Regensburg 2000 – scientific programme

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TT: Tiefe Temperaturen

TT 15: Grundlegende Experimente zur Supraleitung

TT 15.7: Talk

Wednesday, March 29, 2000, 17:15–17:30, H20

Superconductivity and antiferromagnetism in GdBa₂Cu₃O_7−δ — •M. A. Hein, R. J. Ormeno, C. E. Gough, and G. Yang — Superconductivity Research Group, University of Birmingham, UK

Studying the dynamic interaction between magnetic ordering and pairing helps the understanding of superconductivity in the cuprates. We have measured the surface impedance of GdBa₂Cu₃O_7−δ single-crystals in a hollow sapphire resonator at 10, 15 and 21 GHz between 0.6 K and T_c. Associated with the ordering of the Gd spins, surface resistance and reactance increased markedly below 15 K. Modeling their temperature dependences confirmed the Gd spins to be decoupled from the quasiparticles. Evaluating the experimental data at different frequencies yielded the temperature dependences of quasiparticle conductivity, Cooper pair conductivity, static susceptibility, and Gd spin relaxation time. The conductivity resembles literature data on YBaCuO. The Néel temperature T_N was found to be 2.25 K in accordance with published specific heat data. The relaxation time revealed a strong temperature dependence with different relaxation mechanisms above and below T_N. The results for optimally doped samples (T_c = 93 K) will be compared with recent studies of underdoped crystals (T_c ∼ 45 K).