Ultrafast spin-polarized electrical currents injected in a strained zinc blende semiconductor by single color pulses

Abstract

Ultrafast ballistic electrical currents are generated through interband excitation of strained InGaAs∕GaAs quantum well samples at 295 K by 810 nm, 60 fs circularly polarized optical pulses. These currents are generated through quantum interference of optical absorption pathways associated with the orthogonally polarized components of the light field, and although the spin of the currents is not directly measured, they should also be spin polarized. The femtosecond transient currents are detected via the emitted tetrahertz (THz) radiation which has a bandwidth of ∼8THz. The THz amplitude scales linearly with injected carrier density up to ∼1018cm−3 beyond which state filling and carrier–carrier scattering cause a sublinear dependence. A peak current density of 9kA∕cm2 is obtained for a peak pump intensity of 250MW∕cm2.