwater environment, the realization of an acoustic broadband slow wave is still a challenge. In this paper, we construct a spin-Chern acoustic topological insulator with helical edge states, consisting of a water-filled connected-cavities rigid structure with a bilayer kagome lattice. The exhibited continuous and gapless helical edge dispersion originates from artificial time-reversal symmetry, which is engineered via next-nearest-neighbor chiral intercell interlayer coupling. Through introducing extra adjustable cavity coupling with helical edge states, the dispersion winds many times around the Brillouin zone to be nearly flat. Consequently, the slow-wave effect is perfectly presented in a wide frequency range. Our structure is protected by both time-reversal symmetry and spatial-inversion symmetry, providing an approach for underwater acoustic transmission and the design of industrial delay devices.

Altermagnetic (ATM) skyrmions embody a macroscopic realization of microscopic $d$-wave symmetry, as revealed by their unique spin textures in materials. Through lattice rotational symmetry and spin ordering, ATMs show exchange-driven spin splitting with directional dependence, imprinting $d$-wave anisotropy—modulated by the exchange difference $J_1-J_2$—onto skyrmion configurations. Our analysis, combining simulations and theoretical modeling, uncovers a ${90}^{\circ }$ interlayer orientation between elliptical skyrmion pairs, a geometric hallmark validated by $C_4$ symmetry and anisotropic Berry curvature. We propose this angle as a rotational invariant, underscoring ATM skyrmions' potential as topological probes for spintronics and beyond.

Two-dimensional (2D) materials hosting antiferromagnetic skyrmions are promising candidates for next-generation small-scale skyrmionic storage devices. However, the realization of antiferromagnetic skyrmions in intrinsic 2D materials, particularly in the widely studied $M{A}_2$-like ($M$ = transition metals; $A$ = chalcogen or halogen elements) materials, remains elusive. Here, we theoretically demonstrate the emergence and strain modulation of 2D antiferromagnetic skyrmion crystal (AF-SkX) in Janus V-based dihalides $\mathrm{V}\mathit{XY} (X,Y=\text{Cl,}\text{Br,}\text{I};X\ne Y)$. The interplay between antiferromagnetic exchange and Dzyaloshinskii-Moriya interaction (DMI) gives rise to the AF-SkX phase in $\mathrm{V}X\mathrm{I}$, which consists of three antiferromagnetically coupled skyrmion crystals. Furthermore, tensile strain significantly reduces the effective magnetic field strength required to realize AF-SkX and broadens the field range over which AF-SkX appears, increasing both the feasibility and stability of AF-SkX in VClI. Our findings expand the family of 2D materials capable of hosting AF-SkX and provide perspectives for engineering antiferromagnetic skyrmions in 2D materials.

We consider a simple cubic lattice with a ${\mathrm{Eu}}^{2+}$ ion at each corner and spins aligned parallel or antiparallel to the $z$ axis, depending on the long-range order phase of the ground state. Elementary excited states consist of transitions ${\mathrm{Eu}}^{2+}\left(4f^7\right)$ to ${\mathrm{Eu}}^{3+}\left(4f^6\right)5d$ at one site which give rise to the $5d$ conduction electron band structure. To prevent double occupation of the $5d$ states we introduce auxiliary bosons and fermions in mean-field approximation. For small $5d$ electron density $x$ we calculate the ground-state energies for the A, B, C, and G phases as a function of the nearest-neighbor hopping matrix element $t$ and the antiferromagnetic superexchange between neighboring spins $J^{*}$. With increasing superexchange there are crossovers from phase A to C and for large $J^{*}$ to G, while the B phase is only the ground state for ferromagnetic exchange. We study the canting of the spins which may lower the energy for the A and C phases. Following a procedure by M. Yu. Kagan et al. [J. Phys.: Condens. Matter 8, 10905 (2006)]. we investigate the formation of magnetic polarons as a function of anisotropy, magnetic field, and temperature, as well as the magnetostriction. This simplified model was inspired on the recently discovered Zintl compound ${\mathrm{Eu}}_5{\mathrm{In}}_2{\mathrm{Sb}}_6$.

We investigate the anomalous Hall effect (AHE) in GdFeCo/Pt, GdFeCo/SiN, and GdFeCo/Ta amorphous ferrimagnet/heavy-metal heterostructures for a wide temperature range including the magnetization compensation temperature. To take into account the peculiar temperature dependence of the magnetization in the ferrimagnet, the FeCo magnetization is extracted and used to normalize the anomalous Hall resistivity. From scaling law analysis, we find that AHE in GdFeCo/Pt and GdFeCo/Ta is mainly due to the intrinsic spin-Hall effect (SHE) occurring in the heavy-metal layers. Our results demonstrate the close correlation between the AHE and the SHE. Given that the AHE also originates in the heavy-metal layers, we also propose a circuit model that allows one to separate the AHE from the ferrimagnet layer and from the heavy-metal layer. In heterostructures of a poorly conductive magnetic layer and a heavy-metal layer, careful analysis is crucial to distinguish whether the AHE originates from the magnetic or the heavy-metal layer.

We show that moving dislocations generate giant effective local magnetic fields in a crystal lattice that can flip spins. Since massive creation of fast-moving dislocations is associated with a powerful elastic stress, this suggests a different mechanism of the magnetization reversal generated by laser or microwave beams or by electrically induced shear deformation.

The discovery of high-temperature superconductivity (SC) with $T_c\approx 80$ K in the pressurized ${\mathrm{La}}_3{\mathrm{Ni}}_2{\mathrm{O}}_7$ has aroused great interest. Currently, due to technical difficulties, most experiments on ${\mathrm{La}}_3{\mathrm{Ni}}_2{\mathrm{O}}_7$ can only be performed at ambient pressure. Particularly, various experiments have revealed the presence of a spin density wave (SDW) in the unidirectional diagonal double-stripe pattern with wave vector near $\pm (\pi /2,\pi /2)$ in ${\mathrm{La}}_3{\mathrm{Ni}}_2{\mathrm{O}}_7$ at ambient pressure. In this work, we employ first-principles calculations followed by the random phase approximation (RPA)-based study to clarify the origin of this special SDW pattern and the potential SC in ${\mathrm{La}}_3{\mathrm{Ni}}_2{\mathrm{O}}_7$ at ambient pressure. Starting from our density-functional-theory band structure, we construct an eight-band bilayer tight-binding model using the $\mathrm{Ni}\text{−}3d_{z^2}$ and $3d_{x^2-y^2}$ orbitals, which is equipped with the standard multiorbital Hubbard interaction. Our RPA calculation reveals an SDW order driven by Fermi surface nesting with wave vector $\mathit{Q}\approx (0,\pm 0.84\pi )$ in the folded Brillouin zone. From the view of the unfolded Brillouin zone, the wave vector turns to ${\mathit{Q}}_0\approx \pm (0.58\pi ,0.58\pi )$, which is near the one detected by various experiments. Further more, this SDW exhibits an interlayer antiferromagnetic order with a unidirectional diagonal double-stripe pattern, consistent with recent soft x-ray scattering experiments. This result suggests that the origin of the SDW order in ${\mathrm{La}}_3{\mathrm{Ni}}_2{\mathrm{O}}_7$ at ambient pressure can be well understood in the itinerant picture as driven by Fermi surface nesting. In the aspect of SC, our RPA study yields an approximate $s^{\pm }$-wave spin-singlet pairing with $T_c$ much lower than that under high pressure. Furthermore, the $T_c$ can be strongly enhanced through hole doping, leading to possible high-temperature SC at ambient pressure.

Ballistic heat transport and second sound propagation in solids is of direct relevance in electronic and energy applications at short length scales and low temperatures. Measurement or calculation of thermal conductivity, which is typically a primary objective, may be of limited usefulness for predicting heat transport which does not follow the heat-diffusion equation. In this paper, molecular-dynamics simulations of hexagonal BN are used to compute thermal response functions from equilibrium correlation functions defined in Fourier space. The response functions are useful for describing the time-dependent transport beyond the usual assumptions of Fourier's law. The results demonstrate that for length scales $\sim 110\mathrm{nm}$ at $T=100\mathrm{K}$ second sound should be experimentally observable. At higher temperatures and longer length scales, while second sound may not be directly observable, thermal transport can nevertheless strongly deviate from predictions based on the heat-diffusion equation. Along with classical simulations, we outline a first-principles, many-body theoretical approach for calculation of the response function based on solutions of the Bethe-Salpeter equation. The relevant expressions for heat current clarify the importance of phase coherence within a phonon branch to the observation of second sound. Previous work on one-dimensional chains is also discussed to show that materials characterized by linear dispersion and simple phonon band structure should more readily display second sound.

This work explores spin-wave dynamics in magnetic nanotubes, focusing on the influence of the Dzyaloshinskii-Moriya interaction and curvature. The study uses analytical methods to examine how these factors influence the emergence of nonreciprocity in nanotubes with longitudinal magnetization along the axis or with a vortexlike magnetization. The interplay between exchange, Dzyaloshinskii-Moriya, and dipolar couplings in determining the chirality of spin waves is discussed. When the magnetization is saturated along an axis, the spin waves propagating along it are symmetric under the inversion of the axial wave vector. However, magnetochirality, mainly driven by exchange and Dzyaloshinskii-Moriya couplings, is observed in the azimuthal modes. In the vortex state, frequency nonreciprocity occurs for waves propagating along the tube, while the azimuthal modes remain reciprocal. For positive Dzyaloshinskii-Moriya interaction, and depending on the helicity of the vortex, the asymmetry induced by the dipolar interaction is reinforced, whereas a negative coupling opposes this asymmetry. The influence of radial anisotropy is also examined. It is found that radial anisotropy reduces the frequency of the modes and shifts the dispersion minimum to a finite wave vector in the vortex state. The properties of modes near zero frequency offer insight into the emergence of chiral magnetic textures.

Temperature and field dependences of the frequencies of uniform modes of the skyrmion lattice in a two-dimensional ferromagnetic film with Dzyaloshinskii-Moriya interaction, as well as their damping, are computed within the model of classical spins. We show that the magnetization of the film exhibits Rabi-like oscillations when subjected to the microwave field at resonance with the low-frequency mode. Melting of the skyrmion lattice by resonant microwaves is investigated in terms of the time dependence of the orientational and translational order parameters. A distinct single-stage melting transition has been observed.

Rare-earth (RE) compounds have been of enormous interest in condensed matter physics as a platform for the exploration of interesting physical phenomena. Here, we report the successful single-crystal growth of $\mathrm{Ho}{\mathrm{B}}_2$, which exhibits a paramagnetic (PM)-ferromagnetic (FM) phase transition at 15 K and another phase transition at 11 K, and the discovery of a highly anisotropic magnetic phase diagram of this FM diboride. Magnetization measurements suggest that the ferromagnetically ordered moments of $\mathrm{H}{\mathrm{o}}^{3+}$ ions are oriented at a direction tilted by 50° from the $ab$ plane at 2 K, and they rotate largely toward the $ab$-plane direction upon application of a magnetic field but hardly toward the $c$-axis direction. Heat capacity and electrical resistivity measurements clearly demonstrate that the low-temperature phase transition at 11 K occurs even under high magnetic fields along the $ab$-plane direction, whereas it disappears immediately by magnetic fields along the $c$-axis direction. Moreover, the field-induced crossover phenomenon between FM and PM phases is found to be more promoted when applying a magnetic field along the $ab$-plane direction. The resulting magnetic phase diagram reveals that in-plane magnetic anisotropy is predominant in the present system, which contradicts the previous report of a spin-reorientation phenomenon toward the $c$-axis direction between 11 and 15 K. Taken together, the present findings suggest the presence of strong competition between in-plane and out-of-plane magnetic anisotropies in $\mathrm{Ho}{\mathrm{B}}_2$, giving rise to the unique FM spin arrangement.

Noise and current measurements are key tools for studying mesoscopic systems, revealing insights beyond conductance alone. For instance, noise measurements show that transport carriers in conventional superconductors have charge $2e$. The noise power also depends on junction type, distinguishing different transport processes. Existing theories focus primarily on zero-temperature shot noise in tunnel junctions with conventional superconductors, where transport is carried by quasiparticles and Cooper pairs. Here we develop a full counting statistics theory for unconventional superconductor/normal metal junctions of different types, incorporating the effect of thermal noise on the differential Fano factor, the ratio of differential noise power, and conductance. In these junctions there is a third type of transport mechanism, surface Andreev bound states. Our study reveals that junctions with dispersionless surface Andreev bound states exhibit negative differential Fano factor at finite temperatures. In contrast, in the presence of dispersive surface Andreev bound states, the noise power always increases with voltage, but there are local minima in the differential noise at those voltages corresponding to the extrema of the surface Andreev bound state spectrum. For normal metals and conventional superconductors the voltage dependence of the differential Fano factor is similar in all types of junctions, including tunnel junctions and diffusive barriers. However, significant differences arise with unconventional superconductors, making distinct junction types valuable tools for identifying pairing symmetries. Our results also highlight the importance of finite temperature effects in noise-power measurements for potential unconventional superconductors, offering new means to determine pairing symmetries in topological superconductors.