CHARGE-DENSITY-WAVE PHASE-SLIP AND CONTACT EFFECTS IN MBSE(3)

We describe a detailed experimental study of phase slip in the charge-density-wave (CDW) conductor NbSe3. Phase slip is required for conversion between CDW current and single-particle current near current contacts. For both CDW's in NbSe3, the CDW current I-c, proportional to the phase-slip rate, exhibits a diodelike dependence upon an excess voltage V-ps, the phase-slip voltage. For a given I-c (slip rate), V-ps increases strongly with decreasing temperature, and at corresponding temperatures is roughly an order of magnitude larger for the T-p1 CDW than for the T-p2 CDW. Current contacts applied to the side of the crystal may lead to inhomogeneous current injection and allow CDW deformations and slip to extend beyond the contacts. Voltage contacts shunt current out of the crystal, and may cause CDW deformations and slip in their vicinity. We describe improved measurements of phase slip using nonperturbing voltage contacts and end current contacts formed by selected-area ion implantation. The results are consistent with those obtained using side contacts, confirm the interpretation of V-ps as the driving force behind phase slip, and provide information about the distribution of slip near the current contacts. The predictions of Ramakrishna et al. for phase slip by thermally activated of edge dislocation loops nucleation account for some qualitative features of our experiments but are in serious quantitative disagreement, suggesting that other slip mechanisms may be important.