Results are reported for single crystals of the PbFCl-type layered compound ${\mathrm{ZrP}}_{1.27}{\mathrm{Se}}_{0.73}$ that were produced using the iodine vapor transport method. Electrical transport, magnetization, and heat capacity measurements reveal disordered metallic behavior and the occurrence of bulk superconductivity, with a transition temperature $\left(T_c\right)$ of 7.1 K and an anisotropic orbitally limited upper critical field. ${}^{31}\mathrm{P}$ nuclear magnetic resonance measurements provide additional microscopic information, where the line shape, Knight shift, and spin-lattice relaxation data are consistent with the superconductivity originating from the corrugated Zr-P(2c)/Se plane. This suggests that the superconductivity first forms in the corrugated plane and the bulk superconductivity eventually occurs via coupling between the square planar layers. These data also show that either there are multiple superconducting gaps or there is a single gap that does not fully open across the entire Fermi surface. These results clarify the superconducting state in this material and will enable further measurements that require single-crystal specimens.

Since spin can be regarded as a dummy degree of freedom, light-element topological semimetals (TSMs) are expected to be a promising alternative for spin-orbit-coupling based TSMs, which usually contain costly and toxic heavy elements. Using first-principles calculations combined with a bottom-up assembly strategy, herein we identify an intriguing light-element TSM, termed 3D borophene, which can be obtained by stacking synthesized 2D triangular borophene along the perpendicular direction. Under the protection of mirror symmetry, the linear band crossings between $\mathrm{B}-p_{xz}$ and $p_y$ states in the vicinity of the Fermi energy form two Weyl nodal lines running across the Brillouin zone in the $k_y=0$ plane. When the nodal lines are projected on the (010) surface, drumheadlike surface states and open Fermi arcs are observed, which provide vital evidence for experimental identification. Remarkably, by examining the defined slope index of the crossing bands in all possible $\mathit{k}$ paths, we find that the nodal lines of 3D borophene are composed of type-II Weyl points due to the emergence of tilted Weyl cones. Our findings not only establish a lightweight Weyl-nodal-line semimetal, but also highlight a bottom-up assembly strategy for designing desirable TSMs from synthetic 2D materials.

The exact solution of Kitaev's spin-$1/2$ honeycomb spin-liquid model has sparked an intense search for Mott insulators hosting bond-dependent Kitaev interactions, of which ${\mathrm{Na}}_2{\mathrm{IrO}}_3$ and $\alpha \text{−}\mathrm{Ru}{\mathrm{Cl}}_3$ are prime examples. Subsequently, it has been proposed that also spin-1 and spin-$3/2$ analogs of Kitaev interactions may occur in materials with strong spin-orbit coupling. As a minimal model to describe these Kitaev materials, we study the Heisenberg-Kitaev Hamiltonian in a consistent $1/S$ expansion, with $S$ being the spin size. We present a comprehensive study of this model in the presence of an external magnetic field applied along two different directions, [001] and [111], for which an intricate classical phase diagram has been reported. In both settings, we employ spin-wave theory in a number of ordered phases to compute phase boundaries at the next-to-leading order in $1/S$ and show that quantum corrections substantially modify the classical phase diagram. More broadly, our work presents a consistent route to investigate the leading quantum corrections in spin models that break spin-rotational symmetry.

Because of its two-dimensional structure and semiconducting properties, tin disulfide $\left({\mathrm{SnS}}_2\right)$ is of interest for many applications, such as photocatalysis, photovoltaics, sensing, and electronics. While the atomic and electronic structure of bulk and monolayer ${\mathrm{SnS}}_2$ have been studied, much less is known about the edges of layers. Such edges could have a major influence on the performance of ${\mathrm{SnS}}_2$. This paper reports on density functional theory (DFT) simulations of the atomic and electronic structure of the edges of ${\mathrm{SnS}}_2$. We modeled several different edge terminations at various S coverages and orientations, as well as performed thermodynamic analysis of edge terminations. Our results show that edges with 0% and 50% S atoms are most stable and that higher S coverage are unstable. We directly link edge stability with environmental temperature and pressure, which will guide the experimental synthesis of ${\mathrm{SnS}}_2$ materials. We found all the edges to be semiconducting, unlike other metal chalcogenides, and that the band gap energy decreased with increasing S coverage. Semiconducting edges could lead to lower charge recombination rates and better photocatalytic performance. Our calculations also show that edges may have direct or indirect band gaps, depending on the edge termination. Finally, we examined the reactivity of edges through hydrogen dissociation and found edges to be more reactive than basal planes. Our work provides important details on the nature of ${\mathrm{SnS}}_2$ edges and how these edges influence the electrical and chemical features of ${\mathrm{SnS}}_2$.

We unveil a previously overlooked wave propagation regime in magnetized plasmonic (gyrotropic) materials with comparable plasma and cyclotron frequencies, which enables a giant and broadband (nondispersive) nonreciprocal response. We show that this effect is due to a natural form of dispersion compensation that ultimately originates from the subtle implications of the principle of causality for gyrotropic plasmonic media, which allows the existence of a low-loss frequency window with anomalous nonmonotonic dispersion for the extraordinary mode. This is in stark contrast with conventional nongyrotropic passive materials, for which the frequency derivative of the permittivity dispersion function is always positive in low-loss regions. These findings may pave the way for superior nonreciprocal components in terms of bandwidth of operation and compactness, with orders-of-magnitude reductions in size. As a relevant example, we consider indium antimonide (InSb) to theoretically demonstrate a deeply subwavelength, broadband, THz isolator operating under moderate magnetic bias and at room temperature.

We show analytically that the ability of Dirac materials to localize an electron in both a barrier and a well can be utilized to open a pseudogap in graphene's spectrum. By using narrow top gates as guiding potentials, we demonstrate that graphene bipolar waveguides can create a nonmonotonous one-dimensional dispersion along the electron waveguide, whose electrostatically controllable pseudoband gap is associated with strong terahertz transitions in a narrow frequency range.

The surface atomic and electronic structure after deposition of one-third of a monolayer Te on Cu(111) was determined using a combination of low-energy electron diffraction (LEED), scanning tunneling microscopy and spectroscopy (STM/STS), angle-resolved single and two-photon photoelectron spectroscopy (ARPES /AR-2PPE), and density functional theory (DFT) calculations. Contrary to the current state in literature, Te does not create a two-dimensional surface alloy but forms ${\mathrm{Cu}}_2{\mathrm{Te}}_2$ adsorbate chains in a $\left(2\sqrt{3}\times \sqrt{3}\right){\text{R30}}^{\circ }$ superstructure. We establish this by a high-precision LEED-IV structural analysis with Pendry $R$ factor of $R=0.099$ and corroborating DFT and STM results. The electronic structure of the surface phase is dominated by an anisotropic downward dispersing state at the Fermi energy $E_F$ and a more isotropic upward dispersing unoccupied state at $E-E_F=+1.43\text{eV}$. Both states coexist with bulk states of the projected band structure, and are therefore surface resonances.

We investigate a heat engine with a finite-length Kitaev chain in an ideal Otto cycle. It is found that the critical point of the topological phase transition coincides with the maxima of the efficiency and work output of the total Otto engine. Finite-size effects are taken into account using the method of Hill's nanothermodynamics, as well as using the method of temperature-dependent energy levels. We identify the bulk and boundary thermal cycles of the Kitaev chain engine and find that they are nonideal Otto cycles. The physics of deviation from ideal Otto cycle is identified as a finite-size effect, which we dub as “internal geometric friction,” leading to heat transfer from the bulk to the boundary during the adiabatic transformation of the whole system. In addition, we determine the regimes allowing for independently running an ideal Otto refrigerator at the boundary and ideal Otto engines in the bulk and in the whole system. Furthermore, we show that the first-order phase transition in the boundary and the second-order phase transition in the bulk can be identified through their respective contributions to the engine work output.

The Rosenzweig-Porter model has seen a resurgence in interest as it exhibits a nonergodic extended phase between the ergodic extended metallic phase and the localized phase. Such a phase is relevant to many physical models from the Sachdev-Ye-Kitaev model in high-energy physics and quantum gravity to the interacting many-body localization in condensed-matter physics and quantum computing. This phase is characterized by fractal behavior of the wave functions and a postulated correlated miniband structure of the energy spectrum. Here we will seek evidence for the latter in the spectrum. Since this behavior is expected on intermediate energy scales, spectral rigidity or number variance is a natural way to tease it out. Nevertheless, due to the Thouless energy and ambiguities in the unfolding procedure, the results are inconclusive. On the other hand, by using the singular-value decomposition method, clear evidence for a super-Poissonian behavior in this regime emerges, consistent with a picture of correlated minibands.

The Mott transition is usually considered as resulting from the divergence of the effective mass of the quasiparticle in the Fermi-liquid theory; the dispersion relation around the Fermi level is considered to become flat toward the Mott transition. Here, to clarify the characterization of the Mott transition under the assumption of a Fermi-liquid-like ground state, the electron-addition excitation from the Gutzwiller wavefunction in the $t\text{−}J$ model is investigated on a chain, ladder, square lattice, and bilayer square lattice in the single-mode approximation using a Monte Carlo method. The numerical results demonstrate that an electronic mode that is continuously deformed from a noninteracting band at zero electron density loses its spectral weight and gradually disappears toward the Mott transition. It exhibits essentially the magnetic dispersion relation shifted by the Fermi momentum in the small-doping limit as indicated by recent studies for the Hubbard and $t\text{−}J$ models, even if the ground state is assumed to be a Fermi-liquid-like state exhibiting gradual disappearance of the quasiparticle weight. This implies that, rather than as the divergence of the effective mass or disappearance of the carrier density that is expected in conventional single-particle pictures, the Mott transition can be better understood as freezing of the charge degrees of freedom while the spin degrees of freedom remain active, even if the ground state is like a Fermi liquid.

The one-dimensional (1D) metallic states that appear at the zigzag edges of semiconducting two-dimensional transition metal dichalcogenides (TMDCs) result from the intrinsic electric polarization in these materials, which for ${\mathrm{D}}_{3h}$ symmetry is a topological invariant. These 1D states are susceptible to electronic and structural perturbations that triple the period along the edge. In this paper we study possible spin-density waves (SDWs) and charge-density waves (CDWs) at the zigzag edges of ${\mathrm{MoS}}_2$, using first-principles density-functional theory calculations. Depending on the detailed structures and termination of the edges, we observe either combined SDW/CDWs or pure CDWs, along with structural distortions. In all cases the driving force is the opening of a band gap at the edge. The analysis should hold for all group VI TMDCs with the same basic structure as ${\mathrm{MoS}}_2$.

The most promising mechanisms for the formation of Majorana bound states (MBSs) in condensed matter systems involve one-dimensional systems [such as semiconductor nanowires, magnetic chains, and quantum spin Hall insulator (QSHI) edges] proximitized to superconducting materials. The choice between each of these options involves tradeoffs between several factors such as reproducibility of results, system tunability, and robustness of the resulting MBS. In this paper, we propose that a combination of two of these systems, namely, a magnetic chain deposited on a QSHI edge in contact with a superconducting surface, offers a better choice of tunability and MBS robustness compared to magnetic chain deposited on bulk. We study how the QSHI edge interacts with the magnetic chain, and see how the topological phase is affected by edge proximity. We show that MBSs near the edge can be realized with lower chemical potential and Zeeman field than the ones inside the bulk, independently of the chain's magnetic order (ferromagnetic or spiral order). Different magnetic orderings in the chain modify the overall phase diagram, even suppressing the boundless topological phase found in the bulk for chains located at the QSHI edge. Moreover, we quantify the “quality” of MBSs by calculating the Majorana polarization (MP) for different configurations. For chains located at the edge, the MP is close to its maximum value already for short chains. For chains located away from the edge, longer chains are needed to attain the same quality as chains located at the edge. The MP also oscillates in phase with the in-gap states, which is relatively unexpected as peaks in the energy spectrum correspond to stronger overlap of MBSs.

We predict electric-field-driven exciton vortices in transition metal dichalcogenide monolayers in the Bose-Einstein condensation regime. The Rashba spin-orbit coupling created by perpendicular electric fields couples the bright and dark excitons, behaves like an emerging SU(2) gauge field for excitons, and induces spatially asymmetric distribution of exciton density. We find the interplay between the dipole-dipole interaction among excitons and Rashba spin-orbit coupling leads to the phase transitions containing different vortices, from a single pair of vortices to numerous satellite vortices appearing at the edge of the sample. The exciton condensation at the $K$ and $K^{\prime }$ valleys shows mirror-symmetric patterns composed of exciton vortices rotating oppositely, which are protected topologically by the winding numbers.

We theoretically investigate photoinduced phenomena induced by time-periodic driving fields in two-dimensional electron gases under perpendicular magnetic fields with Rashba spin-orbit coupling. Using perturbation theory, we provide analytical results for the Floquet-Landau energy spectrum appearing due to THz radiation. By employing the resulting photomodulated states, we compute the dynamical evolution of the spin polarization function for an initially prepared coherent state. We find that the interplay of the magnetic field, Rashba spin-orbit interaction, and THz radiation can lead to nontrivial beating patterns in the spin polarization. The dynamics also induces fractional revivals in the autocorrelation function due to interference of the photomodulated quantum states. We calculate the transverse photoassisted conductivity in the linear response regime using Kubo formalism and analyze the impact of the radiation field and Rashba spin-orbit interaction. In the static limit we find that our results reduce to well-known expressions of the conductivity in nonrelativistic and quasirelativistic (topological insulator surfaces) two-dimensional electron gas thoroughly described in the literature. We discuss the possible experimental detection of our theoretical prediction and their relevance for spin-orbit physics at high magnetic fields.

We study the quench dynamics of the three-dimensional Kitaev (spin) model under a linear drive using both exact numerical calculations and analytical independent crossing approximation. Unlike the two-dimensional Kitaev model, the three-dimensional Kitaev model reduces to a multilevel Landau-Zener problem for each momentum. We show that for the slow quench, the defect density is proportional to the quench rate $1/\tau$. We find that the zeros of the relevant coupling between the levels determine the nonadiabatic condition for the production of defects. The contour on which the energy spectrum becomes gapless does not play an active role. The asymptotic behavior of the defect density crucially depends on the way the system reaches the nonadiabatic regime during the quenching process. We analytically show that defect correlation varies as ${\tau }^{-1}{e}^{-A/\tau }$ where $A$ is a constant independent of $\tau$. For the slow quench, the qualitative dependence of the entropy (produced during the quenching process) on the quench time is the same as that of the defect correlation, indicating a close connection between the defect correlation and the entropy content of the final state. Possible experimental realization of such quench dynamics is also described briefly.

The study of dissipation and decoherence in generic open quantum systems recently led to the investigation of spectral and steady-state properties of random Lindbladian dynamics. A natural question is then how realistic and universal those properties are. Here, we address these issues by considering a different description of dissipative quantum systems, namely, the discrete-time Kraus map representation of completely positive quantum dynamics. Through random matrix theory (RMT) techniques and numerical exact diagonalization, we study random Kraus maps, allowing for a varying dissipation strength, and their local circuit counterpart. We find the spectrum of the random Kraus map to be either an annulus or a disk inside the unit circle in the complex plane, with a transition between the two cases taking place at a critical value of dissipation strength. The eigenvalue distribution and the spectral transition are well described by a simplified RMT model that we can solve exactly in the thermodynamic limit, by means of non-Hermitian RMT and quaternionic free probability. The steady state, on the contrary, is not affected by the spectral transition. It has, however, a perturbative crossover regime at small dissipation, inside which the steady state is characterized by uncorrelated eigenvalues. At large dissipation (or for any dissipation for a large-enough system), the steady state is well described by a random Wishart matrix. The steady-state properties thus coincide with those already observed for random Lindbladian dynamics, indicating their universality. Quite remarkably, the statistical properties of the local Kraus circuit are qualitatively the same as those of the nonlocal Kraus map, indicating that the latter, which is more tractable, already captures the realistic and universal physical properties of generic open quantum systems.

The ability to convert spin accumulation to charge currents is essential for applications in spintronics. In semiconductors, spin-to-charge conversion is typically achieved using the inverse spin Hall effect or using a large magnetic field. Here we demonstrate a general method that exploits the nonlinear interactions between spin and charge currents to perform all-electrical, rapid, and noninvasive detection of spin accumulation without the need for a magnetic field. We demonstrate the operation of this technique with ballistic GaAs holes as a model system with strong spin-orbit coupling, in which a quantum point contact provides the nonlinear energy filter. This approach is generally applicable to electron and hole systems with strong spin-orbit coupling.

The internal magnetic field in a sodium battery compound, i.e., the paramagnet ${\mathrm{Na}}_{0.7}{\mathrm{CoO}}_2$, was investigated with negative muon spin rotation and relaxation (${\mu }^{-}\mathrm{SR}$), and the result was compared with the results previously obtained with ${\mu }^{+}\mathrm{SR}$. The majority of implanted ${\mu }^{-}$ is captured on an oxygen nucleus, while ${\mu }^{+}$ locates an interstitial site. Therefore, a ${\mu }^{\pm }\mathrm{SR}$ work provides information on the internal magnetic field, which is formed by nuclear magnetic moments of ${}^{23}\mathrm{Na}$ and ${}^{59}\mathrm{Co}$, from the two different viewpoints. Besides a slight decrease in the field distribution width ($\mathrm{\Delta }$) around 300 K, the nuclear magnetic field detected with ${\mu }^{-}\mathrm{SR}$ was found to be almost static and temperature independent up to 400 K, even though Na ions are known to start to diffuse above 290 K based on ${\mu }^{+}\mathrm{SR}$, Na-NMR, neutron scattering, and electrochemical measurements. Such a discrepancy is caused by the fact that the Na contribution to $\mathrm{\Delta }$ is only about 3% at the O site whereas it is about 13% at the interstitial site, where the ${\mu }^{+}$ is presumably located.

In the present paper, the magnetic structure and spin reorientation of mixed rare-earth orthoferrite ${\mathrm{Nd}}_{0.5}{\mathrm{Dy}}_{0.5}\mathrm{Fe}{\mathrm{O}}_3$ have been investigated. At room temperature, our neutron-diffraction measurements reveal that the magnetic structure of ${\mathrm{Fe}}^{3+}$ spins in ${\mathrm{Nd}}_{0.5}{\mathrm{Dy}}_{0.5}\mathrm{Fe}{\mathrm{O}}_3$ belongs to ${\mathrm{\Gamma }}_4$ irreducible representation ($G_x, F_z$) as observed in both parent compounds ($\mathrm{Nd}\mathrm{Fe}{\mathrm{O}}_3$ and $\mathrm{Dy}\mathrm{Fe}{\mathrm{O}}_3$). The neutron-diffraction study also confirms the presence of a spin-reorientation transition where the magnetic structure of ${\mathrm{Fe}}^{3+}$ spins changes from ${\mathrm{\Gamma }}_4$ to ${\mathrm{\Gamma }}_2(F_x, G_z$) representation between 75 and 20 K while maintaining a G-type antiferromagnetic configuration. Such a gradual spin reorientation is unusual since the large single ion anisotropy of ${\mathrm{Dy}}^{3+}$ ions is expected to cause an abrupt ${\mathrm{\Gamma }}_4\to {\mathrm{\Gamma }}_1(G_y$) rotation of the ${\mathrm{Fe}}^{3+}$ spins. At 10 K, the ${\mathrm{Fe}}^{3+}$ magnetic structure is represented by ${\mathrm{\Gamma }}_2$ ($F_x, G_z$). Unexpectedly, the ${\mathrm{\Gamma }}_4$ structure of ${\mathrm{Fe}}^{3+}$ spins re-emerges below 10 K, which also coincides with the development of rare-earth (${\mathrm{Nd}}^{3+}/{\mathrm{Dy}}^{3+}$) magnetic ordering having $c_y^R$ configuration. Such re-emergence of a magnetic structure has been a rare phenomenon in orthoferrites. The absence of a second-order phase transition in rare-earth ordering, interpreted from heat capacity data, suggests the prominent role of ${\mathrm{Nd}}^{3+}-{\mathrm{Fe}}^{3+}$ and ${\mathrm{Nd}}^{3+}-{\mathrm{Dy}}^{3+}$ exchange interactions. These interactions suppress the independent rare-earth magnetic ordering observed in both parent compounds due to ${\mathrm{Nd}}^{3+}/{\mathrm{Dy}}^{3+}-{\mathrm{Nd}}^{3+}/{\mathrm{Dy}}^{3+}$ exchange interactions. Our density-functional-theory calculations including Coulomb correlation and spin-orbit interaction effects ($\mathrm{DFT}+U+\mathrm{SO}$) reveal that the C-type arrangement of rare-earth ions (${\mathrm{Nd}}^{3+}/{\mathrm{Dy}}^{3+}$), with ${\mathrm{\Gamma }}_2$ ($F_x, G_z$) configuration for ${\mathrm{Fe}}^{3+}$ moments, is energetically very close to a phase with the same rare-earth magnetic ordering but ${\mathrm{\Gamma }}_4$ ($G_x, F_z$) configuration of ${\mathrm{Fe}}^{3+}$ spins. Further, the ${\mathrm{Nd}}^{3+}-{\mathrm{Fe}}^{3+}$ and ${\mathrm{Nd}}^{3+}-{\mathrm{Dy}}^{3+}$ exchange interactions are observed to play significant roles in the complex ${\mathrm{Fe}}^{3+}$ spin reorientation with the re-emergence of ${\mathrm{\Gamma }}_4$ at low temperature. Consistent with the experimental observations, our calculations established the mixed phase (${\mathrm{\Gamma }}_2$ and ${\mathrm{\Gamma }}_4$) to be the magnetic ground state of ${\mathrm{Fe}}^{3+}$ moments.