Hamburg 2001 – scientific programme

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TT: Tiefe Temperaturen

TT 9: Tunneln und Ordnungsparameter

TT 9.4: Talk

Tuesday, March 27, 2001, 10:15–10:30, H

Microwave measurements of the quasiparticle density and lifetime in Sr₂RuO₄ — •M. A. Hein¹, R. J. Ormeno², A. Sibley², C. E. Gough², and Y. Maeno³ — ¹University of Wuppertal — ²University of Birmingham (UK) — ³Kyoto University (Japan)

We have measured the microwave surface impedance to assess the density and lifetime of quasiparticles of the low-T_c two-dimensional copper-free perovskite superconductor Sr₂RuO₄ above and below T_c. Several high-purity crystals (T_c=1.4K) have been investigated at temperatures T=0.4-20K and frequencies f=4-20GHz using a hollow dielectric resonator. The microwave dissipation in the crystals decreased smoothly as the temperature dropped below T_c, but the microwave penetration length passed through a frequency and purity dependent maximum. This unexpected behaviour can be described by a two-fluid model, which also accounts for a retarded and non-local quasiparticle response. From a comparison between data and model we have extracted a long quasiparticle lifetime, which is in accordance with the high purity of the crystals and DC resistivity data. The derived temperature dependence of the normal fraction of quasiparticles displayed power-law behaviour, which is in contradiction with the existence of a bulk, isotropic energy gap.