Spectral diffusion on ultralong time scales in low temperature glasses

Abstract

A dynamical theory is constructed to describe spectral diffusion in glasses in the temperature range near 1 Kelvin on long time scales. The theory invokes interacting tunneling centers (TLS) which provide an excess contribution to the spectral hole width which qualitatively accounts for the deviation from standard logarithmic line broadening observed by Maier et al. [Phys. Rev. Lett. 76, 2085 (1996)]. Alternative explanation schemes of the nonlogarithmic line broadening, avoiding interacting TLS, are discussed. We devise experimental tests which could be used to access the validity of the proposed theories.