Dresden 2009 – wissenschaftliches Programm
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DY: Fachverband Dynamik und Statistische Physik
DY 26: Poster II
DY 26.2: Poster
Donnerstag, 26. März 2009, 16:00–18:00, P1A
Akhiezer-like sound attenuation in glasses — •Walter Schirmacher1,2, Constantin Tomaras2, and Bernhard Schmid1 — 1Institut für Physik, Universität Mainz, Staudinger Weg 7, D-55099 Mainz, Germany — 2Physik Department E13, TU München, James-Franck-Straße 1, D-85747 Garching
We investigate a 3-dimensional continuum model for vibrational excitations in a disordered environment, based on the anharmonic generalisation of Lame’s elasticity theory. The disorder is introduced into the theory via a spatially correlated fluctuating shear modulus µ(r). It is shown by a mean-field treatment that the low-frequency Brillouin linewidth (sound attenuation coefficient) obeys a Rayleigh law Γ(ω)∝ω4 in the case of zero anharmonicity. Including the additional anharmonic terms, we obtain an Akhiezer-like law Γ(ω)∝ Tω2, which arises from a combination of disorder and anharmonicity. The same effect leads to the temperature dependent enhancement of the excess density of states g(ω)/gDebye(ω), observed in Neutron scattering experiments at frequencies below the Boson peak. The crossover from the Akhiezer to the Rayleigh regime is in agreement with light scattering experiments.