Dresden 2003 – wissenschaftliches Programm

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DF: Dielektrische Festkörper

DF 4: Gl
äser Ib (gemeinsam FV DF/DY)

DF 4.10: Vortrag

Dienstag, 25. März 2003, 12:30–12:45, HSZ/403

Universality of Anomalous Excitations in Amorphous Solids — •Michael Schulz — Abteilung Theoretische Physik, Uni Ulm, 89069 Ulm, Germany

Acoustic and dielectric properties of glasses were intensively investigated during the last decades. An important result of these investigations was the discovery of universal low-temperature properties that are only weakly dependent an the structure of the amorphous solid. Such properties can be observed in the low temperature behavior of the specific heat, the thermal conductivity, the propagation of ultrasound, dielectric loss and some other properties governed by low-frequency modes.

A general proof for the universal existence of anomalous, non-Debye,vibrational excitations in amorphous is proposed. Starting from an ideal amorphous solid with fixed mean positions of all atoms and harmonic interactions, it was demonstrated that any increase of disorder leads stringently to an increase of the spectral density for low (and also veryhigh) frequencies. That means, the density of states shows additional contributions to the low frequency part of the standard Debye density, even the wave length of corresponding phonon like excitations is of an order of magnitude on which the amorphous solid is still homogeneous and the sound waves are not strongly effected by the disorder.