Electro-Optic Studies of Charge Density Wave Conductors

电荷密度波（CDW）材料，其中的CDW可以与一个小的电场脱钉作为模型系统的研究与淬火无序的周期性介质的相互作用。 这个单一的研究者奖支持一个不寻常的电光效应，与CDW偏振在应用领域的持续调查。这个效应是私家侦探发现的几年前， 这种效应不同于传统的电光效应。它发生在一个宽的光谱范围内（在红外能量低于CDW间隙），发生在非常低的电场（小于0.1 V/cm，对应于需要depin的CDW的字段），并在样品内的空间变化，改变在样品的中心的符号。 该项目的重点将是更全面地描述这种效应，以便更好地了解其基本物理特性。 在这个过程中，增加了解CDW与声子和未凝聚电子的相互作用，以及CDW极化的动力学。 待研究的材料是准一维CDW导体三硫化钽、三硒化铌和钾铋（“蓝青铜”）。 在肯塔基州大学进行的电反射和电透射实验是用可调谐二极管激光器进行的，将辅之以在先进光源上进行的测量，为从事该项目的学生提供广泛的教育经验。通过施加电压改变光学特性的材料被称为电光材料。它们是光通信的基础，因此具有越来越重要的技术意义。 最近，PI在肯塔基州大学的研究小组发现，“电荷密度波”（CDW）导体，即电子密度以一纳米（十亿分之一米）的典型波长振荡的材料，表现出许多非常不寻常的电光特性。 特别地，电磁波的透射率和反射率的电压依赖性变化发生在非常宽的红外光谱范围内。这些变化发生在非常小的电压下（例如，在1 mm长的样品上为0.01 V），并且随着样品内的位置而变化。 该奖项支持一个项目，继续在一些CDW材料中表征这种效应，目的是更好地理解其基本物理和CDW的一般性质。 实验将使用可调谐红外二极管激光器进行，代表这些设备的固态光谱学的少数应用之一。 这些研究将与劳伦斯伯克利国家实验室先进光源的实验相辅相成，为从事该项目的学生提供广泛的教学经验。

Charge-density-wave (CDW) materials in which the CDW can be depinned with a small electric field serve as model systems studies of the interactions of a periodic medium with quenched disorder. This single-investigator award supports the continued investigation of an unusual electro-optic effect, associated with CDW polarization in an applied field. The effect was discovered by the P.I.'s group several years ago. This effect is unlike conventional electro-optic effects. It occurs over a wide spectral range (at infrared energies below the CDW gap), occurs at very low electric fields (less than 0.1 V/cm, corresponding to the fields needed to depin the CDW), and varies spatially within the sample, changing sign in the sample's center. The emphasis of this project will be to more fully characterize the effect with the aim of obtaining a better understanding of its underlying physics. In the process an increased understanding of CDW interactions with phonons and uncondensed electrons, and the dynamics of CDW polarization will be obtained. Materials to be studied are the quasi-one dimensional CDW conductors tantalum trisulfide, niobium triselenide, and potassium molybdate ("blue bronze"). Electro-reflectance and electro-transmittance experiments at the University of Kentucky, carried out with tunable diode lasers, will be complemented with measurements at the Advanced Light Source, providing a broad educational experience for the students working on the project.Materials whose optical properties are modified by application of a voltage are known as electro-optic materials. They are the basis of optical communications and therefore are of increasing technological importance. Recently, the P.I.'s group at the University of Kentucky discovered that "charge-density-wave" (CDW) conductors, materials in which the electron density oscillates with a typical wavelength of one nanometer (one billionth of a meter), exhibit a number of very unusual electro-optic properties. In particular, voltage dependent changes in the transmittance and reflectance of electro-magnetic waves occur over a very wide infrared spectral range. These changes occur at very small voltages (e.g. 0.01 V across a 1 mm long sample), and vary with position within the sample.. This award supports a project to continue characterization of the effect in a few CDW materials, with the goal of better understanding its underlying physics and the properties of CDW's in general. Experiments will be carried out using tunable infrared diode lasers, representing one of the few applications of these devices for solid state spectroscopy. These studies will be complemented with experiments at the Advanced Light Source at Lawrence Berkeley National Laboratory, providing a broad instructional experience for the students working on the project.