Observation of Weak-Limit Quasiparticle Scattering via Broadband Microwave Spectroscopy of a d-Wave Superconductor
P.J. Turner, R. Harris, Saeid Kamal, M.E. Hayden, D.M. Broun, D.C. Morgan, A. Hosseini, P. Dosanjh, G. Mullins, J.S. Preston, Ruixing Liang, D.A. Bonn, and W.N. Hardy
Phys. Rev. Lett. 90, 237005 (2003)
Preprint: cond-mat/0111353

There has long been a discrepancy between microwave conductivity measurements in high temperature superconductors and the conductivity spectrum expected in the simplest models for impurity scattering in a d-wave superconductor. Here we present a new type of broadband measurement of microwave surface resistance that finally shows some of the spectral features expected for a d_x²-y² pairing state. Cusp-shaped conductivity spectra, consistent with weak impurity scattering of nodal quasiparticles, were obtained in the 0.6-21 GHz frequency range in highly ordered crystals of YBa₂Cu₃O_6.50 and YBa₂Cu₃O_6.99.