Microwave Spectroscopy of Thermally Excited Quasiparticles in YBa_2Cu_3O_{6.99}

TL;DR

This study measures the microwave surface impedance of high purity YBa2Cu3O6.99 to analyze the conductivity spectrum of thermally excited quasiparticles, revealing long quasiparticle lifetimes below 20 K and increased scattering above.

Contribution

It provides detailed microwave impedance data across multiple frequencies, highlighting the quasiparticle dynamics and scattering mechanisms in high purity YBa2Cu3O6.99.

Findings

Long quasiparticle lifetimes below 20 K

Rapid increase in scattering above 20 K

Weak impurity scattering in high purity crystals

Abstract

We present here the microwave surface impedance of a high purity crystal of $YBa_2Cu_3O_{6.99}$ 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 $BaZrO_3$-grown crystal used in this study. Above 20 K, the scattering increases dramatically, initially at least as fast as $T^4$.