We show that a current sweep along the $IV$ curve of the ${\phi }_0$ junction may lead to regular magnetization dynamics with a series of specific phase trajectories. The origin of these trajectories is related to a direct coupling between the magnetic moment and the Josephson oscillations in these junctions and ferromagnetic resonance when Josephson frequency coincides with the ferromagnetic one. We demonstrate that an external electromagnetic field can control the dynamics of magnetic moment within a current interval corresponding to a Shapiro step and produce a specific transformation of precession trajectories. As an effect of the coupling between magnetization and spin-orbit interaction, we demonstrate the appearance of the dc component of superconducting current and clarify its role in the transformation of $IV$ characteristics in the resonance region. Good agreement between numerical and analytical results has been found in the ferromagnetic resonance region. The presented results might be used for developing novel resonance methods of determination of the spin-orbit coupling parameter in noncentrosymmetric materials. We discuss experiments which can test our results.

In this paper, we study a two-band model of a superconductor in a square lattice. One band is narrow in energy and includes local Coulomb correlations between its quasiparticles. Pairing occurs in this band due to nearest-neighbor attractive interactions. Extended $s$-wave as well as $d$-wave symmetries of the superconducting order parameter are considered. The correlated electrons hybridize with those in another wide conduction band through a $k$-dependent mixing with even or odd parity depending on the nature of the orbitals. The many-body problem is treated within a slave-boson approach that has proved adequate to deal with the strong electronic correlations that are assumed here. Since applied pressure changes mostly the ratio between hybridization and bandwidths, we can use this ratio as a control parameter to obtain the phase diagrams of the model. We find that, for a wide range of parameters, the critical temperature increases as a function of hybridization (pressure) with a region of first-order transitions. When frustration is introduced, it gives rise to a stable superconducting phase. We find that superconductivity can be suppressed for specific values of band filling due to the Coulomb repulsion. We show how pressure, composition, and strength of correlations affect the superconductivity for different symmetries of the order parameter and the hybridization.

We construct the most generic Hamiltonian of the $8Pmmn$ structure of a borophene sheet in the presence of spin orbit, as well as background electric and magnetic fields. In addition to spin and valley Hall effects, this structure offers a framework to conveniently manipulate the resulting “tilt” of the Dirac equation by applying appropriate electric fields. Therefore, the tilt can be made space as well as time dependent. The border separating the low-field region with undertilted Dirac fermions from the high-field region with over-tilted Dirac fermions will correspond to a black-hole horizon. In this way, space-time-dependent electric fields can be used to design the metric of the resulting space-time felt by electrons and holes satisfying the tilted Dirac equation. Given that the velocity of light is replaced by a two to three orders-of-magnitude smaller Fermi velocity, the tests of gravity when imported to our solid-state setting will correspond to four to six orders-of-magnitude larger effects. Our platform offers a way to generate analogues of (nonpropagating) gravitational waves by electric fields (rather than by mass sources) which can be detected in solid-state spectroscopies as enhanced superconducting correlations.

We report on a high-resolution optical and magneto-optical spectroscopy, luminescence, and electron paramagnetic resonance (EPR) studies of yttrium orthophosphate single crystals doped with erbium, which are promising telecom-wavelength materials for applications in quantum electronics and quantum information processing. An observation of the hyperfine structure in optical spectra of ${}^{167}\mathrm{Er}$ isotope in ${\mathrm{Er}:\mathrm{YPO}}_4$ is presented. Energies and symmetries of 40 crystal-field levels of ${\mathrm{Er}}^{3+}$ in ${\mathrm{Er}:\mathrm{YPO}}_4$ and $g$ factors of some of them were determined and successfully modeled on the basis of crystal-field calculations. The obtained set of crystal-field parameters was used in modeling the hyperfine structure observed in the optical and EPR spectra of ${\mathrm{Er}:\mathrm{YPO}}_4$ single crystals.

Performing Monte Carlo simulations, we study the temperature-dependent self-organization of magnetic moments coupled to itinerant electrons in a finite-size one-dimensional nanostructure proximitized to a superconducting reservoir. At low temperatures, an effective interaction between the localized magnetic moments, that is mediated by itinerant electrons, leads to their helical ordering. This ordering, in turn, affects the itinerant electrons, inducing the topologically nontrivial superconducting phase that hosts the Majorana modes. In a wide range of system parameters, the spatial periodicity of a spiral order that minimizes the ground-state energy turns out to promote the topological phase. We determine the correlation length of such spiral order and study how it is reduced by thermal fluctuations. This reduction is accompanied by suppression of the topological gap (which separates the zero-energy mode from continuum), setting the upper (critical) temperature for the existence of the Majorana quasiparticles. Monte Carlo simulations do not rely on any ansatz for configurations of the localized moments, therefore, they can be performed for arbitrary model parameters, also beyond the perturbative regime.

Electron-hole pairs can be excited coherently in a quantum conductor by applying voltage pulses to its contact. We find that these electron-hole pairs can be classified into two kinds, whose excitation probabilities have different dependences on the Faraday flux of the pulse. Most of the pairs are of the first kind, which can be referred to as “normal” pairs. Their excitation probabilities increase nearly monotonically with the flux and saturate to the maximum value of 1 when the flux is large enough. In contrast, there exist “anomalous” pairs, whose excitation probabilities can exhibit oscillations with the flux. These pairs can be excited by only pulses with a small width. Due to the oscillation of the probabilities, the anomalous pairs can lead to different features in the full counting statistics of the electron-hole pairs for pulses with integer and noninteger fluxes.

We generalize the construction of the spin-1/2 SU(2) resonating valence bond (RVB) state to the case of the self-conjugate $\mathbf{6}$ representation of SU(4). As for the case of SU(2) [J.-Y. Chen and D. Poilblanc, Phys. Rev. B 97, 161107(R) (2018)], we use the projected entangled pair state (PEPS) formalism to derive a simple (two-dimensional) family of generalized SU(4) RVB states on the square lattice. We show that, when longer-range SU(4)-singlet bonds are included, a local gauge symmetry is broken down from U(1) to ${\mathbb{Z}}_2$, leading to the emergence of a short-range spin liquid. Evidence for the topological nature of this spin liquid is provided by the investigation of the Renyi entanglement entropy of infinitely long cylinders and of the modular matrices. Relevance to microscopic models and experiments of ultracold atoms is discussed.

An electromagnetic plasma mode has been discovered in the hybrid system formed by a highly conductive gate strip placed in proximity to the two-dimensional electron system. The plasmon mode propagates along the gate strip with no potential nodes present in transverse direction. Its spectrum combines characteristic features of both gated and ungated two-dimensional plasmons. The plasma excitation has been found to exhibit anomalously strong interaction with light.

Materials with the ideal case of a single pair of Weyl points (WPs) are highly desirable for elucidating the unique properties of Weyl fermions. $\mathrm{EuC}{\mathrm{d}}_2\mathrm{A}{\mathrm{s}}_2$ is an antiferromagnetic topological insulator or Dirac semimetal depending on the different magnetic configurations. Using first-principles band-structure calculations, we show that inducing ferromagnetism in $\mathrm{EuC}{\mathrm{d}}_2\mathrm{A}{\mathrm{s}}_2$ can generate a single pair of WPs from splitting the single pair of antiferromagnetic Dirac points due to its half-metallic nature. Analysis with a low-energy effective Hamiltonian shows that a single pair of WPs is obtained in $\mathrm{EuC}{\mathrm{d}}_2\mathrm{A}{\mathrm{s}}_2$ because the Dirac points are very close to the zone center and the ferromagnetic exchange splitting is large enough to push one pair of WPs to merge and annihilate at Γ while the other pair survives. Furthermore, we predict that alloying with Ba at the Eu site can stabilize the ferromagnetic configuration and generate a single pair of Weyl points without application of a magnetic field.

The Kondo insulator compound $\mathrm{Sm}{\mathrm{B}}_6$ has emerged as a strong candidate for the realization of a topologically nontrivial state in a strongly correlated system, a topological Kondo insulator, which can be a novel platform for investigating the interplay between nontrivial topology and emergent correlation-driven phenomena in solid-state systems. Electronic transport measurements on this material, however, so far showed only the robust surface-dominated charge conduction at low temperatures, lacking evidence of its connection to the topological nature by showing, for example, spin polarization due to spin-momentum locking. Here, we find evidence for surface-state spin polarization by electrical detection of a current-induced spin chemical-potential difference on the surface of a $\mathrm{Sm}{\mathrm{B}}_6$ single crystal. We clearly observe that a surface-dominated spin voltage, which is proportional to the projection of the spin polarization onto the contact magnetization, is determined by the direction and magnitude of the charge current and is strongly temperature dependent due to the crossover from surface to bulk conduction. We estimate the lower bound of the surface-state net spin polarization as 25% based on the quantum transport model, providing direct evidence that $\mathrm{Sm}{\mathrm{B}}_6$ supports metallic spin helical surface states.

An efficient basis set for products of all-electron wave functions is proposed, which comprises plane waves defined over the entire unit cell and orbitals confined to small nonoverlapping spheres. The size of the set and the basis functions are, in principle, independent of the computational parameters of the band-structure method. The approach is implemented in the extended linearized augmented plane wave method, and its properties and accuracy are discussed. The method is applied to analyze the dielectric response of the simple metals Al, Na, Li, K, Rb, and Cs with a focus on the origin of the anisotropy of the plasmon dispersion in Al and Na. The anisotropy is traced to tiny structures of the one-particle excitation spectra of Al and Na, and relevant experimental observations are explained.

The Mott insulator is the quintessential strongly correlated electronic state. We obtain complete insight into the physics of the two-dimensional Mott insulator by extending the slave-fermion (holon-doublon) description to finite temperatures. We first benchmark its predictions against state-of-the-art quantum Monte Carlo simulations, demonstrating quantitative agreement. Qualitatively, the short-ranged spin fluctuations both induce holon-doublon bound states and renormalize the charge sector to form the Hubbard bands. The Mott gap is understood as the charge gap renormalized downward by these spin fluctuations. As temperature increases, the Mott gap closes before the charge gap, causing a pseudogap regime to appear naturally during the melting of the Mott insulator.

The path from the charge density wave antiferromagnet ${\mathrm{NdNiC}}_2$ to the noncentrosymmetric superconductor ${\mathrm{LaNiC}}_2$ is studied by gradual replacement of Nd by La ions. The evolution of physical properties is explored by structural, magnetic, transport, magnetoresistance, and specific heat measurements. With the substitution of La for Nd, the Peierls temperature is gradually suppressed, which falls within the BCS mean-field relation for chemical pressure with a critical concentration of $x_c=0.38$. As long as the charge density wave (CDW) is maintained, the antiferromagnetic (AFM) ground state remains robust against doping and, despite a Néel temperature reduction, shows a rapid and sharp magnetic transition. Once the CDW is completely suppressed, intermediate compounds of the ${\mathrm{Nd}}_{1-x}{\mathrm{La}}_x{\mathrm{NiC}}_2$ series reveal symptoms of a gradual softening of the features associated with the AFM transition and an increase of the spin disorder. Immediately after the antiferromagnetic transition is depressed to zero temperature, the further incorporation of La ions results in the emergence of superconductivity. This crossover in ${\mathrm{Nd}}_{1-x}{\mathrm{La}}_x{\mathrm{NiC}}_2$ is discussed in terms of the possible quantum critical point.

The magnetic phase diagram of Cr(dien)$\left({\mathrm{O}}_2{)}_2·{\mathrm{H}}_2\mathrm{O}(\text{dien}={\mathrm{C}}_4{\mathrm{H}}_{13}{\mathrm{N}}_3\right)$, a quasi-two-dimensional spin-1 antiferromagnet known to exhibit quantum phase behavior, is reported. Specific heat, torque magnetometry, and magnetocalorimetry were employed to obtain the phase diagram down to 200 mK. Near the $T\to 0$ limit, the antiferromagnetic phase defers to a field-induced ferromagnetic phase at a critical field $H_C$. Analysis of the phase boundary through fitting with $\left(H-H_C\right)=\beta T^{\alpha }$ yielded $H_C$ and the critical exponent $\alpha$ of the spin system. $H_C$ and $\alpha$ were found to be $15.2\pm 0.02$ T and $2.05\pm 0.09$, respectively, when $\mathit{H}$ is parallel to the easy magnetic axis, and $12.4\pm 0.01$ T and $1.91\pm 0.06$ when perpendicular to it. These critical exponents are indicative of an Ising-type spin system, which was an unanticipated result. Furthermore, torque magnetometry detected a spin-flop transition over a wide orientation range of nearly 70° in the $ab$ plane. Mean field theory yielded an estimate of the long sought-after single-ion anisotropy for this compound, $D\approx 0.25$ K.

Two-dimensional (2D) van der Waals (vdW) materials have attracted significant attention for their promising applications in spintronic devices. Here, using first-principles calculations and renormalized spin-wave theory, we investigate the influence of surface adsorption (H and alkali metals) on the bandgap and ferromagnetism of monolayer ${\mathrm{Cr}}_2{\mathrm{Ge}}_2{\mathrm{Te}}_6$. We find that H-atom adsorption maintains the bandgap of ${\mathrm{Cr}}_2{\mathrm{Ge}}_2{\mathrm{Te}}_6$ around 0.95 eV but leads to a nearly indirect-to-direct band gap transition, while alkali-metal adsorption removes the bandgap and induces metallicity. More importantly, both H and alkali-metal adsorption surprisingly make the magnetic anisotropy energy four times larger than that of pristine ${\mathrm{Cr}}_2{\mathrm{Ge}}_2{\mathrm{Te}}_6$, leading to an increase of $T_{\mathrm{c}}$ by about 33%. Our findings of adsorption-controlled bandgap and magnetism in a 2D vdW magnet may open up opportunities for potential applications for new-generation magnetic memory storage, sensors, and spintronics.

In this work, we derive the Landau-Lifshitz-Bloch equation accounting for the multidomain antiferromagnetic (AFM) lattice at finite temperature, in order to investigate the domain wall motion, the core issue for AFM spintronics. The continuity equation of the staggered magnetization is obtained using the continuum approximation, allowing an analytical calculation of the domain wall dynamics. The influence of temperature on the static domain wall profile is investigated, and the analytical calculations agree well with the numerical simulations on temperature-gradient-driven domain wall motion, confirming the validity of this theory. Furthermore, the decrease of the acceleration and the increase of the saturation velocity of the domain wall with the increase of temperature are uncovered for a fixed gradient. Moreover, it is worth noting that this theory could be also applied to dynamics of various wall motions in an AFM system. The present theory represents a comprehensive approach to the domain wall dynamics in AFM materials, a crucial step toward the development of AFM spintronics.