The tensors of conductivity and spin susceptibility of a two-dimensional electron gas (2DEG) with equal Rashba and Dresselhaus spin-orbit interaction constants [the persistent spin helix (PSH) state] in a parallel magnetic field are calculated. Applying a parallel magnetic field to the PSH state leads to the appearance of a saddle point in the spectrum and, accordingly, to a Van Hove singularity (VHS), whose amplitude increases indefinitely as the magnetic field strength $\left(\mathbf{b}\right)$ approaches to some critical value $b_{cr}$. The presence of a VHS in the density of states is an important factor determining the conductivity and spin susceptibility tensors. When only the lower spin subband is filled, the off-diagonal elements of the conductivity tensor are nonzero; that is, a Hall voltage arises due to the anisotropy of the Fermi surface and scattering. In the region where two spin subbands are filled, the diagonal and off-diagonal components of the spin susceptibility tensor are equal, and the off-diagonal terms of the conductivity tensor vanish. A sharp decrease in the conductivity and spin susceptibility at the beginning of the filling of the second spin subband, the ratio of the diagonal component of the spin susceptibility to the off-diagonal one, and also the number of critical points in the spectrum make it possible to establish the PSH 2DEG state.

Experiments observe an enhanced superconducting gap over impurities as compared to the clean-bulk value. In order to shed more light on this phenomenon, we perform simulations within the framework of Bogoliubov–de Gennes theory applied to the attractive Hubbard model. The simulations qualitatively reproduce the experimentally observed enhancement effect; it can be traced back to an increased local density of states at the Fermi energy in the metal close to the impurity site. In addition, the simulations display significant differences between a thin [two-dimensional (2D)] and a very thick [three-dimensional (3D)] film. In 2D pronounced Friedel oscillations can be observed, which decay much faster in 3D and therefore are more difficult to resolve. Also, this feature is in qualitative agreement with the experiment.

In optics, combining one-dimensional (1D) topological systems with lasers and nonlinear optics has promoted their rapid development. A 1D acoustic topological system can only achieve single-frequency acoustic waves localization, limiting its practicality. The implementation of tunable and integrated 1D topological systems will improve this situation. Here, we propose an electrically tunable and integrable 1D topological nanoelectromechanical phononic crystal. Different strong and weak couplings are formed by changing the overlapping degree of adjacent suspended circular membranes, accompanied by different topological properties for the phononic bandgaps. Topologically protected interface states exist at their interface, and these states are stable even after introducing various degrees of distortion. Narrow band-pass filters based on these interface states can be implemented, with adjusted operating frequency by different grid voltage. Our proposed electrically tunable and integrable structure holds potential for smart filtering and may facilitate the development of integrated electromechanical circuits.

Optical control and switching of domain configuration are intriguing to overcome the sluggish time response, hysteresis, and Joule heating losses present in conventional methods where resistive contacts are involved. The effective optical control of the domain configuration has remained challenging and far from fully understood. It has been reported that light polarization can be used to control the domain configuration in ${\mathrm{BaTiO}}_3$, however, without much focus on origin of its mechanism. By combining the experimental techniques that are sensitive to the local and average crystal structure and to electric polarization and electronic structure, we detect and demonstrate the optically guided variations in the domain configurations of ${\mathrm{BaTiO}}_3$ and show that the strain field generated through the bulk photovoltaic effect plays a key role in domain reconfiguration. Complete mechanism of reversible domain control via light polarization is discussed.

It is demonstrated by means of the optimal control theory that the energy cost of the spin-orbit torque induced reversal of a nanomagnet with perpendicular anisotropy can be strongly reduced by proper shaping of both in-plane components of the current pulse. The time dependence of the optimal switching pulse that minimizes the energy cost associated with joule heating is derived analytically in terms of the required reversal time and material properties. The optimal reversal time providing a tradeoff between the switching speed and energy efficiency is obtained. A sweet-spot balance between the fieldlike and dampinglike components of the spin-orbit torque is discovered; it permits for a particularly efficient switching by a down-chirped rotating current pulse whose duration does not need to be adjusted precisely.

We report magnetic and specific heat measurements at low temperatures ($>100$ mK) and high magnetic fields (up to 9 T) for the metalorganic compounds ${\mathrm{MnCl}}_2\text{−}4\mathrm{SC}{\left({\mathrm{NH}}_2\right)}_2$ (DTM) and ${\mathrm{FeCl}}_2\text{−}4\mathrm{SC}{\left({\mathrm{NH}}_2\right)}_2$ (DTF). Fits to the experimental data from the Curie-Weiss law and mean-field theory indicate the antiferromagnetic nature of both compounds. For temperatures down to $T=0.56$ K the compound DTM exhibits two successive transitions, which may be associated with different magnetic orderings. In this system the external magnetic field is a tuning parameter that allows us to access such magnetic phases separated by distinct quantum critical points. No indication of magnetic ordering is found in DTF down to 100 mK, making this compound a candidate for a strongly frustrated material with frustration parameter $f=|{\theta }_{\mathrm{CW}}|/T_N>100$. Finally, we discuss the absence of Bose-Einstein condensation of magnons and the possibility of a spin-orbital liquid state in DTF.

Recently, there are heavy debates concerning the topological nature of ${\mathrm{YbMnBi}}_2$ being a type-II Weyl semimetal with Mn moments having a canting angle of ${10}^{\mathrm{o}}$ or a Dirac semimetal without canting. In this paper, we systematically study the magnetic and topological properties of ${\mathrm{YbMnBi}}_2$ using density functional theory calculations. Our results unveil that bulk ${\mathrm{YbMnBi}}_2$ is a Dirac semimetal with a collinear antiferromagnetic spin order. By canting the magnetic moments of Mn ions, we surprisingly find that ${\mathrm{YbMnBi}}_2$ enters into the type-II Weyl state with a canting angle of $2^{\mathrm{o}}$. As Bi vacancies in Mn-Bi-Mn bonds can produce sizable Dzyaloshinskii-Moriya interactions and thus cant the magnetic moments of Mn ions, we argue that the possible Bi vacancies induce a topological phase transition from a Dirac semimetal to a type-II Weyl semimetal in the realistic ${\mathrm{YbMnBi}}_2$. Our work provides an insight into the realizations of the type-II Weyl state in antiferromagnetic topological materials.

We present a computationally efficient strategy that allows us to simulate magnetization switching driven by spin-transfer torque in magnetic tunnel junctions within a micromagnetic model coupled with a matrix-based nonequilibrium Green's function algorithm. Exemplary simulations for a realistic set of parameters are carried out and show switching times below $4\text{ns}$ for voltages above $300\text{mV}$ or around $2\times {10}^{10}\text{A}{\text{m}}^{-2}$ for the $\text{P}\to \text{AP}$ (parallel-to-antiparallel) direction. For $\text{AP}\to \text{P}$ switching, a trend reversal in the switching time is seen, i.e., the time for magnetization reversal first decreases with increasing bias voltage but then starts to rise again.

We utilize the concept of a measurement-induced entanglement transition to analyze the interplay and competition of processes that generate and destroy entanglement in a one-dimensional quantum spin chain evolving under a locally noisy and disordered Hamiltonian. We employ continuous measurements of variable strength to induce a transition from volume to area-law scaling of the steady-state entanglement entropy. While static background disorder systematically reduces the critical measurement strength, this critical value depends nonmonotonically on the strength of nonstatic noise. According to the extracted finite-size scaling exponents, the universality class of the transition is independent of the noise and disorder strength. We interpret the results in terms of the effect of static and nonstatic disorder on the intricate dynamics of the entanglement generation rate due to the Hamiltonian in the absence of measurement, which is fully reflected in the behavior of the critical measurement strength. Our results establish a firm connection between this entanglement growth and the steady-state behavior of the measurement-controlled systems, which therefore can serve as a tool to quantify and investigate features of transient entanglement dynamics in complex many-body systems via a steady-state phase transition.

The hyperfine interaction between the spins of electrons and nuclei is both a blessing and a curse. It can provide a wealth of information when used as an experimental probing technique but it can also be destructive when it acts as a dephasive perturbation on the electronic system. In this paper, we fabricated large-scale single and multilayer isotopically purified ${}^{13}\mathrm{C}$ graphene Hall bars to search for interaction effects between the nuclear magnetic moments and the electronic system. We find signatures of nuclei with a spin in the analysis of the weak localization phenomenon that shows a significant dichotomy in the scattering times of monolayer ${}^{12}\mathrm{C}$ and ${}^{13}\mathrm{C}$ graphene close to the Dirac point. Microwave-induced electron spin flips were exploited to transfer momentum to the nuclei and build-up a nuclear field. The presence of a very weak nuclear field is encoded in a modulation of the electron Zeeman energy which shifts the energy for resonant absorption and reduces the $g$ factor.

We study the temperature relaxation dynamics of nodal-line semimetals after a sudden excitation in the presence of acoustic and optical phonon modes. We find that the nodal line constrains the electron momenta in scattering processes, and as a result, the temperature relaxation due to acoustic phonons is exponential as a function of time. However, depending on initial conditions, other functional forms are possible. In typical pump-probe experiments, the temperature relaxation is linear due to acoustic phonons with rates that vary as $\sim n^{1/2}$ with density. The temperature relaxation due to optical phonons is also linear with rates $\sim n^{-1/2}$ or $\sim n$.

$S=\frac{1}{2}$ Ising kagome antiferromagnets (KAFs) are rare in reality. In this paper, we report the magnetic ground state and field-induced transitions of an $S=\frac{1}{2}$ Ising antiferromagnet with a stacked kagome geometry, ${\mathrm{Na}}_5{\mathrm{Co}}_{15.5}{\mathrm{Te}}_6{\mathrm{O}}_{36}$. Upon cooling, magnetic susceptibility measurements reveal three successive magnetic transitions at $T_1$ = 45.2 K, $T_2$ = 35.4 K, and $T_3\sim$ 20 K. When the magnetic field is applied along the Ising $c$ axis, a strikingly anomalous initial magnetization lying outside the hysteresis loop is observed below $T_3$. Through detailed characterizations, the magnetic field vs temperature phase diagram is established. A partially disordered antiferromagnetic state is proposed below $T_1$, which becomes frozen below $T_3$. ${\mathrm{Na}}_5{\mathrm{Co}}_{15.5}{\mathrm{Te}}_6{\mathrm{O}}_{36}$ is therefore a promising candidate for $S=\frac{1}{2}$ Ising KAFs, and this unique composite structure may shed light on the exploratory path for $S=\frac{1}{2}$ Ising KAFs.

We investigated current-induced torques in a single permalloy layer connected to nonmagnetic electrodes with lateral inversion asymmetry by spin-torque ferromagnetic resonance. Considering the symmetry of the spin-torque ferromagnetic resonance spectrum with respect to the magnetic field direction, we successfully separated various types of torque. In addition to in-plane damping-like and field-like torques, we detected two additional components of out-of-plane (OOP) torques, the symmetries of which with respect to the magnetic field direction correspond to an OOP field-like torque and an OOP damping-like torque. We obtained the OOP torques in particular by breaking a lateral inversion symmetry of the nonmagnetic electrodes, and the sign of the torques is reversed by inverting the electrode structure. The microwave frequency dependence of the OOP torques indicates that the OOP torques are not attributable to a spin current but to the Oersted field generated by a nonuniform charge current, $B_{\mathrm{Oersted}}$, and an inductive field, $B_{\mathrm{induc}.}$ (which originates from $B_{\mathrm{Oersted}}$). We propose an external field-free and fast magnetization switching of a ferromagnetic layer with perpendicular magnetic anisotropy by using $B_{\mathrm{induc}.}$, which can be achieved only by fabricating the electrodes asymmetrically.

We construct a single-particle Green function, which can identify topological phases of interacting systems. The Green function is defined by an effective Bloch Hamiltonian, which is equal to the inverse of the full Green function of interacting particles at zero frequency. Topological phases of interacting systems can be detected by the coincidence of the poles and the zeros of the diagonal components of the constructed Green function. The crosses of the zeros in the momentum space are also a signal of nontrivial topological phases. As a demonstration, we identify the topological phases in a minimal model of magnetic insulators. The model describes the double exchange process between itinerant electrons and magnetic moments in the presence of the spin-orbital coupling and the ionic potential of the itinerant electrons. The identification of topological phases by the zero's crosses is consistent with the topological invariant. We also found an antiferromagnetic state with topologically breaking of the spin symmetry, where electrons with one spin orientation are in topological insulating state, while electrons with the opposite spin orientation are in topologically trivial one.

We have investigated the effect of Cu substitution in ${\mathrm{Eu}}_2{\left({\mathrm{Ir}}_{1-x}{\mathrm{Cu}}_x\right)}_2{\mathrm{O}}_7$ with the help of magnetic and transport property measurements. XPS measurement reveals that each ${\mathrm{Cu}}^{2+}$ converts ${\mathrm{Ir}}^{4+}$ to double the amount of ${\mathrm{Ir}}^{5+}$ ions. The metal-insulator transition temperature ($T_{\text{MI}}$) is obtained around 120 K. In the insulating phase, at lower temperature below 50 K, the temperature-dependent resistivity follows a power-law dependence and the magnitude of the exponent increases with Cu concentrations. The temperature-dependent thermopower is observed to follow the electrical resistivity down to 50 K, except for a sudden drop in thermopower at temperature below 50 K. We find negligible Hall voltage in the metallic regime of the samples but a sudden Hall voltage is developed below 50 K. We observe bifurcation in zero-field-cooled and field-cooled (ZFC-FC) magnetization below irreversibility temperature, exchange bias, and negative magnetoresistance at 3 K and the magnitude of all these properties increases with Cu concentrations. In the insulating region (below 6 K) there exists a linear specific heat and its coefficient decreases with Cu doping, which indicates the reduction of spinon contribution with Cu doping.

${\mathrm{Co}}_{1/3}{\mathrm{NbS}}_2$ is the magnetic intercalate of 2H-${\mathrm{NbS}}_2$ where electronic itinerant and magnetic properties strongly influence each other throughout the phase diagram. Here we report the angle-resolved photoelectron spectroscopy (ARPES) study in ${\mathrm{Co}}_{1/3}{\mathrm{NbS}}_2$. In agreement with previous reports, the observed electronic structure seemingly resembles the one of the parent material 2H-${\mathrm{NbS}}_2$, with the shift in Fermi energy of 0.5 eV accounting for the charge transfer of approximately two electrons from each Co ion into the ${\mathrm{NbS}}_2$ layers. However, in addition, and in contrast to previous reports, we observe significant departures that cannot be explained by the rigid band shift accompanied by minor deformation of bands: First, entirely unrelated to the 2H-${\mathrm{NbS}}_2$ electronic structure, a shallow electronic band is found crossing the Fermi level near the boundary of the first Brillouin zone of ${\mathrm{Co}}_{1/3}{\mathrm{NbS}}_2$. The evolution of the experimental spectra upon varying the incident photon energy suggests the Co origin of this band. Second, the Nb bonding band, found deeply submerged below the Fermi level at the $\mathrm{\Gamma }$ point, indicates that the interlayer hybridization is significantly amplified by intercalation, with Co magnetic ions probably acting as strong covalent bridges between ${\mathrm{NbS}}_2$ layers. The strong hybridization between orbitals that support the itinerant states and the orbitals hosting the local magnetic moments indicates the importance of strong electronic correlations, with the interlayer coupling playing an exquisite role.

We present theoretical calculations for the cyclotron resonance and various magnetoplasmon modes of a Coulomb interacting two-dimensional GaAs electron gas (2DEG) modulated as a lateral superlattice of quantum dots subjected to an external perpendicular constant magnetic field. We use a real-time excitation approach based on the Liouville–von Neumann equation for the density operator, that can go beyond linear response delivering information of all longitudinal and transverse collective modes of interest to the same order. We perform an extensive analysis of the coexisting collective modes due to the lateral confinement and the magnetic field for a different number of electrons in each dot. In the limit of vanishing dot modulation of the 2DEG we find signs of the structure of the Hofstadter butterfly in the excitation spectra.

We numerically study the tuning of the radiative heat transfer between a spherical InSb nanoparticle in the vicinity of a flat SiC surface assisted by a static magnetic field. By changing the value of the applied magnetic field, the dielectric function of the nanosphere becomes anisotropic due to the excitation of magnetoplasmons. In the dipolar approximation, the plasmon resonance of the particle splits into two additional satellite resonances that shift to higher and lower frequencies as the field increases. When one of the particle resonances overlaps with the phonon-polariton frequency of the SiC surface, an enhancement of the heat transfer of two orders of magnitude is obtained. To understand the tuning of the radiative heat transfer, we present a detailed analysis of the nature of the modes that can be excited (surface, bulk, and hyperbolic).