The behavior in magnetic field of a paramagnetic center is characterized by its $g$ tensor. An anisotropic form of the latter implies different kind of response along different crystallographic directions. Here we shed light on the anisotropy of the $g$ tensor of ${\mathrm{Yb}}^{3+}4f^{13}$ ions in ${\mathrm{NaYbS}}_2$ and ${\mathrm{NaYbO}}_2$, layered triangular-lattice materials suggested to host spin-liquid ground states. Using quantum chemical calculations we show that, even if the ligand-cage trigonal distortions are significant in these compounds, the decisive role in realizing strongly anisotropic, noncubic $g$ factors is played by interlayer cation charge imbalance effects. The latter refer to the asymmetry experienced by a given Yb center due to having higher ionic charges at adjacent metal sites within the magnetic $ab$ layer, i.e., $3+$ nearest neighbors within the $ab$ plane versus $1+$ species between the magnetic layers. According to our results, this should be a rather general feature of $4f^{13}$ layered delafossites: less interlayer positive charge is associated with stronger in-plane magnetic response.

Manipulating collectively ordered electronic and magnetic states in a correlated system is at the core of condensed matter physics. Besides tuning the carrier density of a crystal, the latest developed field-effect transistor (FET) with a solid ion conductor (SIC) can also drive ions into the crystal and lead to structural transformations that are difficult to access with conventional methods including conventional field-effect transistors. Here, we exploit the SIC-FET gating technique to realize a metastable phase in (Li,Fe)OHFeS thin flakes, and achieve a rich phase diagram involving superconductivity, soft ferromagnetism, and hard ferromagnetism. With the injection of Li ions into the thin flake, the superconductivity is gradually suppressed and a soft ferromagnetic phase with new crystal structure sets in, evidenced by the anomalous Hall effect and magnetoresistance measurements. Further injecting Li ion drives the soft ferromagnetic state into a hard ferromagnetic state, where different types of magnetic interactions dominate due to the simultaneous tuning of carrier density and magnetic Fe ion concentration in the Li ion injection process. Our paper paves a way to control structural phase transformations as well as physical properties by the electric field. These findings demonstrate the superior performance of the SIC-FET in regulating the physical properties of layered crystals and its potential applications for multifunctional devices.

Strains in superconductors due to moving vortices and vortex lattices are discussed. It is shown that the energy stored in elastic strains increases with vortex velocity. For moving vortex lattices, the elastic energy depends on velocity orientation relative to the lattice having minimum for the velocity directed along one of the unit cell vectors of the moving lattice. It is shown that for supersonic motion, the vortex-induced stress field has a shape similar to supersonic shock waves.

The high-frequency dielectric behavior of uniaxial tungsten-bronze strontium barium niobate crystals with various Sr/Ba ratios, including both ferroelectric and relaxor compositions, have been studied in a broad frequency range (${10}^4$ to ${10}^{13}\mathrm{Hz}$) and temperature interval 100–500 K in order to thoroughly understand the evolution of the relaxation dynamics across the ferroelectric phase transition. The dielectric response along the polar axis consists of three relaxations corresponding to polarization mechanisms related to several correlation lengths of mesoscopic order. All of them show dissimilar behaviors with temperature, pointing out to their distinct nature. A temperature-dependent central mode at THz frequencies and a relaxation above 10 GHz are accompanied by the slowing down of a relaxation in the MHz range. This response reveals the complex mechanism of the phase transition and supports the coexistence of displacive and order-disorder scenarios. Relaxor and ferroelectric compositions surprisingly reveal similar qualitative behavior within the frequency window used. However, relaxor crystals display relaxations at higher frequency because of the smaller extent of the polar fluctuations and ferroelectric regions, which coexist in almost all the compositions. The presence of two different ferroelectric subsystems in the structure agrees with the existence of several polarization mechanisms involved in the complex dielectric and ferroelectric response.

We unveil the role of the long-time average of the Loschmidt echo in the characterization of nonequilibrium quantum phase transitions by studying sudden quench processes across quantum phase transitions in various quantum systems. While the dynamical quantum phase transitions are characterized by the emergence of a series of zero points at critical times during time evolution, we demonstrate that nonequilibrium quantum phase transitions can be identified by nonanalyticities in the long-time average of the Loschmidt echo. The nonanalytic behaviors are illustrated by a sharp change in the long-time average of the Loschmidt echo or the corresponding rate function or the emergence of divergence in the second derivative of the rate function when the driving quench parameter crosses the phase transition points. The connection between the second derivative of the rate function and fidelity susceptibility is also discussed.

Non-Hermitian topological phases in static and periodically driven systems have attracted great attention in recent years. Finding dynamical probes for these exotic phases would be of great importance for the detection and application of their topological properties. In this work, we introduce an approach to dynamically characterize non-Hermitian Floquet topological phases in one dimension with chiral symmetry. We show that the topological invariants of a chiral-symmetric Floquet system can be fully determined by measuring the winding angles of its time-averaged spin textures. We further purpose a piecewise quenched lattice model with rich non-Hermitian Floquet topological phases, in which our theoretical predictions are numerically demonstrated and compared with another approach utilizing the mean chiral displacement of a wave packet.

We report a thorough study of ${\mathrm{Y}}_{0.7}{\mathrm{La}}_{0.3}{\mathrm{VO}}_3$ single crystals by measuring magnetic properties, specific heat, thermal conductivity, Raman scattering, x-ray and neutron diffraction with the motivation of revealing the lattice response to the spin-orbital entanglement in $R{\mathrm{VO}}_3$. Upon cooling from room temperature, the orbitally disordered paramagnetic state changes around $T^{*}\sim 220$ K to a spin-orbital entangled state which is then followed by a transition at $T_N = 116$ K to $C$-type orbital-ordered (OO) and $G$-type antiferromagnetic ordered (AF) ground state. In the temperature interval $T_N<T<T^{*}$, the ${\mathrm{VO}}_{6/2}$ octahedra have two comparable in-plane V-O bonds which are longer than the out-of-plane V-O1 bond. This octahedral site distortion supports the spin-orbital entanglement of partially filled and degenerate yz/zx orbitals. However, this distortion is incompatible with the steric octahedral site distortion intrinsic to orthorhombic perovskites. Their competition induces a second-order transition from the spin-orbital entangled state to a $C$-OO/$G$-AF ground state where the long-range OO suppresses the spin-orbital entanglement. Our analysis suggests that the spin-orbital entangled state and $G$-OO are comparable in energy and compete with each other. Rare-earth site disorder favors the spin-orbital entanglement rather than a cooperative Jahn-Teller distortion. The results also indicate for ${\mathrm{LaVO}}_3$ a $C$-OO/$G$-AF state in $T_t \le T \le T_N$ and an orbital flipping transition at $T_t$.

The effect of isovalent substitution of rare-earth cations on the phase separation in half-doped manganites was studied on the example of ${\mathrm{Sm}}_{0.32}{\mathrm{Pr}}_{0.18}{\mathrm{Sr}}_{0.5}{\mathrm{MnO}}_3$ by high-resolution neutron powder diffraction, neutron beam depolarization, second-harmonic magnetic response, and magnetization and resistivity measurements from 4 K up to room temperature and higher. A structural phase transition from the orthorhombic $Pbnm$ phase to a mixture of $Pbnm$ and monoclinic $P{2}_1/m$ phases was observed upon cooling. The magnetic ground state was found to be phase-separated into three magnetic phases emerging at different temperatures, viz., ferromagnetic (FM) and antiferromagnetic A and charge-ordered CE types. FM clusters arise far above room temperature in the orthorhombic phase and coalesce upon cooling to produce the long-range FM order below 250 K and to arrive at the percolative FM phase below 120 K. The A- and CE-type orders form in the monoclinic phase at the temperatures 200 K and 120 K, respectively. The Sm/Pr isovalent substitution qualitatively changes the phase separation and significantly increases its temperature range compared to the parent compounds. The results obtained give us knowledge of phase separation occurring in systems with strong electron correlations and extend opportunities for fine-tuning of their properties.

We report on the measurements of the magnetization and heat capacity of the tetragonal heavy-fermion compound ${\mathrm{Ce}}_2{\mathrm{RhIn}}_8$, dependent on the direction of the magnetic field applied perpendicular to the $c$ axis. A notable anisotropic magnetization component having a fourfold symmetry has been observed in the antiferromagnetic state in low fields. The angular dependence of the heat capacity does not indicate any additional phase which implies that the observed magnetization anisotropy is an intrinsic property of ${\mathrm{Ce}}_2{\mathrm{RhIn}}_8$. A clear angular dependence of magnetic phase boundaries on the applied magnetic field has been also revealed. A possible interpretation of these results is discussed in the context of previously reported studies of magnetic structures in ${\mathrm{Ce}}_2{\mathrm{RhIn}}_8$.

The generation and manipulation of magnetic skyrmions are perquisites for any skyrmion-based information processing devices, where skyrmions are used as nonvolatile information carriers. In this work, we report experimentally the skyrmion generation through the usage of a nonmagnetic conducting Ti/Au point contact in a device made of a $\mathrm{Ta}/\mathrm{CoFeB}/\mathrm{Ta}{\mathrm{O}}_x$ trilayer film. Moreover, the accompanied topological charge-dependent skyrmion dynamics, namely the skyrmion Hall effect, is also observed in the same device. The creation process of a skyrmion has been numerically reproduced through micromagnetic simulations, in which the important role of the skyrmion-antiskyrmion pair formation is identified. The motion and Hall effect of a skyrmion, immediately after its creation, is described using a modified Thiele equation after taking into account the contribution from spatially inhomogeneous spin-orbit torques and the Magnus force. Our results on the simultaneous generation and manipulation of skyrmions using a nonmagnetic point contact are useful for understanding the ultrafast dynamics of skyrmion creation, which could also provide an effective pathway for designing skyrmion-based devices.

The multiferroic behavior of ${\mathrm{CoCr}}_2{\mathrm{O}}_4$ results from the appearance of conical spin-spiral magnetic ordering, which induces electric polarization. The magnetic ground state has a complex size-dependent behavior, which collapses when reaching a critical particle size. Here the magnetic phase stability of ${\mathrm{CoCr}}_2{\mathrm{O}}_4$ in the size range of 3.6–14.0 nm is presented in detail using the combination of neutron diffraction with XYZ polarization analysis and macroscopic magnetization measurements. We establish critical coherent domain sizes for the formation of the spin spiral and ferrimagnetic structure and reveal the evolution of the incommensurate spin spiral vector with particle size. We further confirm the presence of ferroelectric polarization in the spin spiral phase for nanocrystalline ${\mathrm{CoCr}}_2{\mathrm{O}}_4$.

We report a comprehensive study of physical properties of the binary superconductor compound SnAs. The electronic band structure of SnAs was investigated using both angle-resolved photoemission spectroscopy (ARPES) in a wide binding energy range and density functional theory (DFT) within generalized gradient approximation (GGA). The DFT/GGA calculations were done including spin-orbit coupling for both bulk and (111) slab crystal structures. Comparison of the DFT/GGA band dispersions with ARPES data shows that the spectrum for the (111) slab much better describes ARPES data than that for the bulk. In addition, we studied experimentally superconducting properties of SnAs by specific heat, magnetic susceptibility, magnetotransport measurements, and Andreev reflection spectroscopy. Temperature dependencies of the superconducting gap and of the specific heat were found to be well consistent with those expected for the single band BCS superconductors with an isotropic $s$-wave order parameter. Despite spin-orbit coupling present in SnAs, our data show no signatures of a potential unconventional superconductivity, and the characteristic BCS ratio $2\mathrm{\Delta }/T_c=3.48–3.73$ is very close to the BCS value in the weak coupling limit.

In this paper we analyze the magnetization properties of an antiferromagnetic kagome-stripe lattice, motivated by the recent synthesis of materials exhibiting this structure. By employing a variety of techniques that include numerical methods such as density-matrix renormalization-group and Monte Carlo simulations, as well as analytical techniques such as perturbative low-energy effective models and exact solutions, we characterize the magnetization process and magnetic phase diagram of a kagome-stripe lattice. The model captures a variety of behaviors present in the two-dimensional kagome lattice, which are described here by analytical models and numerically corroborated. In addition to the characterization of semiclassical intermediate plateaus, it is worth noting the determination of an exact magnon crystal phase which breaks the underlying symmetry of the lattice. This magnon crystal phase generalizes previous findings.

We construct a supersymmetric model of interacting Majorana fermions on the kagome lattice. In the infinite-coupling limit, the model exhibits an extensively degenerate ground state manifold separated in two topological sectors, in addition to two parity supersectors. An exact solution for thin-torus geometries allows us to analytically construct the entire zero-energy ground state manifold. Upon inclusion of hopping terms with energy scale $g$, the supersymmetry is spontaneously broken with the ground state energy density scaling as $g^4$. We also briefly discuss the noninteracting limit of the model, which exhibits a zero-energy flat band and Majorana Chern bands.

Three-dimensional (3D) Dirac and Weyl semimetals are quantum states that have emerged in physics recently. But their intrinsic transport properties are quite elusive because of either the coexistence of Schrödinger fermions or the deviation of linear dispersion at Fermi level in previously proposed Dirac and Weyl semimetals. Here, we provide the theoretical and experimental evidences of an intrinsic Dirac state in the quaternary chalcogenide $\mathrm{C}{\mathrm{u}}_2\mathrm{HgSnS}{\mathrm{e}}_4$ that has bared linear dispersions in conduction bands. Scanning tunneling spectroscopy reveals the quadratic energy-dependent density of states within an extremely large energy range $(\sim 400\mathrm{meV})$ on conduction bands of $\mathrm{C}{\mathrm{u}}_2\mathrm{HgSnS}{\mathrm{e}}_4$, which is self-consistent with linear dispersion detected by angle-resolved photoemission spectroscopy. In electron-doped $\mathrm{C}{\mathrm{u}}_2\mathrm{HgSnS}{\mathrm{e}}_4$, positive magnetoresistance at low magnetic field $B(<2.5\mathrm{T})$ and negative magnetoresistance under high $B$ are observed, which is attributed to the chiral anomaly effect. However, conventional negative magnetoresistance is observed in hole-doped $\mathrm{C}{\mathrm{u}}_2\mathrm{HgSnS}{\mathrm{e}}_4$, which is attributed to weak localization broken by $B$. Remarkably, the carrier mobility has a ${10}^5$-fold decrease when the Fermi level is adjusted from conduction to valence bands. Our results suggest that $\mathrm{C}{\mathrm{u}}_2\mathrm{HgSnS}{\mathrm{e}}_4$ not only provides a playground for exploring intrinsic properties of 3D Dirac fermions but also is promising for developing high-speed, low-dissipation electronic devices.

We discuss a general diagnosis scheme for topological nodal lines protected by time-reversal symmetry and space-inversion symmetry in the absence of spin-orbit coupling. It is shown that when a shallow band inversion (with a small inverted gap) appears at the $\mathrm{\Gamma }$ point in the Brillouin zone, nodal lines are generated along with the inversion. Much information on the types and numbers of these nodal lines can be related to the rotation eigenvalues and inversion eigenvalues of the inverted bands. In addition, we establish a $\mathbb{Z}$-type monopole charge for nodal lines with fourfold or sixfold rotation axis. We point out that the new monopole charge is only well defined in a fragile sense, that is, when the orbitals near the Fermi energy are restricted to those having the same sign under a twofold rotation. The diagnosis scheme goes beyond the one discussed by Song et al. [Phys. Rev. X 8, 031069 (2018)], particularly when there is a band crossing along some high-symmetry line or when the nodal line has nonunity monopole charge.

We have investigated the spin polarization and orbital configuration of the spin-split surface states in a non-symmorphic semimetal HfSiS by spin- and angle-resolved photoelectron spectroscopy using polarized tunable photons combined with detailed theoretical calculations. We have found that the surface states surrounding the $\overline{X}$ point with $C_{2v}$ symmetry exhibit an exotic unidirectional spin texture coupled with $d_{yz}$ orbital. The observed unidirectional spin texture is well reproduced by the theoretical calculations. Our work clarifies the significance of orbital symmetry in the manipulation of spin orientations, providing an approach to realize the persistent spin texture for the prolonged spin-coherence time in spintronic applications.

Using first-principles calculations, we determine the role of compressive and tensile uniaxial and equibiaxial strain on the structural, electronic, and magnetic properties of ${\mathrm{V}}_2{\mathrm{O}}_3$. We find that compressive strain increases the energy to transition from the high-temperature paramagnetic metallic phase to the low-temperature antiferromagnetic insulating phase. This shift in the energy difference can be explained by changes in the V-V bond lengths that are antiferromagnetically aligned in the low-temperature structure. The insights that we have obtained provide a microscopic explanation for the shifts in the metal-insulator transition temperature that have been observed in experiments of ${\mathrm{V}}_2{\mathrm{O}}_3$ films grown on different substrates.