Low-temperature properties of the orientational glassKBr1−x(CN)x

Abstract

The orientational glass $\mathrm{K}{\mathrm{Br}}_{1-x}{\left(\mathrm{CN}\right)}_x$ has been studied at temperatures between 0.05 and 5 K and for $0.01\le x\le 0.50$. The properties measured were specific heat, thermal expansion, thermal conductivity, and dielectric constant. With increasing $x$, the low-energy excitations associated with the orientational tunneling of interacting CN molecules closely approach in behavior the two-level states found in amorphous solids. As $x$ increases from 0.10 to 0.50, the density of excitations decreases by a factor of 100 while the phonon mean free path remains constant for $T<\mathrm{}0.5\mathrm{}$ K.