Nonanalytic polarization response of a dipolar glass.

The polarization response of the dipolar glass KTa sub (1-x) Nb sub x O sub 3 (x=0.009) as a function of temperature (1. 815 K) and frequency (1 to 10 sup 4 Hz) is found to be a nonanalytic function of field, revealing the inadequacy of the usual nonlinear susceptibility description, as well as the incorrectness of even the linear response previously reported in such systems. A model based upon activated switching of two-level systems with a barrier distribution extending to zero energy adequately describes our data. Nonanalytic response and the associated phenomenon of reptation may be general features of dipolar glasses, as well as other random systems, including magnetic spin glasses.