NMR measurement of drift velocity and phase fluctuations of sliding charge density waves in Rb 0.3MoO 3

Abstract

To determine the velocity of the charge density wave, voltage noise and 87Rb NMR spectra at an electric field of about 15 E T were measured together with I–V characteristics on a Rb 0.3MoO 3 crystal between 40 and 60K. NMR spectra are reproduced by use of a velocity distribution determined by the noise spectrum, showing that all the electrons condensed below the Peierls gap participate to the Fröhlich mode. A detailed study of NMR sidebands as well as the oscillatory behaviour of the spin echo amplitude demonstrates that the winding rate of the phase ν d = ( 1 2 π) dφ( R)/ dt is equal to the noise frequency ν n and gives evidence for the coherence of the CDW sliding motion. This coherence, as well as the stochastic fluctuations of the phase are discussed in the light of spin-spin relaxation time measurements as a function of the applied electric field (E/E T in the range 3–20) between 40 and 90 K. Comparison of voltage noise and NMR spectra between 60 and 90 K indicates that at moderate E/E T ratios large phase fluctuations occur in parts of the crystal which do not contribute to jCDW.