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The broken inversion symmetry at the surface of a metallic film (or, more generally, at the interface between a metallic film and a different metallic or insulating material) greatly amplifies the influence of the spin-orbit interaction on the surface properties. The best known manifestation of this effect is the momentum-dependent splitting of the surface-state energies (Rashba effect). Here we show that the same interaction also generates a spin polarization of the bulk states when an electric current is driven through the bulk of the film. For a semi-infinite jellium model, which is representative of metals with a closed Fermi surface, we prove as a theorem that regardless of the shape of the confinement potential, the induced surface spin density at each surface is given by S = -γhz × j, where j is the particle current density in the bulk, z the unit vector normal to the surface, and γ = h/4mc2 contains only fundamental constants. For a general metallic solid, γ becomes a material-specific parameter that controls the strength of the interfacial spin-orbit coupling. Our theorem, combined with an ab initio calculation of the spin polarization of the current-carrying film, enables a determination of γ, which should be useful in modeling the spin-dependent scattering of quasiparticles at the interface. [ABSTRACT FROM AUTHOR]

We present a rigorous formulation of the time-dependent density-functional theory for interacting lattice electrons strongly coupled to cavity photons. We start with an example of one particle on a Hubbard dimer coupled to a single photonic mode, which is equivalent to the single mode spin-boson model or the quantum Rabi model. For this system we prove that the electron-photon wave function is a unique functional of the electronic density and the expectation value of the photonic coordinate, provided the initial state and the density satisfy a set of well defined conditions. Then we generalize the formalism to many interacting electrons on a lattice coupled to multiple photonic modes and prove the general mapping theorem. We also show that for a system evolving from the ground state of a lattice Hamiltonian any density with a continuous second time derivative is locally v representable. [ABSTRACT FROM AUTHOR]

We investigate the proximity effect in diffusive superconducting hybrid structures with a spin-orbit (SO) coupling. Our study is focused on the singlet-triplet conversion and the generation of long-range superconducting correlations in ferromagnetic elements. We derive the quasiclassical equations for the Green's functions including the SO coupling terms in form of a background SU(2) field. With the help of these equations, we first present an interesting complete analogy between the spin diffusion process in normal metals and the generation of the triplet components of the condensate in a diffusive superconducting structure in the presence of SO coupling. From this analogy it turns out naturally that the SO coupling is an additional source of the long-range triplet component (LRTC) besides the magnetic inhomogeneities studied in the past. This analogy opens a range of possibilities for the generation and manipulation of the triplet condensate in hybrid structures. In particular we demonstrate that a normal metal with SO coupling can be used as source of LRTC if attached to a superconductor-ferromagnet bilayer. We also demonstrate an explicit connection between an inhomogeneous exchange field and SO coupling mechanisms for the generation of the LRTC and establish the conditions for the appearance of the LRTC in different geometries. Our work gives a global description of the singlet-triplet conversion in hybrid structures in terms of generic spin fields and our results are particularly important for the understanding of the physics underlying spintronic devices with superconductors. [ABSTRACT FROM AUTHOR]

Time-dependent density functional theory (TDDFT) for quantum many-body systems on a lattice is formulated rigorously. We prove the uniqueness of the density-to-potential mapping and demonstrate that a given density is v representable if the initial many-body state and the density satisfy certain well-defined conditions. In particular, we show that for a system evolving from its ground state any density with a continuous second time derivative is locally in time v representable and therefore the lattice TDDFT is guaranteed to exist. The TDDFT existence and uniqueness theorem is valid for any connected lattice, independently of its size, geometry, and/or spatial dimensionality. General statements of the existence theorem are illustrated on a pedagogical exactly solvable example, which displays all the details and subtleties of the proof in a transparent form. In conclusion we briefly discuss remaining open problems and directions for future research. [ABSTRACT FROM AUTHOR]

A rigorous formulation of time-dependent current density functional theory (TDCDFT) on a lattice is presented. The density-to-potential mapping and the V-representability problems are reduced to a solution of a certain nonlinear lattice Schrödinger equation, to which the standard existence and uniqueness results for nonlinear differential equations are applicable. For two versions of the lattice TDCDFT, we prove that any continuous-in-time current density is locally V-representable (both interacting and noninteracting), provided that in the initial state the local kinetic energy is nonzero everywhere. In most cases of physical interest, the V-representability should also hold globally in time. These results put the application of TDCDFT to any lattice model on a firm foundation, and pave the way for studying exact properties of exchange-correlation potentials. [ABSTRACT FROM AUTHOR]

We extend a recent formulation of quantum continuum mechanics [J. Tao et al., Phys. Rev. Lett. 103, 086401 (2009)] to many-body systems subjected to a magnetic field. To accomplish this, we propose a modified Lagrangian approach, in which the motion of infinitesimal volume elements of the system is referred to the "quantum convective motion" that the magnetic field produces already in the ground state of the system. In the linear approximation, this approach results in a redefinition of the elastic displacement field u, such that the particle current j contains both an electric displacement and a magnetization contribution: j = j0 + n0∂tu + ∇ × (j0 × u), where n0 and j0 are the particle density and the current density of the ground state and ∂t is the partial derivative with respect to time. In terms of this displacement, we formulate an "elastic approximation" analogous to the one proposed in the absence of magnetic field. The resulting equation of motion for u is expressed in terms of ground-state properties, the one-particle density matrix and the two-particle pair-correlation function, and in this form it neatly generalizes the equation obtained for vanishing magnetic field. [ABSTRACT FROM AUTHOR]

Through the exact solution of a two-electron singlet system interacting with a monochromatic laser we prove that all adiabatic density functionals within time-dependent density-functional theory are not able to discern between resonant and nonresonant (detuned) Rabi oscillations. This is rationalized in terms of a fictitious dynamical exchange-correlation (xc) detuning of the resonance while the laser is acting. The nonlinear dynamics of the Kohn-Sham system shows the characteristic features of detuned Rabi oscillations even if the exact resonant frequency is used. We identify the source of this error in a contribution from the xc functional to the set of nonlinear equations that describes the electron dynamics in an effective two-level system. The constraint of preventing the detuning introduces a new strong condition to be satisfied by approximate xc functionals. [ABSTRACT FROM AUTHOR]

We present an analytical study of the Dyakonov-Perel spin relaxation time for degenerate electrons in a photoexcited electron-hole liquid in intrinsic semiconductors exhibiting a spin-split band structure. The Dyakonov-Perel spin relaxation of electrons in these materials is controlled by electron-hole scattering, with small corrections from electron-electron scattering and virtually none from electron-impurity scattering. We derive simple expressions (one-dimensional and two-dimensional integrals respectively) for the effective electron-hole and electron-electron scattering rates which enter the spin relaxation time calculation. The electron-hole scattering rate is found to be comparable to the scattering rates from impurities in the electron liquid—a common model for n-type doped semiconductors. As the density of electron-hole pairs decreases (within the degenerate regime), a strong enhancement of the scattering rates and a corresponding slowing down of spin relaxation is predicted due to exchange and correlation effects in the electron-hole liquid. In the opposite limit of high density, the original Dyakonov-Perel model fails due to decreasing scattering rates and is eventually superseded by free precession of individual quasiparticle spins. [ABSTRACT FROM AUTHOR]