Microwave Spectroscopy of Thermally Excited Quasiparticles in YBa₂Cu₃O_6.99
A. Hosseini, R. Harris, Saeid Kamal, P. Dosanjh, J. Preston, Ruixing Liang, W.N. Hardy, and D.A. Bonn
Published in Phys. Rev. B 60, 1349 (1999)

We present here the microwave surface impedance of a high purity crystal of YBa₂Cu₃O_6.99 measured at 5 frequencies between 1 and 75 GHz. This data set reveals the main features of the conductivity spectrum of the thermally excited quasiparticles in the superconducting state. Below 20 K there is a regime of extremely long quasiparticle lifetimes, due to both the collapse of inelastic scattering below T_c and the very weak impurity scattering in the high purity BaZrO₃-grown crystal used in this study. Above 20 K, the scattering increases dramatically, initially at least as fast as T⁴.