Temperature-induced distortions of electronic states observed via forbidden Bragg reflections in germanium - art. no. 073203

According to the adiabatic approximation, the electronic states of atoms in solids are bound up with thermal atomic motion. As a result, thermal-motio n-induced (TMI) anisotropy of x-ray susceptibility can appear for atoms occ upying positions with high symmetry. We report evidence for this effect fou nd in the very strong temperature dependence of the 006 forbidden Bragg ref lections from a germanium single crystal. The intensity of these reflection s increases or decreases drastically as the temperature rises from 30 K to 300 K, in contrast with nonforbidden reflections. It is found that the TMI anisotropy of the structure amplitude scales with the temperature as the me an square of the atomic displacements. This observation is very important f or understanding the intricate interplay between phonon and electronic prop erties of solids.