The lattice thermal conductivity of layered group 4 disulfides ${\mathrm{TiS}}_2$, ${\mathrm{ZrS}}_2$, and ${\mathrm{HfS}}_2$ has been studied using dispersion-corrected hybrid density functional methods. Results obtained using both relaxation time approximation (RTA) and full solution of linearized Boltzmann transport equation have been compared and rigorously analyzed. The periodic trends of lattice thermal conductivity and its components are investigated in detail. The in-plane RTA lattice thermal conductivities of ${\mathrm{TiS}}_2$, ${\mathrm{ZrS}}_2$, and ${\mathrm{HfS}}_2$ at 300 K are 6.1, 8.5, and $11.7\mathrm{W}{\mathrm{m}}^{-1}{\mathrm{K}}^{-1}$, respectively. In the cross-plane direction, where the metal sulfide layers are kept together by weak van der Waals interactions, the RTA lattice thermal conductivities of ${\mathrm{TiS}}_2$, ${\mathrm{ZrS}}_2$, and ${\mathrm{HfS}}_2$ at 300 K are 1.4, 1.4, and $2.0\mathrm{W}{\mathrm{m}}^{-1}{\mathrm{K}}^{-1}$, respectively.

The ultrafast demagnetization (UFD) dynamics of itinerant ferromagnets is theoretically investigated as a function of the characteristics of the initial laser excitation. A many-body $pd$-band Hamiltonian is considered which takes into account hybridizations, Coulomb interactions, spin-orbit interactions, and the coupling to the laser field on the same electronic level. In this way, a fruitful connection is established between the nonadiabatic quantum dynamics and the well-known equilibrium statistical mechanics of itinerant-electron ferromagnets. The time evolution during and after the pulse absorption is determined exactly by performing numerical Lanczos propagations on a small cluster model with parameters appropriate for Ni. The most relevant laser parameters, namely, the fluence $F$, wave length $\lambda$, polarization $\widehat{\varepsilon }$, and pulse duration ${\tau }_p$ are varied systematically. The results show how $F$, $\widehat{\varepsilon }$, and ${\tau }_p$ allow one to control the total absorbed energy, the spectral distribution of the initial excitation, and the subsequent magnetization dynamics. The calculations show that reasonable changes in these parameters do not affect the UFD dynamics qualitatively and have only a minor influence on the timescale ${\tau }_{\text{dm}}$ which characterizes the initial demagnetization. In contrast, our model predicts that the degree of demagnetization $\mathrm{\Delta }{S}_z/S_z^0$ achieved for $t\gtrsim {\tau }_{\text{dm}}$ correlates well with the average number of electrons excited by the laser or average number of absorbed photons $n_{\text{ph}}$, which can be tuned by varying the fluence, spectral distribution and polarization of the laser pulse. The theoretical results are discussed by comparing them with available experiments. From a fundamental perspective, the robustness of the ultrafast demagnetization effect is theoretically demonstrated, as a phenomenon reflecting the intrinsic dynamics of the metallic $3d$ valence electrons. A wide variety of well-focused possibilities of tailoring the efficacy of the ultrafast demagnetization process is thereby opened.

A nonstationary anomalous Hall current is calculated for a voltage biased Josephson junction, which is composed of two $s$-wave superconducting contacts deposited on the top of a three-dimensional topological insulator (TI). A homogeneous Zeeman field was assumed at the surface of the TI. The problem has been considered within the ballistic approximation and on the assumption that tunneling of electrons between contacts and the surface of the TI is weak. In this regime the Josephson current has no features of the $4\pi$-periodic topological effect which is associated with Andreev bound states. It is shown that the Hall current oscillates in time. The phase of these oscillations is shifted by $\pi /2$ with respect to the Josephson current and their amplitude linearly decreases with the electric potential difference between contacts. It is also shown that the Hall current cannot be induced by a stationary phase difference of the contact's order parameters.

We study quantum quenches in the $S=1$ Heisenberg spin chain and show that the dynamics can be described by the recently developed semi-semiclassical method based on particles propagating along classical trajectories but scattering quantum mechanically. We analyze the nonequilibrium time evolution of the distribution of the total spin in half of the system and compare the predictions of the semi-semiclassical theory with those of a non-Abelian time-evolving block decimation (TEBD) algorithm which exploits the SU(2) symmetry. We show that while the standard semiclassical approach using the universal low-energy scattering matrix cannot describe the dynamics, the hybrid semiclassical method based on the full scattering matrix gives excellent agreement with the first-principles TEBD simulation.

We investigate theoretically the interplay of proximity effects due to the presence of a superconductor and normal ferromagnetic leads on the formation of the spintronic quadrupolar exchange field in a large-spin molecule. We show that the spintronic anisotropy can be enhanced by a few orders of magnitude and tuned by changing the strength of coupling to the superconductor. Especially large anisotropy is generated in the vicinity of the charge parity changing transition of the molecule. We also provide predictions of measurable spectral properties being the hallmarks of these phenomena.

Exchange-correlation (XC) thermal effects for transport and optical properties of deuterium along the principal Hugoniot are investigated. The study is performed using ab initio molecular dynamics simulations within the Mermin-Kohn-Sham density functional theory. XC thermal effects are taken into account via the temperature-dependent Karasiev-Dufty-Trickey generalized gradient approximation functional [V. V. Karasiev et al., Phys. Rev. Lett. 120, 076401 (2018)]. We find that XC thermal effects account for the softening of the Hugoniot at pressures $P>250$ GPa and improve agreement with recent experimental measurements. Also, XC thermal effects lead to the reflectivity increase by about 2% for shock speeds above 20 km/s. The calculated reflectivity for shock speeds up to 50 km/s is in excellent agreement with recent experimental measurements on the Omega Laser System. The dc conductivity is increased by about 4% due to XC thermal effects. The system evolution along the Hugoniot crosses the so-called warm-dense-matter regime, and XC thermal effects must be taken into account to accurately predict the thermophysical properties across warm-dense conditions.

In this work we use fluorescence from nitrogen-vacancy defects in diamond to detect and explore other paramagnetic defects in the diamond, such as P1 defects, which are not commonly detectable through optical detection of magnetic resonance in standard conditions. Our method does not require overlap between the defects' resonances and therefore is applicable in a large region of magnetic fields and frequencies, as verified by excellent fit to theoretical predictions. We propose a depolarization scheme of P1 defects to account for the observed data. To verify our results, we perform cavity-based detection of magnetic resonance and find a good agreement between the measured optically induced polarization and the value obtained theoretically from rate equations. The findings in this work may open the way to detection of paramagnetic defects outside of the diamond through the photoluminescence of nitrogen-vacancy defects, which might be useful for imaging in biology.

${\mathrm{Rb}}_2{\mathrm{Cu}}_2{\mathrm{Mo}}_3{\mathrm{O}}_{12}$ is a quasi-one-dimensional frustrated $S=1/2$ multiferroic that displays magnetic field-tunable ferroelectricity with no long-range magnetic order. To interrogate this intriguing behavior we employed dielectric measurements, neutron diffraction, and muon spin spectroscopy to study powder samples at mK temperatures and tesla magnetic fields. Subtle signatures in the experimental data allow the identification of different dielectric and magnetic regimes, none of which conclusively suggest the existence of magnetic long-range order. The results are broadly consistent with the system hosting a gapped nonmagnetic ground state in zero field, that undergoes a magnetic field-induced transition at $\sim 2$ T into a phase with a static, disordered spin arrangement. We discuss our results in the context of previous work on this system, and conclude that the origin of a magnetic field-dependent electric polarization with no long-range magnetic order could call for a new paradigm of magnetically driven ferroelectricity.

We investigate spin-orbit torques on magnetization in an insulating ferromagnetic layer that is brought into close proximity to a topological insulator (TI). In addition to the well-known fieldlike spin-orbit torque, we identify an anisotropic anti-damping-like spin-orbit torque that originates in a diffusive motion of conduction electrons. This diffusive torque is vanishing in the limit of zero momentum (i.e., for a spatially homogeneous electric field or current), but it may, nevertheless, have a strong impact on spin-torque resonance at finite frequency provided the external field is neither parallel nor perpendicular to the TI surface. The required electric-field configuration can be created by a grated top gate.

We present detailed inelastic neutron scattering measurements of the noncollinear antiferromagnet ${\mathrm{Mn}}_3\mathrm{Ge}$. Time-of-flight and triple-axis spectroscopy experiments were conducted at the temperature of 6 K, well below the high magnetic ordering temperature of 370 K. The magnetic excitations have a 5-meV gap and display an anisotropic dispersive mode reaching $\sim 90$ meV at the boundaries of the magnetic Brillouin zone. The spectrum at the zone center shows two additional excitations that demonstrate characteristics of both magnons and phonons. Ab initio lattice-dynamics calculations show that these can be associated with the magnon-polaron modes resulting from the hybridization of the spin fluctuations and the low-energy optical phonons. The observed magnetoelastic coupling agrees with the previously found negative thermal expansion in this compound and resembles the features reported in the spectroscopic studies of other antiferromagnets with similar noncollinear spin structures.

This article shows that the spin-to-charge current conversion in single-layer graphene (SLG) by means of the inverse Rashba-Edelstein effect (IREE) is made possible with the integration of this remarkable 2D material with the unique ferrimagnetic insulator yttrium iron garnet ($\mathrm{YIG}={\mathrm{Y}}_3\mathrm{F}{\mathrm{e}}_5{\mathrm{O}}_{12}$) as well as with the ferromagnetic metal permalloy ($\mathrm{Py}=\mathrm{N}{\mathrm{i}}_{81}\mathrm{F}{\mathrm{e}}_{19}$). By means of x-ray absorption spectroscopy and magnetic circular dichroism techniques, we show an induced magnetic moment in carbon atoms of the SLG due to the proximity effect with the magnetic layer. The spin currents are generated in the magnetic layer by spin pumping from microwave-driven ferromagnetic resonance and are detected by a dc voltage along the graphene layer, at room temperature. The spin-to-charge current conversion, occurring at the graphene layer, is explained by the extrinsic spin-orbit interaction induced by the proximity effect with the ferromagnetic layer. The results obtained for the SLG/YIG and SLG/Py systems confirm very similar values for the IREE parameter, which are larger than the values reported in previous studies for SLG. We also report systematic investigations of the electronic and magnetic properties of SLG/YIG by means of scanning tunneling microscopy.

Exerting control over the magnetic exchange interaction in heterostructures is of both basic interest and has potential for use in spin-based applications relying on quantum effects. We show that the sign of the exchange interaction in a spin valve, determining whether a parallel (p) or antiparallel (ap) magnetic configuration is favored, can be controlled via an electric voltage. This occurs due to an interplay between a nonequilibrium quasiparticle distribution and the presence of spin-polarized Cooper pairs. Additionally, we show that a voltage-induced distribution controls the anomalous supercurrent that occurs in magnetic Josephson junctions, obviating the challenging task to manipulate the magnetic texture of the system. This demonstrates that two key phenomena in superconducting spintronics, the magnetic exchange interaction and the phase shift generating the anomalous Josephson effect, can be controlled electrically. Our findings are of relevance for spin-based superconducting devices which in practice likely have to be operated precisely by nonequilibrium effects.

We investigate the dynamics of hybrid junctions made of the topological superconductor (TS) and normal metal (N) wires. We consider an X-Y-Z configuration for the junctions where X, Y, Z = TS, N. We assume the wires X and Z are semi-infinite and in thermal equilibrium. We connect the wires X and Z through the short Y wire at some time and numerically study time evolution of the full device. For TS-N-TS devices, we find a persistent, oscillating electrical current at both junctions even in the absence of any phase, voltage, or thermal bias. The amplitude and period of the oscillating current depend on the initial conditions of the middle N wire indicating the absence of thermalization. This zero-bias current vanishes at long times for any of X and Z being an N wire or a TS wire near a topological phase transition. Using properties of different bound states within the superconducting gap, we develop a clear understanding of the oscillating currents.

The spin-filter material CrVTiAl is a promising candidate for producing highly spin-polarized currents at room temperature in a nonmagnetic architecture. Thin films of compensated-ferrimagnetic CrVTiAl have been grown, and their electrical and magnetic properties have been studied. The resistivity shows two-channel semiconducting behavior with one disordered gapless channel and a gapped channel with activation energy $\mathrm{\Delta }E=0.1–0.2$ eV. Magnetoresistance measurements to $B=35$ T provide values for the mobilities of the gapless channel, leading to an order of magnitude difference in the carrier effective masses, which are in reasonable accord with our density-functional-theory-based results. The density of states and electronic band structure are computed for permutations of the four sublattices arranged differently along the (111) body diagonal, yielding metallic (Cr-V-Al-Ti), spin-gapless (Cr-V-Ti-Al), and spin-filtering (Cr-Ti-V-Al) phases. Robustness of the spin-gapless phase to substitutional disorder is also considered.

Motivated by the constrained many-body dynamics, the stability of the localization-delocalization properties to the inclusion of soft constraints is addressed in random matrix models. These constraints are modeled by correlations in long-ranged hopping with the Pearson correlation coefficient different from zero or unity. Counterintuitive robustness of delocalized phases, both ergodic and (multi)fractal, in these models, is numerically observed and confirmed by the analytical calculations. First, the matrix inversion trick is used to uncover the origin of such robustness. Next, to characterize delocalized phases, a method of eigenstate calculation, sensitive to correlations in long-ranged hopping terms, is developed for random matrix models and approved by numerical calculations and the previous analytical ansatz. The effect of the robustness of states in the bulk of the spectrum to the inclusion of soft constraints is generally discussed for single-particle and many-body systems.

We investigate Anderson transitions for a system of two particles moving in a three-dimensional disordered lattice and subject to on-site (Hubbard) interactions of strength $U$. The two-body problem is exactly mapped into an effective single-particle equation for the center-of-mass motion, whose localization properties are studied numerically. We show that, for zero total energy of the pair, the transition occurs in a regime where all single-particle states are localized. In particular, the critical disorder strength exhibits a nonmonotonic behavior as a function of $\left|U\right|$, increasing sharply for weak interactions and converging to a finite value in the strong-coupling limit. Within our numerical accuracy, short-range interactions do not affect the universality class of the transition.

We study a quantum Ising chain with tailored bulk dissipation, which can be mapped onto a non-Hermitian Ashkin-Teller model. By exploiting the Kohmoto-den Nijs-Kadanoff transformation, we further map it to a staggered XXZ spin chain with pure-imaginary anisotropy parameters. This allows us to study the eigenstates of the original Liouvillian in great detail. We show that the steady state in each parity sector is a completely mixed state. The uniqueness of each is proved rigorously. We then study the decay modes on the self-dual line corresponding to the uniform XXZ chain and obtain an exact formula for the Liouvillian gap $g$, the inverse relaxation time, in the thermodynamic limit. The gap $g$ as a function of dissipation strength $\mathrm{\Delta }$ has a cusp, implying a kind of phase transition for the first decay mode.