Optical, electrical and magnetic manipulation of spins in semiconductors

Abstract

A variety of techniques are employed to investigate spin-dependent effects in semiconductors and quantum structures. Time-resolved Faraday rotation enables optical measurement and control of coherent electron- and nuclear-spin dynamics in these systems. Femtosecond pulses create a superposition of electron-spin states defined by a transverse magnetic field, and used to follow the phase, amplitude and location of spin precession in bulk materials and across dissimilar interfaces. Ultrafast pulses are also used to operate on coherent spin states by exploiting the ac Stark effect. Electrical gating of spin-engineered nanostructures provides continuous tunability and quenching of electron precession. Through the hyperfine interaction, nuclear spins may be strongly coupled to electrons polarized by photons or overlying ferromagnetic materials. Both electron- and hole-spin injections from ferromagnetic semiconductors into nearby quantum wells are demonstrated with spin-LED structures and electroluminescence polarization spectroscopy. Anisotropic spin injection efficiency is observed for holes polarized along or orthogonal to the current flow, while electrons show isotropic efficiency, demonstrating the importance of device geometry for spin injection and detection.