Phase Slip, Relaxation, and Field Effects in Charge-Density-Wave Conductors

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9424572 Thorne Charge-density-wave (CDW) phase slip and CDW relaxation as well as a recently discovered CDW field-effect modulation of CDW conduction will be explored. Transport and x-ray scattering experiments have indicated that phase slip is driven by strains in the CDW, that it occurs via homogeneous thermal nucleation of dislocation loops, and that slips strongly modify the strain profile near current contacts. The spatial distribution of phase slip and strain between and beyond current contacts will be measured, and compared with models for CDW dislocation nucleation and motion. Spatially-resolved measurements of noise and Shapiro steps will determine the effect of phase slips on CDW dynamics. The coherence of the CDW response will be probed near the Peirels transition, where phase slips should become very easy and the effect of impurity strains on slip may become important. Measurements in semiconducting materials such as TaS3 will investigate the effect of quasiparticle density on phase slip, which may be dramatic at low densities and low temperatures. Detailed spatially resolved measurements of time dependent CDW relaxation will be performed, in an attempt to develop quantitative understanding of the underlying mechanisms. Experiments will be performed to investigate the modulation of CDW conductance using FET-like structure were the semiconductor is replaced by a CDW conductor. %%% Charge density wave (CDW) conductors are among the richest systems in condense matter physics, and serve as a paradigm for study of many fundamental issues occurring in a variety of systems such as superconductors, insulators, materials growth ...etc. CDWs can be represented as a sinusoidal modulation of the electronic charge density occurring in materials with specific properties. The electrons in a CDW respond collectively and with some degree of coherence to ex ternal excitations such as electric fields. This proposal investigates the phase slip process, which is the process by which the CDW electrons are converted into normal electrons, near the contacts, in order to carry electricity from the CDW sample into the remaining part of the circuit. A number of electrical transport experiments are designed to explore the phase slip mechanism and related relaxation mechanisms as well as a recently discovered field- effect modulation of the CDW conduction. ***