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Keywords:

  • High-temperature superconductors;
  • vortex plasma;
  • superconducting fluctuations;
  • time-domain THz spectroscopy

Abstract

More than one hundred years ago Paul Drude derived the frequency-dependent conductivity σ(o) of a gas of point charges, showing that the width of the spectrum was related to the scattering rate of carriers. Seventy five years later, in the late 1970's and early 1980's, it was recognized that σ(o) of a two-dimensional superconductor above it's transition temperature Tc could be described by the Drude response of interpenetrating gases of electrons and vortices. Here we describe measurements of σ(o) in the high-Tc superconductor system Bi2Sr2Ca1-xDyxCu2O8+δ (BSCCO) using time-domain THz spectroscopy that provide evidence for vortices above Tc. We compare this evidence with results obtained by other probes of fluctuations in cuprate superconductors.