9510353 Orenstein The optical response of high-Tc cuprate superconductors has been the subject of intense investigations since their discovery. It appears that a consistent picture of the responses, from microwave to infrared is finally emerging. However, the understanding that has been achieved is largely confined to zero magnetic field. The proposed research seeks to develop a thorough understanding of the optical response in the vortex-state which arises in response to magnetic field. The study focuses on the terahertz frequency range, which is the crucial one for vortex dynamics in the cuprates because it corresponds to the gap for quasi particle excitations in the vortex core. The key experimental tool is terahertz time-domain spectroscopy, which is the most successful approach to measuring broad band response of the media in the spectral range between the microwave and infra-red domains. In this technique the complex response function is measured directly by resolving the transmission coefficient of nearly-single-cycle picosecond electric field pulses. These pulses are generated and detected optoelectronically through the use of a femtosecond mode- locked laser. %%% The spectacular property of superconductors is the vanishing of the dc resistance. However, above zero frequency, superconductors develop measurable resistance, whose properties are a distinguishing feature of superconductivity in different materials. The resistivity of high temperature cuprate superconductors in zero applied magnetic field, from microwave to visible frequencies, has been studied intensively. This project investigates the fundamentally and technologically important regime of under magnetic field. The proposal seeks to develop a thorough understanding of the response of cuprate superconductors in the "vortex state" which arises in the presence of large magnetic field. The research focus es on the terahertz region of the spectrum, which is the crucial range for the cuprates, and uses a powerful new spectroscopic tool, terahertz time-domain spectroscopy. A broad range of high quality films will be synthesized and investigated . The results will test and stimulate theoretical work, which is evolving rapidly as evidence emerges for unconventional origins of superconductivity in HTS. ***
