Spin beats and dynamical magnetization in quantum structures

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Abstract
A femtosecond-resolved Faraday spectroscopy has been developed to directly monitor spin dynamics in magnetically tunable semiconductor quantum wells. Tunable terahertz quantum beating of the optical polarization is observed from coherent excitation of the spin states Zeeman split by a single ultrathin magnetic tunneling barrier. Subsequent spin-flip scattering of a photoinjected spin-polarized excitons deposits a magnetic ‘‘imprint’’ in the barrier which is orientation dependent and persists for orders of magnitude longer than the carrier lifetime.