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DY: Fachverband Dynamik und Statistische Physik
DY 10: Posters I
DY 10.8: Poster
Montag, 14. März 2011, 17:00–19:00, P4
Coherent-Potential approximation for noncrystalline structures — •Stephan Köhler1 and Walter Schirmacher1,2 — 1Institut für Physik, Univ. Mainz — 2Physik-Department E13, TU München
The Coherent Potential Approximation (CPA) has been used extensively in the past decades to calculate properties of disordered solids [1], although its derivation assumes an underlying lattice structure of the material. We present a general method to derive the CPA equations for an amorphous solid using techniques from Quantum field theory. The approach is applied to electrons moving in a spatially fluctuating potential and to diffusion in a material with random diffusion coefficient. The later problem is mathematically equivalent to scalar vibrational excitations (scalar phonons) in a solid with fluctuating sound velocity. The DC-AC crossover in the diffusive dynamics is equivalent to the boson peak anomaly in the vibrational spectrum [2]. Since the CPA equations do not specify the underlying probability distribution of the fluctuations it is possible to study characteristic quantities of disordered solids for different distributions and compare them to results obtained from the Self Consistent Born Approximation [3], which is the low-disorder limit of the CPA. [1] R. J. Elliot et al., Rev. Mod. Phys. 46, 465, (1974); [2] W. Schirmacher, M. Wagener, Philos. Mag. B65, 607 (1992); [3] C. Schirmacher et al., phys. stat. sol. (c) 5, 862 (2008)