SPIN BEATS AND DYNAMICAL MAGNETIZATION IN QUANTUM STRUCTURES

A femtosecond-resolved Faraday spectroscopy has been developed to dire ctly monitor spin dynamics in magnetically tunable semiconductor quant um wells. Tunable terahertz quantum beating of the optical polarizatio n is observed from coherent excitation of the spin states Zeeman split by a single ultrathin magnetic tunneling barrier. Subsequent spin-fli p scattering of photoinjected spin-polarized excitons deposits a magne tic ''imprint'' in the barrier which is orientation dependent and pers ists for orders of magnitude longer than the carrier lifetime.