We calculate the radiative heat transfer between two identical metallic one-dimensional lamellar gratings. To this aim we present and exploit a modification to the widely used Fourier modal method, known as adaptive spatial resolution, based on a stretch of the coordinate associated with the periodicity of the grating. We first show that this technique dramatically improves the rate of convergence when calculating the heat flux, allowing us to explore smaller separations. We then present a study of heat flux as a function of the grating height, highlighting a remarkable amplification of the exchanged energy, ascribed to the appearance of spoof-plasmon modes, whose behavior is also spectrally investigated. Differently from previous works, our method allows us to explore a range of grating heights extending over several orders of magnitude. By comparing our results to recent studies we find a consistent quantitative disagreement with some previously obtained results going up to 50%. In some cases, this disagreement is explained in terms of an incorrect connection between the reflection operators of the two gratings.

The dynamical charge-density response of bulk bismuth has been studied within time-dependent density functional perturbation theory, explicitly accounting for spin-orbit coupling. The use of the Liouville–Lanczos approach allows us to calculate electron energy loss spectra for excitation energies as large as 100 eV. Effects of $5d$ semicore electronic states, spin-orbit coupling, exchange and correlation, local fields, and anisotropy are thoroughly investigated. The account of the $5d$ states in the calculation turns out to be crucial to correctly describe the loss spectra above 10 eV and, in particular, the position and shape of the bulk-plasmon peak at 14.0 eV at vanishing transferred momentum. Our calculations reveal the presence of interband transitions at 16.3 eV, which had never been discussed before. The origin of the peak at 5.8 eV is revisited as due to mixed interband and collective excitations. Finally, our study supplements the lack of experiments at finite transferred momenta.

The dynamics of entanglement has recently been realized as a useful probe in studying ergodicity and its breakdown in quantum many-body systems. In this paper, we study theoretically the growth of entanglement in quantum many-body systems and propose a method to measure it experimentally. We show that entanglement growth is related to the spreading of local operators in real space. We present a simple toy model for ergodic systems in which linear spreading of operators results in a universal, linear-in-time growth of entanglement for initial product states, in contrast with the logarithmic growth of entanglement in many-body localized (MBL) systems. Furthermore, we show that entanglement growth is directly related to the decay of the Loschmidt echo in a composite system comprised of several copies of the original system, in which connections are controlled by a quantum switch (two-level system). By measuring only the switch's dynamics, the growth of the Rényi entropies can be extracted. Our work provides a way of understanding entanglement dynamics in many-body systems and to directly measure its growth in time via a single local measurement.

We formulate a general microscopic approach to spin-orbit torques in thin ferromagnet/heavy-metal bilayers in linear response to electric current or electric field. The microscopic theory we develop avoids the notion of spin currents and spin-Hall effect. Instead, the torques are directly related to a local spin polarization of conduction electrons, which is computed from generalized Kubo-Středa formulas. A symmetry analysis provides a one-to-one correspondence between polarization susceptibility tensor components and different torque terms in the Landau-Lifshitz-Gilbert equation for magnetization dynamics. The spin-orbit torques arising from Rashba or Dresselhaus type of spin-orbit interaction are shown to have different symmetries. We analyze these spin-orbit torques microscopically for a generic electron model in the presence of an arbitrary smooth magnetic texture. For a model with spin-independent disorder we find a major cancellation of the torques. In this case the only remaining torque corresponds to the magnetization-independent Edelstein effect. Furthermore, our results are applied to analyze the dynamics of a skyrmion under the action of electric current.

The temperature-pressure phase diagram of ferromagnetic superconductor UCoGe includes four phase transitions. They are between the paramagnetic and the ferromagnetic states with the subsequent transition in the superconducting ferromagnetic state and between the normal and the superconducting states after which the transition to the superconducting ferromagnetic state has to occur. Here we have developed the Landau theory description of the phase diagram and established the specific ordering arising at each type of transition. The phase transitions to the ferromagnetic superconducting state are inevitably accompanied by the emergence of screening currents. The corresponding magnetostatics considerations allow for establishing the significant difference between the transition from the ferromagnetic to the ferromagnetic superconducting state and the transition from the superconducting to the ferromagnetic superconducting state.

We performed investigations of ensembles of molecular nitrogen nanoclusters, containing stabilized nitrogen atoms, immersed in liquid helium by electron spin resonance and optical spectroscopy. We observed thermoluminescence of nitrogen atoms and molecules via increasing temperature from 1.25 to 4.4 K. Two thermoluminescence maxima were observed, one in superfluid helium (HeII) at $T\sim 1.9$ K and another in normal helium (HeI) at $T\sim 3.2\mathrm{K}$. We explain appearance of luminescence in HeII by chemical reactions of nitrogen atoms on surfaces of nanoclusters which might be initiated by quantum vortices. Thermoluminescence in HeI occurs due to the process of nanocluster association resulting in thermal explosions of a small fraction of nanoclusters. This research might open new possibilities for studying a broad range of chemical reactions initiated by quantum vortices in HeII.

High transition temperature ($T_{\mathrm{c}}$) superconductivity in FeSe/$\mathrm{SrTi}{\mathrm{O}}_3$ has been widely discussed on the possible mechanisms in conjunction with the various effects of interface between FeSe and $\mathrm{SrTi}{\mathrm{O}}_3$ substrate. By employing an electric-double-layer transistor configuration, which enables both the electrostatic carrier doping and electrochemical thickness tuning, we investigated the interfacial effect on the high-$T_{\mathrm{c}}$ phase at around 40 K in FeSe films deposited on $\mathrm{SrTi}{\mathrm{O}}_3$, MgO, and $\mathrm{KTa}{\mathrm{O}}_3$ substrates. The systematic study on thickness dependence of transport properties under a certain gate voltage reveals the universal trend of the onset $T_{\mathrm{c}}$ against the Hall coefficient in all the FeSe films, irrespective of the substrate materials in which the different contribution of interfacial effect is expected. The independence of the highest $T_{\mathrm{c}}$ on substrate materials evidences that the high-$T_{\mathrm{c}}$ superconductivity at around 40 K does not primarily originate from a specific interface combination but from a charge carrier filling at specific electronic band structure.

We consider the Dirac electron scattering off a pointlike impurity absorbed on the surface of a topological insulator, which is irradiated by a beam of circularly polarized light. It is found that the Dirac electron backscattering is allowed even for a nonmagnetic impurity due to the reshuffled spectrum caused by the light, and so exhibits interesting spin texture and Friedel oscillation in the real space. Furthermore, in the charge density of states, the interplay of the light irradiation and impurity scattering can lead to an in-gap bound state around the Dirac point, heavily modulating the Dirac dispersion. We discuss the different scenarios for resonant and off-resonant lights in detail. The impurity scattering feature is sensitive to the parameters of the polarized light, which suggests a possibility to optically manipulate the topological surface states.

We study the role of topological edge states of light in the transport of thermally generated radiation in a closed cavity at a thermodynamic equilibrium. It is shown that even in the zero temperature limit—when the field fluctuations are purely quantum mechanical—there is a persistent flow of electromagnetic momentum in the cavity in closed orbits, deeply rooted in the emergence of spatially separated unidirectional edge state channels. It is highlighted that the electromagnetic orbital angular momentum of the system is nontrivial, and that the energy circulation is towards the same direction as that determined by incomplete cyclotron orbits near the cavity walls. Our findings open inroads in topological photonics and suggest that topological states of light can determine novel paradigms in the context of radiative heat transport.

Double Weyl nodes are topologically protected band crossing points which carry chiral charge $\pm 2$. They are stabilized by $C_4$ point-group symmetry and are predicted to occur in ${\mathrm{SrSi}}_2$ or ${\mathrm{HgCr}}_2{\mathrm{Se}}_4$. We study their stability and physical properties in the presence of a disorder potential. We investigate the density of states and the quantum transport properties at the nodal point. We find that, in contrast to their counterparts with unit chiral charge, double Weyl nodes are unstable to any finite amount of disorder and give rise to a diffusive phase, in agreement with the predictions of Goswami and Nevidomskyy [Phys. Rev. B 92, 214504 (2015)] and Bera, Sau, and Roy [Phys. Rev. B 93, 201302 (2016)]. However, for finite system sizes a crossover between pseudodiffusive and diffusive quantum transport can be observed.

Semiconductor lasers are strongly altered by adding spin-polarized carriers. Such spin lasers could overcome many limitations of their conventional (spin-unpolarized) counterparts. While the vast majority of experiments in spin lasers employed zinc-blende semiconductors, the room-temperature electrical manipulation was first demonstrated in wurtzite GaN-based lasers. However, the underlying theoretical description of wurtzite spin lasers is still missing. To address this situation, focusing on (In,Ga)N-based wurtzite quantum wells, we develop a theoretical framework in which the calculated microscopic spin-dependent gain is combined with a simple rate equation model. A small spin-orbit coupling in these wurtzites supports simultaneous spin polarizations of electrons and holes, providing unexplored opportunities to control spin lasers. For example, the gain asymmetry, as one of the key figures of merit related to spin amplification, can change the sign by simply increasing the carrier density. The lasing threshold reduction has a nonmonotonic dependence on electron-spin polarization, even for a nonvanishing hole spin polarization.

Controlling the temperature in architectures involving nanoparticles and substrates is a key issue for applications involving micro- and nanoscale heat transfer. We study the thermal behavior of a single nanoparticle interacting with a flat substrate under external monochromatic illumination, and with thermal radiation as the unique heat loss channel. We develop a model to compute the temperature of the nanoparticle, based on an effective dipole-polarizability approach. Using numerical simulations, we thoroughly investigate the impacts of various parameters affecting the nanoparticle temperature, such as the nanoparticle-to-substrate gap distance, the incident light wavelength and polarization, or the material resonances. This study provides a tool for the thermal characterization and design of micro- or nanoscale systems coupling substrates with nanoparticles or optical antennas.

We investigate a spin-electricity conversion effect in a topological insulator/ferromagnet heterostructure. In the spin-momentum-locked surface state, an electric current generates nonequilibrium spin accumulation, which causes a spin-orbit torque that acts on the ferromagnet. When spins in the ferromagnet are completely parallel to the accumulated spin, this spin-orbit torque is zero. In the presence of spin excitations, however, a coupling between magnons and electrons enables us to obtain a nonvanishing torque. In this paper, we consider a model of the heterostructure in which a three-dimensional magnon gas is coupled with a two-dimensional massless Dirac electron system at the interface. We calculate the torque induced by an electric field, which can be interpreted as a magnon spin current, up to the lowest order of the electron-magnon interaction. We derive the expressions for high and low temperatures and estimate the order of magnitude of the induced spin current for realistic materials at room temperature.

We investigate the surface electronic structures of polar $1T^{\prime }\text{−}\mathrm{MoT}{\mathrm{e}}_2$, the Weyl semimetal candidate realized through the nonpolar-polar structural phase transition, by utilizing the laser angle-resolved photoemission spectroscopy combined with first-principles calculations. Two kinds of domains with different surface band dispersions are observed from a single-crystalline sample. The spin-resolved measurements further reveal that the spin polarizations of the surface and the bulk-derived states show the different domain dependences, indicating the opposite bulk polarity. For both domains, some segmentlike band features resembling the Fermi arcs are clearly observed. The patterns of the arcs present the marked contrast between the two domains, respectively agreeing well with the slab calculation of (0 0 1) and (0 0 −1) surfaces. The present result strongly suggests that the Fermi arc connects the identical pair of Weyl nodes on one side of the polar crystal surface, whereas it connects between the different pairs of Weyl nodes on the other side.

Defect tolerance can be critically important for optoelectronics. GaN, specifically, tolerates a relatively large concentration of threading dislocations, but the physical origin of this tolerance remains a mystery. First-principles calculations reveal the removal of deep-level states from edge dislocations by oxygen passivation. This removal is, however, not a thermodynamic ground state but kinetically driven. Oxygen incorporation during growth can be harmful; it becomes beneficial if introduced in the cooling-down phase or post-growth thermal treatment at a significantly lower temperature. Our findings extend first-principles defect study to the nonequilibrium regime where low-diffusion-barrier defects affect electronic behavior of semiconductors in unexpected fashion.

Robust random telegraph conductivity fluctuations have been observed in ${\mathrm{La}}_{0.86}{\mathrm{Ca}}_{0.14}{\mathrm{MnO}}_3$ manganite single crystals. At room temperatures, the spectra of conductivity fluctuations are featureless and follow a $1/f$ shape in the entire experimental frequency and bias range. Upon lowering the temperature, clear Lorentzian bias-dependent excess noise appears on the $1/f$ background and eventually dominates the spectral behavior. In the time domain, fully developed Lorentzian noise appears as pronounced two-level random telegraph noise with a thermally activated switching rate, which does not depend on bias current and applied magnetic field. The telegraph noise is very robust and persists in the exceptionally wide temperature range of more than 50 K. The amplitude of the telegraph noise decreases exponentially with increasing bias current in exactly the same manner as the sample resistance increases with the current, pointing out the dynamic current redistribution between percolation paths dominated by phase-separated clusters with different conductivity as a possible origin of two-level conductivity fluctuations.

Tuning competing ordering mechanisms with hydrostatic pressure in the $4d$ intermetallic compound ${\mathrm{Mo}}_3{\mathrm{Sb}}_7$ reveals an intricate interplay of structure, magnetism, and superconductivity. Synchrotron x-ray diffraction and magnetic susceptibility measurements, both employing diamond anvil cell technologies, link a first-order structural phase transition to a doubling of the superconducting transition temperature. In contrast to the spin-dimer picture for ${\mathrm{Mo}}_3{\mathrm{Sb}}_7$, we deduce from x-ray absorption near-edge structure and dc magnetization measurements at ambient pressure that ${\mathrm{Mo}}_3{\mathrm{Sb}}_7$ should possess only very small, itinerant magnetic moments. The pressure evolution of the superconducting transition temperature strongly suggests its enhancement is due to a difference in the phonon density-of-states with changed crystal symmetry.

We performed angle-resolved photoemission spectroscopy (ARPES) experiments on the surface states of ${\mathrm{SrTiO}}_3$(001) using linearly and circularly polarized light to investigate the subband structures of out-of-plane $d_{xz/yz}$ orbitals and chiral orbital angular momentum (OAM). The data taken in the first Brillouin zone reveal new subbands for $d_{xz/yz}$ orbitals with Fermi wave vectors of 0.25 and $0.45{\AA }^{-1}$ in addition to the previously reported ones. As a result, there are at least two subbands for all the Ti $3d t_{2g}$ orbitals. Our circular dichroism ARPES data are suggestive of a chiral OAM structure in the surface states and may provide clues to the origin of the linear Rashba-like surface band splitting.

We demonstrate theoretically that the interaction of electrons in gapped Dirac materials (gapped graphene and transition-metal dichalchogenide monolayers) with a strong off-resonant electromagnetic field (dressing field) substantially renormalizes the band gaps and the spin-orbit splitting. Moreover, the renormalized electronic parameters drastically depend on the field polarization. Namely, a linearly polarized dressing field always decreases the band gap (and, particularly, can turn the gap into zero), whereas a circularly polarized field breaks the equivalence of valleys in different points of the Brillouin zone and can both increase and decrease corresponding band gaps. As a consequence, the dressing field can serve as an effective tool to control spin and valley properties of the materials and be potentially exploited in optoelectronic applications.