The Electro-Optic Effect in Charge-Density-Wave Conductors

This individual investigator award funds a project to thoroughly investigate a new electro-optic effect in quasi-one-dimensional charge-density-wave (CDW) conductors. The effect is caused by deformation of the CDW by an applied electric field and is unusual in that it occurs at very small fields (0.1V/cm) and over a very wide infrared spectral range (0-1200 cm-1). This project involves the use of modulation spectroscopy with tunable infrared diode lasers The project is to extend previous measurements of the PI's group, which were for transmittance of infrared light polarized transversely to the conducting chains in the CDW compound K0.3MoO3, to other polarizations, optical constants (e.g. reflectivity), and materials. The research will investigate the fundamental physics of CDW materials, some of the most unusual conductors known, including how the CDW deforms in a field, what new states are associated with CDW motion, and how phonons are affected by this motion. At the same time, the research will probe the utility of CDW materials for electro-optic devices and also represents the first application of tunable infrared diode lasers to solid state spectroscopy. The PI's group will work closely with the laser manufacturer (Laser Components Instrument Group) in interfacing the lasers with an infrared microscope for these studies. The skills the students learn in building equipment, as well as carrying out and interpreting the experiments will aid their future careers, whether they go into industry, academia, or government research. In addition the industrial connection will give the students a direct insight into industrial research. %%% The periodic modulation of the electron density in a crystal is known as a charge density wave (CDW). Under certain conditions, such as an applied electric field, the CDW is able to move, or slide, as a coherent entity through the material. Materials with sliding CDWs exhibit some of the most unusual electronic properties ever observed. Recently, the principal investigator's group discovered that the response of a material to radiation in the infrared range is also affected by CDW sliding. This gives rise to an electro-optic response at much smaller electric fields and over a much wider spectral range than for conventional electro-optic materials. This individual investigator project will extend the previous investigations of the electro-optic response of CDW materials, with the goals of i) improving our knowledge of how the CDW moves and interacts with the crystal, ii) studying how the effect might be utilized in devices, and iii) extending the application of tunable infrared diode lasers to solid state spectroscopy. The manufacturer of the laser (Laser Components Instrument Group) will work closely with the principal investigator's group to optimize this application. The skills the students learn in building equipment, as well as carrying out and interpreting the experiments will aid their future careers, whether they go onto industrial or academic research. In addition the industrial connection will give the students a direct insight into industrial research.