Infrared Studies of Cuprate Superconductors

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This individual investigator award is co-funded by the Department of Energy's Basic Energy Sciences program. It supports a project that will study a wide class of cuprate materials by measuring the optical conductivity over a spectral range from the far infrared, where the superfluid density dominates the response, through intermediate frequencies, from which comes most of the spectral weight of the paired condensate, to the optical range where non-Fermi liquid behavior and charge-transfer excitations are observed. One focus of the project will be effects that suppress the superfluid density, beginning with an attempt to understand the fact that even at optimal doping this quantity is anomalously low. A second focus will be the overdoped materials, in an effort to search for and characterize phase transitions within the superconducting state, and to understand the high-doping superconductor-to-metal transition. Third, the project will investigate the electron-doped side of the phase diagram, where recent experiments near optimal doping have found evidence of d-wave superconductivity. The final focus is to study the effect of a large magnetic field on these materials. This will include an investigation of the superconductor-to-insulator transition that has been observed in high magnetic fields at low temperatures. Students working on this research will be involved with novel materials, sophisticated optical measurements, theories of novel materials, low-temperature techniques, vacuum deposition, transport studies, and methods for analysis of optical data.This individual investigator award is co-funded by the Department of Energy's Basic Energy Sciences program. It supports a project to study of high-transition temperature superconductors using infrared and visible light to measure effects associated with the superconductivity. One unique aspect is the wide range of wavelengths employed; they span almost a factor of 10,000. This wide coverage allows studies of both collective effects of the superconducting electrons, called "the condensate," and also vibrations of the atoms in the crystal and absorptions by the electrons. The experiments address a number of questions of intense current interest aimed at increasing our understanding of the potentially technologically useful high temperature superconductors. Students working on this research become involved with novel materials, sophisticated optical measurements, theories of novel materials, low-temperature techniques, vacuum deposition, transport studies, and methods for analysis of optical data.