Equilibrium and non-equilibrium properties of the charge density wave condensate in quasi-one dimensional conductors

本项目旨在了解准一维导体中电荷密度波（CDW）凝聚态在平衡和非平衡条件下的性质。在微波至红外/可见光谱范围（2cm -1-30000 cm-1）的单晶反射率测量中，结合直流输运实验，研究其平衡特性。我们对低频（即微波到远红外）范围特别感兴趣，在那里可以观察到cdw凝结水的集体激发。系统地研究了样品质量和掺杂对集体cdw模式的影响。我们进一步感兴趣的是正常电子，即非凝聚电子对集体cdw模式的影响，如屏蔽和阻尼效应；这些效应将通过测量施加直流电场的反射率来探测。该项目的第二个主要问题是使用时间分辨技术研究凝聚态cdw的非平衡特性：通过光泵浦可以创建高度相干的凝聚态cdw。我们计划用时域太赫兹光谱在1 - 100 cm-1范围内表征这种诱导态。我们想进一步研究单电子对cdw振幅模式的影响，利用泵浦-探针技术：通过选择性时域拉曼散射可以相干激发该模式并研究其在直流电场作用下的衰减。

The proposed project aims at the understanding of the properties of the charge density wave (CDW) condensate in quasi-one dimensional conductors unter equilibrium and non-equilibrium conditions. The equilibrium properties will be studied by reflectivity measurements on single crystals from the microwave to the infrared/visible spectral range (2 cm -1-30000 cm-1), supplemented by dc-transport experiments. We are in particular interested in the low-frequency (i.e. microwave to far-infrared) range where the collective excitations of the CDW-condensate are observed. The influence of the sample quality and doping on the collective CDW-mode will be studied in a systematic way. We are furthermore interested in the effects of normal, i.e. uncondensed electrons on the collective CDW-mode, like screening and damping effects; these effects will be probed by measuring the reflectivity with a dc-electric field applied. The second main issue of the project is the study of the non-equlilibrium properties of the condensed CDW-state using time-resolved techniques: By optical pumping one can create a highly coherent condensed CDW-state. We plan to characterize this induced state by time-domain terahertz spectroscopy in the range 1 - 100 cm-1. We furthermor want to study the influence of single electrons on the amplitude mode of the CDW-using the pump-probe technique: By selective time-domain Raman-scattering one can coherently excite this mode and study its decay while a dc-electric field is applied.