Quasi-two-dimensional phase fluctuations in bulk superconducting YBa2Cu3O7 single crystals

A detailed study of the electrical transport properties in high-quality bulk single crystals YBa2Cu3O7 has manifested a Kosterlitz-Thouless (K-T)type transition in the ab plane 0.2 K below the mean-field superconducting transition (Tc0=93.15 K). The c-axis correlation length lc(T=0)6 A and a large two-dimensional effective mass (mab*/me10) of the supercarrier are estimated based on the K-T theory. The large effective mass suggests strong electron-electron correlations for the supercarriers confined in a quasi-two-dimensional sheet. © 1989 The American Physical Society.