Low-temperature anomalous specific heat without tunneling modes: a simulation for a-Si with voids

Abstract

Using empirical potential molecular dynamics we compute dynamical matrix eigenvalues and eigenvectors for a 4096 atom model of amorphous silicon and a set of models with voids of different size based on it. This information is then employed to study the localization properties of the low-energy vibrational states, calculate the specific heat C(T) and examine the low-temperature properties of our models usually attributed to the presence of tunneling states in amorphous silicon. The results of our calculations for C(T) and "excess specific heat bulge" in the C(T)/T^3 vs. T graph for voidless a-Si appear to be in good agreement with experiment; moreover our investigation shows that the presence of localized low-energy excitations in the vibrational spectrum of our models with voids strongly manifests itself as a sharp peak in C(T)/T^3 dependence at T < 3K. To our knowledge this is the first numerical simulation that provides adequate agreement with experiment for the very low-temperature properties of specific heat in disordered systems within the limits of harmonic approximation.

5 pages with 2 ps figures, submitted to PRB

References in corpus (3)

• Interatomic Potential for Silicon Defects and Disordered Phases
• Environment Dependent Interatomic Potential for Bulk Silicon
• Approximate ab initio calculation of vibrational properties of hydrogenated amorphous silicon with inner voids

Cited by in corpus (6)

• Large and realistic models of Amorphous Silicon
• Two-Level Systems in Evaporated Amorphous Silicon
• Vector vibrations and the Ioffe-Regel crossover in disordered lattices
• Sample dependence of the structural, vibrational, and electronic properties of a-Si:H: A density-functional-based tight-binding study
• Two-level systems and growth-induced metastability in hydrogenated amorphous silicon
• Computational generation of voids in $a$-Si and $a$-Si:H by cavitation at low density