Magnetoresistance in HTSC far above T<sub>c</sub>: fluctuations versus normal-state contributions

W. Lang, G. Heine, W. Liebich, X. L. Wang, X. Z. Wang

We discuss the temperature dependence of the anisotropic magnetoresistance in high temperature superconductors with a focus on the magnetoresistance at temperatures significantly above T/sub c/. Recent results on YBa/sub 2/Cu/sub 3/O/sub 7- delta / thin films and single crystals are analyzed and measurements of the in-plane and out-of-plane magnetoresistance in optimally doped Bi/sub 2/Sr/sub 2/CaCu/sub 2/O/sub 8+x/ single crystals are reported. The in-plane magnetoresistance of both YBa/sub 2/Cu/sub 3/O/sub 7- delta / and Bi/sub 2/Sr/sub 2/CaCu/sub 2/O/sub 8+x/ is positive for magnetic fields oriented perpendicular and parallel to the current. The out-of-plane magnetoresistance of Bi/sub 2/Sr/sub 2/CaCu/sub 2/O/sub 8+x/ is negative from 94 to 180 K. The results are discussed considering the magnetic-field suppression of superconducting fluctuations including the Aslamazov-Larkin and Maki-Thompson terms, the normal-state magnetoresistance of quasiparticles, and the reduction of the quasiparticle density of states due to condensation into superconducting fluctuations. A crossover from fluctuation-induced in-plane magnetoresistance close to T/sub c/ to the quasiparticle effect was found around 1.25 T/sub c/. The out-of-plane magnetoresistance is dominated by the density-of-states contribution. All results indicate that superconducting fluctuations persist up to at least 2T/sub c/.

Electronic Properties of Materials
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Austrian Fields of Science 2012
Materials physics
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