Light induced magnetization in semiconductors

Abstract

The absorption of circularly polarized light leads to a partial spin orientation (with respect to the propagation direction of radiation) of excited carriers in a direct gap semiconductor. Even for diamagnetic or diluted paramagnetic crystals, this optically induced spin-polarization is associated with a macroscopic magnetization due to the oriented magnetic spin moments. Since this effect is rather small, the light induced mangetization is determined by a novel combination of the method of optical pumping with a superconducting quantum interference detection. Several narrow gap semiconductors (InSb, Hg1−xCdxTe, Hg1−xMnxTe) were investigated, and the decisive role of band-structure details for the distribution of the initially oriented spins is discussed in detail. For the semimagnetic semiconductors, the effect of exchange interaction between the mobile carriers and the localized 3d-electrons of Mn2+-ions is considered. In addition the relative importance of the various spin-relaxation channels is treated within the framework of relaxation time models. The basic differences between this effect and other photomagnetization effects is stressed.