U.S.-France Cooperative Research: Charge-Density-Wave Materials and Dynamics

该奖项将支持美国和法国在凝聚态物理方面的合作研究项目。美国调查人员是：康奈尔大学的罗伯特·索恩博士、肯塔基大学的约瑟夫·布里尔博士、克莱姆森大学的格布雷·特塞马博士和海军研究实验室的T·M·特里特博士。法国同行是：格勒诺布尔甚低温研究中心的Pierre Monceau博士，以及南特和雷恩固态化学实验室的J.Rouxel博士和M.Sargent博士。电荷密度波(CDW)导体是凝聚态物理中最丰富的体系之一，它表现出与超导电性相似的集体电荷输运，以及与无序和许多自由度相关的显著的动力学效应。该项目的目标是1)制备新的和改进的材料，2)了解与CDW钉扎相关的弹性异常，以及3)了解双金属硒中应力诱导的密度波转变。该项目将分为以下三个部分：1)糟糕的材料质量一直是了解CDW系统进展的主要障碍。雷恩和南特的研究小组在制备新型无机低维导体方面拥有丰富的专业知识，而康奈尔大学的研究小组一直在开发方法来制备研究最广泛的CDW导体的更高纯度的晶体。建议在这些实验室之间进行合作，以制备具有更高纯度和形貌的晶体，并识别和探索其他有希望的材料系统。2)人们对CDW导体高度反常的机电性能知之甚少。肯塔基和格勒诺布尔小组建议在强磁场中进行高灵敏度的弹性模量值测量和超声波测量，以考察CDW振幅、正常载流子屏蔽和CDW-声子相互作用在这些性质中的作用。3)最近，Clemson、Rennes和Grioble群在准一维导体Ta-Mo-Se中发现了一种新的应力诱导金属半导体相变和非欧姆导电。与海军研究实验室合作，建议对应力晶体中的X射线和磁输运进行研究，以确定低温密度波态的性质。

This award will support a US-French collaborative research project in condensed matter physics. The US investigators are: Dr. Robert Thorne, Cornell University, Dr. Joseph Brill, University of Kentucky, Dr. Guebre Tessema, Clemson University, and Dr. T. M. Tritt, Naval Research Laboratory. The French counterparts are: Dr. Pierre Monceau, Center for Research on Very Low Temperatures, Grenoble, and Drs. J. Rouxel and M. Sargent from the Laboratories of Solid State Chemistry in Nantes and Rennes. Charge density wave (CDW) conductors are among the richest systems in condensed matter physics, exhibiting collective charge transport with many analogies to superconductivity and remarkable dynamical effects associated with disorder and many degrees of freedom. The goals of this project are 1) to prepare new and improved materials, 2) to understand the elastic anomalies associated with CDW pinning, and 3) to understand the stress-induced density wave transition in bi- metallic selenides. The project will be divided into three parts as follows: 1) Poor material quality has been a major obstacle to progress in understanding CDW systems. The research groups at Rennes and Nantes have great expertise in preparing novel inorganic low-dimensional conductors, while the Cornell group has been developing methods for preparing higher purity crystals of the most widely studied CDW conductors. A collaboration between these laboratories is proposed to prepare crystals with improved purity and morphology, and to identify and explore other promising materials systems. 2) The highly anomalous electromechanical properties of CDW conductors are poorly understood. High- sensitivity elastic modulus measurements in high magnetic fields and ultrasound measurements are proposed by the Kentucky and Grenoble groups to examine the role of the CDW amplitude, normal carrier screening and CDW-phonon interactions in these properties. 3) A novel stress-induced metal semi-conductor phase transition and non-ohmic conduction have recently been discovered by the Clemson, Rennes and Grenoble groups in the quasi-one-dimensional conductor tantalum-molybdenum selenide. In collaboration with the Naval Research Laboratory, X-ray and magnetotransport studies in stressed crystals are proposed to establish the nature of the low-temperature density wave state.