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

9424572索恩电荷密度波(CDW)相移和CDW弛豫，以及最近发现的CDW电导的CDW场效应调制。输运和X射线散射实验表明，相滑移是由CDW中的应变驱动的，它是通过位错环的均匀热形核发生的，并且滑移强烈地改变了电流接触附近的应变分布。测量了电流接触前后相滑移和应变的空间分布，并与CDW位错形核和运动模型进行了比较。噪声和夏皮罗步数的空间分辨测量将确定相位滑移对CDW动力学的影响。我们将在Peirels相变附近探讨CDW响应的相干性，在那里相滑移将变得非常容易，而杂质应变对滑移的影响可能变得重要。在半导体材料如TaS3中的测量将研究准粒子密度对相移的影响，这在低密度和低温下可能是戏剧性的。将对依赖于时间的CDW弛豫进行详细的空间分辨测量，试图发展对潜在机制的定量理解。在半导体被CDW导体取代的情况下，将进行实验来研究使用类FET结构的CDW电导的调制。电荷密度波(CDW)导体是凝聚态物理中最丰富的体系之一，是研究超导体、绝缘体、材料生长等各种体系中许多基本问题的范例。CDW可以表示为发生在具有特定性质的材料中的电子电荷密度的正弦调制。CDW中的电子对外界激励(如电场)具有一定程度的一致响应。该方案研究了相移过程，即CDW电子在触点附近转换为正常电子的过程，以便将电流从CDW样品输送到电路的其余部分。设计了大量的电输运实验，以探索相移机制和相关的驰豫机制，以及最近发现的CDW电导的场效应调制。***

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. ***