NQR Study of the Pinning and Depinning of the Incommensurate Modulation Wave in the Presence of Impurities

Abstract

High temperature-resolution NQR measurements in an ultra pure Rb₂ZnCl₄ crystal and a mixed [Rb_1-x(NH₄)_x]₂ZnCl₄ crystal with a controlled amount of impurities (x = 0.01) verify the existence of a temperature region where the characteristic incommensurate line splitting is averaged out. The results show that for the system with high purity the averaging of the incommensurate splitting is due to large thermal fluctuations. In contrast, for the mixed crystal the added impurities seem to play the predominant role.