Speaker
Dr
Guillaume Beutier
(CNRS)
Description
Reflections forbidden by crystallographic rules can be observed when the energy of incident x-rays is tuned to an absorption edge of the material. When the site symmetry of the resonant atoms is such that dipole-dipole resonant scattering is also forbidden, one can still measure intensity at the position of the forbidden reflection: it is related to the transcient atomic displacements of the resonant atoms from their high-symmetry sites, due to thermal motion [1]. These so-called Thermal Motion Induced (TMI) resonant reflections have been measured in Germanium and Wurtzites crystals ZnO, GaN and CdSe [2,4]. The intensity can be reproduced with a single low energy optical phonon mode.
This experimental method can be used to measure atomic displacements correlations [3] and has potential applications to study systems with interesting electron-lattice coupling effects. It would benefit from the possibility to excite selectively a single optical phonon mode.
References:
[1] Dmitrienko V E and Ovchinnikova E N, Acta Cryst. A56, 340-347 (2000).
[2] Collins S P, Laundy D, Dmitrienko V E, Mannix D and Thompson P, Phys. Rev. B 68, 064110 (2003).
[3] Ovchinnikova E N, Dmitrienko V E, Oreshko A P, Beutier G and Collins S P, J. Phys.: Condens. Matter 22, 355404 (2010).
[4] Beutier G, Collins S P, Nisbet G, Ovchinnikova E N, Dmitrienko V E, Eur. Phys. J. Special Topics 208, 53-67 (2012).
Primary author
Dr
Guillaume Beutier
(CNRS)
Co-authors
Prof.
Elena Ovchinnikova
(Moscow State University)
Dr
Gareth Nisbet
(Diamond Light Source)
Prof.
Steve Collins
(Diamond Light Source)
Prof.
Vladimir Dmitrienko
(Shubnikov Institute of Crystallography)
