Thermally induced abrupt shrinking of a donor state in a ferromagnetic semiconductor

Abstract

We address the thermally induced abrupt shrinking of a large-radius donor in a ferromagnetic semiconductor. The sudden and severe localization is viewed as the synergistic effect of the driving forces for localization provided by the thermally induced spin disorder and the tendency for self-trapping. To show this effect, we calculate the free energy of a donor state in a ferromagnetic semiconductor. The donor electron interacts with the atomic spins via an intra-atomic exchange interaction and with the atomic displacements via a short-range electron-lattice interaction. Consistent with our focus on temperatures well below the Curie temperature, the spin deviations are treated within the spin-wave approximation.