Mapping from current densities to vector potentials in time-dependent current density functional theory

URL:http://link.aps.org/doi/10.1103/PhysRevB.70.201102 DOI:10.1103/PhysRevB.70.201102Under reasonable assumptions the time- dependent particle density nsrW , td and the current density jW srW , td of a many-particle system that evolves under the action of external scalar and vector potentials VsrW , td and AW srW , td and is initially in the quantum state ucs0dl can be reproduced in another many-particle system with a different two-particle interaction, subjected to external potentials V8srW , td and AW 8srW , td and starting from an initial state uc8s0dl, which yields the same density and current as ucs0dl. Here we show that given the initial state of this other many-particle system, the potentials V8srW , td and AW 8srW , td, if they exist, are uniquely determined up to gauge transformations that do not alter the initial state. As a special case, we obtain a simpler proof of the Runge-Gross theorem for time-dependent current density functional theory. This theorem provides a formal basis for the application of time- dependent current density functional theory to transport problems.The author acknowledges support from NSF Grant No. DMR-0313681

Current-Dependent Exchange-Correlation Potential for Dynamical Linear Response Theory

URL:http://link.aps.org/doi/10.1103/PhysRevLett.77.2037 DOI:10.1103/PhysRevLett.77.2037The frequency-dependent exchange-correlation potential, which appears in the usual Kohn- Sham formulation of a time-dependent linear response problem, is a strongly nonlocal functional of the density, so that a consistent local density approximation generally does not exist. This problem can be avoided by choosing the current density as the basic variable in a generalized Kohn-Sham theory. This theory admits a local approximation which, for fixed frequency, is exact in the limit of slowly varying densities and perturbing potentials.We acknowledge support from NSF Grants No. DMR- 9403908 and No. DMR-9308011

Collective modes and electronic spectral function in smooth edges of quantum hall systems

URL:http://link.aps.org/doi/10.1103/PhysRevB.54.R14309 DOI:10.1103/PhysRevB.54.R14309We present a microscopic theory of the collective modes of a ''smooth'' edge of a quantum Hall system, showing under what conditions these modes can be described as a set of independent bosons. We then calculate the electronic spectral function in an independent-boson model—a procedure that reduces to standard bosonization in the limit of ''sharp'' edge. The I-V tunneling characteristics deduced from this model exhibit, for low voltage, a power-law behavior, with exponents that differ significantly from those of the sharp edge model.We gratefully acknowledge support from NSF Grant No.DMR-9403908. One of us (S.C.) acknowledges travel support from Scuola Normale Superiore

Relaxation in Time-Dependent Current-Density-Functional Theory

URL:http://link.aps.org/doi/10.1103/PhysRevLett.96.016405 DOI:10.1103/PhysRevLett.96.016405We apply the time-dependent current-density-functional theory to the study of the relaxation of a closed many-electron system evolving from a nonequilibrium initial state. We show that the self-consistent unitary time evolution generated by the exchange-correlation vector potential irreversibly drives the system to equilibrium. We also show that the energy dissipated in the Kohn-Sham system, i.e., the noninteracting system whose particle and current densities coincide with those of the physical system under study, is related to the entropy production in the real system.We acknowledge financial support from NSF Grant No. DMR-0313681 and the kind hospitality of the Scuola Normale Superiore in Pisa, where part of this work was completed

Temperature dependence of persistent spin currents in a spin-orbit-coupled electron gas: A density-matrix approach

URL:http://link.aps.org/doi/10.1103/PhysRevB.77.155315 DOI:10.1103/PhysRevB.77.155315We present a simple analytical method, based on the canonical density matrix, for the calculation of the equilibrium spin current as a function of temperature in a two- dimensional electron gas with both Rashba and Dresselhaus spin-orbit coupling terms. We find that the persistent spin current is extremely robust against thermal disorder: its variation with temperature is exponentially small (∝e−TF∕T) at temperatures much smaller than the Fermi temperature TF and changes to a power law TF∕T for T⪢TF

Theory of spin Coulomb drag in spin-polarized transport

URL:http://link.aps.org/doi/10.1103/PhysRevB.62.4853 DOI:10.1103/PhysRevB.62.4853We introduce a distinctive feature of spin-polarized transport, the spin Coulomb drag: there is an intrinsic source of friction for spin currents due to the Coulomb interaction between spin “up” and spin “down” electrons. We calculate the associated “spin trans-resistivity” in a generalized random-phase approximation and show that, to the leading order in the interactions, it has no contribution from correlated impurity scattering. We show that, in an appropriate range of parameters, such resistivity is measurable, and we propose an experiment to measure it.This research was supported by NSF Grant No. DMR-9706788

Non- V -representability of currents in time-dependent many-particle systems

URL:http://link.aps.org/doi/10.1103/PhysRevB.71.245103 DOI:10.1103/PhysRevB.71.245103We argue that an arbitrarily chosen time-dependent current density is generically non-V-representable in a many-particle system; i.e., it cannot be obtained by applying only a time-dependent scalar potential to the system. Furthermore, we show by a concrete example that even a current that is V-representable in an interacting many-particle system may (and in general will) turn out to be non-V-representable when the interaction between the particles is turned off.The authors acknowledge support from NSF Grant No. DMR-0313681

Spin-Hall effect and spin-Coulomb drag in doped semiconductors

doi: 10.1088/0953-8984/21/25/253202In this review, we describe in detail two important spin-transport phenomena: the extrinsic spin-Hall effect (coming from spin-orbit interactions between electrons and impurities) and the spin-Coulomb drag. The interplay of these two phenomena is analyzed. In particular, we discuss the influence of scattering between electrons with opposite spins on the spin current and the spin accumulation produced by the spin-Hall effect. Future challenges and open questions are briefly discussed.This work was financially supported by NSF grant no. DMR-0705460 and DFG grant HA5893/1-1

Time-Dependent Density-Functional Theory beyond the Local-Density Approximation

URL:http://link.aps.org/doi/10.1103/PhysRevLett.97.036403 DOI:10.1103/PhysRevLett.97.036403Approximations for the ground-state exchange-correlation potential of density-functional theory have reached a high level of sophistication. By contrast, time- or frequency-dependent exchange-correlation potentials are still being treated in a local approximation. Here we propose a novel approximation scheme, which effectively brings the power of the generalized gradient approximation (GGA) and meta-GGA to time-dependent density-functional theory. The theory should allow a more accurate treatment of strongly inhomogeneous electronic systems (e.g. molecular junctions) while remaining essentially exact for slowly varying densities and slowly varying external potentials.This work was supported by DOE under Grant No. DE-FG02-05ER46203

Analytic expression for the diamagnetic susceptibility of a uniform electron gas

URL:http://link.aps.org/doi/10.1103/PhysRevB.74.193108 DOI:10.1103/PhysRevB.74.193108The diamagnetic (Landau) susceptibility is a key ingredient in current-density functional theory. We calculate this quantity of a uniform electron gas beyond the random-phase approximation and present an analytic expression for it which recovers the exact high-density limit.This work was supported by DOE under Grant No. DEFG02-05ER46203. We acknowledge very helpful discussions with John P. Perdew. Part of the computational work was done at Tulane University