The Effect of Thermodynamic Fluctuations on the Properties of Untwinned Crystals of YBa2Cu3O1−δ
Thermodynamic fluctuations cause small regions of a sample to enter the superconducting state as the temperature approaches Tc from above. Conversely, small regions fluctuate into the normal state below Tc. We review the value of measuring fluctuation effects and the types of measurements that have been made. Conductivity and Hall-effect data are presented for an untwinned crystal of YBa2Cu3O7−δ . The data are analyzed to determine how well they are fitted by the three-dimensional theories of Aslamazov and Larkin and of Maki and Thompson (for the conductivity) and of Fukuyama, Ebisawa, and Tsuzuki (for the Hall effect). We find good qualitative fits to these theories as T approaches Tc, which is the temperature range where these theories are applicable. Quantitatively, however, there is difficulty in matching the data to the theory. For our low resistivity, untwinned YBa2Cu3O7−δ crystal, the fit to the theory would surprisingly indicate that the Maki-Thompson term dominates the Aslamazov-Larkin term in the Hall effect near Tc.
KeywordsHall Effect Coherence Length Superconducting State Conductivity Sample Dimensional Crossover
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