ORIGIN OF THE T1.3 POWER-LAW OF PURE DEPHASING FOR IMPURITY ELECTRONIC-TRANSITIONS IN AMORPHOUS SOLIDS

The standard tunnel model together with the diagonal modulation theory of dephasing has previously been used to explain the above power law for impurity electronic transitions for T less than or similar to 10 K. Crude approximations made in averaging over the two-level system (TLS) parameters led to the widely held view that the exponent is 1 + mu where mu is the exponent of the TLS density of states, rho(E) = rho0E(mu). We show that this is incorrect and that the temperature dependence is determined by the average value of the TLS asymmetry parameter [DELTA]E, where E is the tunnel splitting.