title: Numerical simulation of the forbidden Bragg reflection spectra observed in ZnO.
abstract: Thermal motion induced (TMI) scattering is a unique probe of changes in electronic states with atomic displacements in crystals. We show that it provides a novel approach to extract atomic correlation functions. Using numerical calculations, we are able to reproduce the temperature-dependent energy spectrum of the 115 'forbidden' Bragg reflection in ZnO. Our previous experimental studies showed that the intensity growth of such reflections over a wide range of temperatures is accompanied by a dramatic change in the resonant spectral lineshape. This is the result of the interplay between the temperature-independent (TI) and temperature-dependent TMI contributions. Here, we confirm that the TI part of the resonant structure factor can be associated with the dipole-quadrupole contribution to the structure factor and show that the temperature-dependent part arises from the zinc and oxygen vibrations, which provide additional temperature-dependent dipole-dipole tensor components to the structure factor. By fitting the experimental data at various temperatures we have determined the temperature dependences of autocorrelation <u(x)(2)(Zn)> and correlation <u(x)(O)u(x)(Zn)> functions.
authors.affiliation: Physical Department of Moscow State University, 119899 Moscow, Russia. ovtchin@gmail.com
authors.forename: E N
authors.initials: EN
authors.lastname: Ovchinnikova
authors.forename: V E
authors.initials: VE
authors.lastname: Dmitrienko
authors.forename: A P
authors.initials: AP
authors.lastname: Oreshko
authors.forename: G
authors.initials: G
authors.lastname: Beutier
authors.forename: S P
authors.initials: SP
authors.lastname: Collins