Hamburg 2001 – scientific programme

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HL: Halbleiterphysik

HL 8: Hauptvortrag

HL 8.1: Invited Talk

Monday, March 26, 2001, 14:30–15:15, S2

Inelastic X-ray scattering: new possibilities for Raman spectroscopy — •Tobias Ruf — Max-Planck-Institut fuer Festkoerperforschung, Heisenbergstr.1, 70569 Stuttgart

Inelastic X-ray scattering with meV resolution offers unique possibilities for studies of elementary excitations in solids. Dedicated beamlines at high-brilliance third-generation synchrotrons have recently become accessible for general users. Contrary to Raman spectroscopy with visible laser excitation, which in first order is limited to excitations at the Brillouin zone center, the wave vectors in hard X-ray Raman scattering are very large, and the crystal-momentum transfer in an inelastic scattering experiment can be continuously tuned across the whole Brillouin zone. In analogy to inelastic neutron scattering, this allows one to measure the dispersion of elementary excitations. However, the high collimation and beam quality of the X-rays makes it possible to investigate very small samples. This is very important for studies of new materials, where single crystals are usually rather tiny.

As an example for dispersion measurements of elementary excitations, we have obtained data for phonons in wurtzite GaN [1]. We have even observed dispersion effects of the phonon self energy, i.e., wave-vector-dependent changes in phonon frequencies and linewidths caused by isotope scattering, in isotopically mixed diamond [2]. The technique is rapidly gaining popularity also for studies of electronic excitations, for example in copper germanate.

[1] T. Ruf, J. Serrano, M. Cardona, P. Pavone, M. Pabst, M. Krisch, M. D’Astuto, T. Suski, I. Grzegory, and M. Leszczynski, Phys. Rev. Lett., in print (2001).

[2] T. Ruf, J. Serrano, M. Cardona, P. Pavone, M. Pabst, M. Krisch, M. D’Astuto, T. Suski, I. Grzegory, M. Leszczynski, and T. R. Anthony, in Proc. of the 25th ICPS (Osaka, 2000), (Springer-Verlag, Heidelberg, 2001), to be published.