Experimental Probes of Density Wave Deformations

本实验项目主要研究准一维导体中电荷密度波（CDW）和自旋密度波（SDW）的性质。在这些状态下，电子电荷和/或自旋密度是空间调制的，其波长与底层晶体的波长不同。然而，许多异常性质是由于密度波（DW）本身是可变形的，并且它的变形可以带电，可以相互作用，也可以与晶体中的其他电荷和缺陷相互作用。本项目重点研究这种变形在以下方面的影响：1)改变DW材料的弹性特性，2)允许电流注入DW，以及3)在低温下将材料驱动成玻璃状状态。实验技术包括：1)电调制红外传输（研究蓝青铜CDW中伴随极化和电流注入的带电变形）；2)交流量热法研究比热；3)低频弹性测量，使用射频腔与小磁铁一起对小样品进行应变。这些技术的结合使得在CDW材料中寻找玻璃化转变成为可能。这个研究项目本质上是跨学科的，涉及几名研究生，他们接受了优秀的培训，为在工业、政府实验室或学术界的职业生涯做准备。本实验研究项目致力于研究“准一维导电”材料的性质。这些材料包括三硒化钽和三氧化二钼钾，它们的晶体形式通常是针状的，并且只允许沿一个方向导电。在某些情况下，这些化合物在低温下经历转变到不寻常的状态，在这种状态下，电荷的运动以一种相关的方式发生，即电荷密度波（CDW）。一个相关的状态被称为自旋密度波（SDW）。准一维导体中的CDW和SDW状态具有空间调制的电子电荷和/或自旋密度，其波长与底层晶体的波长不同。CDW状态下的导电是随着整个波的移动而发生的，而不是像铜那样由单个电荷的移动而发生的。然而，许多异常性质是由于密度波（DW）本身是可变形的，并且它的变形可以带电，可以相互作用，也可以与晶体中的其他电荷和缺陷相互作用。本项目主要研究这种变形在以下方面的影响：1)改变DW材料的弹性特性；2)允许电流注入DW； 3)在低温下将材料驱动成玻璃状状态。实验技术包括：1)电调制红外传输（研究蓝青铜CDW中伴随极化和电流注入的带电变形）；2)交流量热法研究比热；3)低频弹性测量，使用射频腔与小磁铁一起对小样品进行应变。这些技术的结合使得在CDW材料中寻找玻璃化转变成为可能。这个研究项目本质上是跨学科的，涉及几名研究生，他们接受了优秀的培训，为在工业、政府实验室或学术界的职业生涯做准备。＊＊＊

w:\awards\awards96\*.doc 9731257 Brill This experimental research project is devoted to properties of Charge Density Waves (CDW) and Spin Density Waves (SDW) in quasi- one-dimensional conductors. In these states, the electronic charge and/or spin density is spatially modulated, with a wavelength which differs from that of the underlying crystal. Many of the anomalous properties, however, result from the fact the Density Wave (DW) itself is deformable, and that its deformations, which can be charged, interact with each other and with other charges and defects in the crystal. This project focuses on the effect of such deformations in 1) modifying the elastic properties of DW materials, 2) allowing current to be injected into the DW, and 3) driving materials into glass-like states at low temperatures. Experimental techniques include: 1) electromodulated infrared transmission (to study charged deformations that accompany polarization and current injection in the CDW in blue bronze); 2) ac calorimetry to study the specific heat; and, 3) low frequency elastic measurements, which are made using a radio frequency cavity in conjunction with small magnets to strain the small samples. The combination of these techniques allows a search for glass-transitions in CDW materials. This research program is interdisciplinary in nature and involves several graduate students, who receive excellent training in preparation for careers in industry, government laboratories or academia. %%% This experimental research project is devoted to properties of "quasi-one-dimensional conducting" materials. These materials, which include Tantalum Triselenide and Potassium Molybdenum Trioxide, are often needle-like in their crystal forms and allow for electrical conduction along only one direction. These compounds in some cases undergo transitions at low te mperature to unusal states in which the motion of electrical charge occurs in a correlated way, in Charge Density Waves (CDW). A related state is called a Spin Density Wave (SDW). Such CDW and SDW states in quasi-one-dimensional conductors feature electronic charge and/or spin density which is spatially modulated, with a wavelength which differs from that of the underlying crystal. Electrical conduction in the CDW state occurs as the whole wave moves, rather than by individual charge motion as in copper. Many of the anomalous properties, however, result from the fact the Density Wave (DW) itself is deformable, and that its deformations, which can be charged, interact with each other and with other charges and defects in the crystal. This project focuses on the effect of such deformations in 1) modifying the elastic properties od DW materials, 2) allowing electrical current to be injected in to the DW, and 3) driving materials into glass-like states at low temperatures. Experimental techniques include: 1) electromodulated infrared transmission (to study charged deformations that accompany polarization and current injection in the CDW in blue bronze); 2) ac calorimetry to study the specific heat; and, 3) low frequency elastic measurements, which are made using a radio frequency cavity in conjunction with small magnets to strain the small samples. The combination of these techniques allows a search for glass-transitions in CDW materials. This research program is interdisciplinary in nature and involves several graduate students, who receive excellent training in preparation for careers in industry, government laboratories or academia. ***