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Charge Current (charge + current)

Distribution by Scientific Domains
Physics and Astronomy100%

Selected Abstracts

Branching-induced spin polarization amplification in nonmagnetic semiconductors

PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 12 2006
S.-W. Jung
Abstract We study the spin injection in ferromagnet-tunnel barrier-semiconductor heterojunction structure embedded in the current-branching scheme. The current branching enables one to separately control the charge current from the spin current. As a result, it is possible to electrically control the spin current polarization within the semiconductor. Moreover, it can be enhanced further and may reach 100% by properly tuning the branched currents. Since the proposed scheme does not require low temperature operation, it may be a useful tool to generate the high spin current polarization at room temperature. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Optically driven Mott-Hubbard systems out of thermodynamic equilibrium

ANNALEN DER PHYSIK, Issue 12 2009
A. Lubatsch
Abstract We consider the Hubbard model at half filling, driven by an external, stationary laser field. This stationary, but periodic in time, electromagnetic field couples to the charge current, i.e. it induces an extra contribution to the hopping amplitude in the Hubbard Hamiltonian (photo-induced hopping). We generalize the dynamical mean-field theory (DMFT) for nonequilibrium with periodic-in-time external fields, using a Floquet mode representation and the Keldysh formalism. We calculate the non-equilibrium electron distribution function, the density of states and the optical DC conductivity in the presence of the external laser field for laser frequencies above and below the Mott-Hubbard gap. The results demonstrate that the system exhibits an insulator-metal transition as the frequency of the external field is increased and exceeds the Mott-Hubbard gap. This corresponds to photo-induced excitations into the upper Hubbard band. [source]

Photoinduced nonequilibrium spin, charge polarizations and spin-dependent current in quantum rings

PHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 3 2010
Z. G. Zhu
Abstract We investigate the spin-dependent dynamical response of a semiconductor quantum ring with a spin orbit interaction upon the application of a single and two linearly polarized, picosecond, asymmetric electromagnetic pulses in the presence of a static magnetic flux. We find that the pulse-generated electric dipole moment is spin dependent. It is also shown that the spin orbit interaction induces an extra SU(2) effective flux in addition to the static external magnetic flux which is reflected in an additional periodicity of the spin-dependent dipole moment. Furthermore, the pulses may induce a net dynamical charge currents and dynamical spin currents when the clockwise and anti-clockwise symmetry of the carrier is broken upon the pulse application. [source]

Coherence control of electron spin currents in semiconductors

PHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 10 2006
Henry M. van Driel
Abstract We provide an overview of some of our recent work on the use of one color and two color optical techniques to generate and control electronic spin currents in semiconductors for which a spin,orbit interaction exists. The generation process relies on the quantum interference between different absorption pathways, such as that between single and two photon absorption or those involving different polarization states of a monochromatic beam. For different crystal orientations and/or beam polarizations it is possible to generate a spin current with or without an electric current, and an electrical current with or without a spin current. In our experiments, which are conducted either at 80 K or 295 K, we typically employ nominally 100 fs pulses centered near 1500 and 750 nm. The currents generated are quasi-ballistic and the carriers typically move distances of ,1,10 nm, determined by the momentum relaxation time, which is of the order of 100 fs. The transient characteristics of spin-polarized electrical currents generated in strained GaAs at room temperature by ,100 fs pulses is detected by the emitted THz radiation. Pure spin currents can be detected by taking advantage of the accumulation of up and down spins on opposite sides of tightly focused pump beams. The spin states are detected through differential transmission measurements of tightly focused right and left circularly polarized, near-band-edge probe pulses, delayed by several picoseconds from the pump pulses to allow carrier thermalization to occur. By spatial scanning across the differential spin profiles and determining the amplitude of the response we are able to translate this into nm spatial resolution of spin displacement. Finally, the ability to generate ballistic currents using purely optical techniques allows us to generate transverse Hall-like currents, with transverse charge currents generated from pure spin currents and transverse spin currents generated from pure charge currents. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]