Y. Kerachian

Pure spin current gratings in semiconductors generated by quantum interference

We demonstrate that the quantum mechanical interference between the probability amplitudes for the two-photon absorption of a fundamental (1.55 μm)∼150 fs pulse and for the one-photon absorption of a noncollinearly propagating second-harmonic (775 nm) pulse can create transient, ballistic, purely spin-polarized current gratings in bulk GaAs at room temperature. For fundamental and second-harmonic pulses having orthogonal linear polarizations, two periodically modulated ballistic spin-polarized current gratings are injected that have opposite spins and opposite propagation directions at each point along the grating. Consequently, there is no initial modulation of the charge current, carrier population, or net spin. Before the carrier momentum relaxes, the transport associated with these spin currents forms two oppositely spin-polarized population gratings that are exactly out of phase spatially and that decay by electronic spin diffusion in a time of 3.2 ps. In addition, charge density gratings are directl...

Quantum interference injection and control of spin-polarized transient current gratings in GaAs

Transient grating and quantum interference techniques are combined to inject and control spin-polarized currents (with or without an accompanying electrical current) in bulk GaAs at room temperature.

Femtosecond dynamics of ballistic charge current gratings in GaAs

We investigate the dynamics of ballistic charge currents, optically-injected into GaAs by quantum interference of 1550 and 775 nm, 150 fs pulses. Space-charge induced transport and ambipolar diffusion successively define the relaxation dynamics on a 500 fs-20 ps timescale.

Spin relaxation measurements in GaAs high above the band gap

When energy of the probe pulse is well above the band gap, we demonstrate that the correct spin relaxation time in bulk GaAs can be inferred only after carrier cooling, band dispersion and carrier statistics are taken into account

Spins...free of charge

Quantum interference of single and two photon absorption pathways connecting valence and conduction band states in a semiconductor allow one to generate spin currents with or without charge currents. The underlying principles for these generation processes are outlines. We offer experimental demonstration of pure spin currents in GaAs using two color beams configured collinearly to produce spatially homogeneous currents, or non-collinearly to produce spin current gratings.