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

Abstract

A detailed study of the electrical transport properties in high-quality bulk single crystals ${\mathrm{YBa}}_2$ ${\mathrm{Cu}}_3$ ${\mathrm{O}}_7$ has manifested a Kosterlitz-Thouless (K-T)–type transition in the ab plane 0.2 K below the mean-field superconducting transition ($T_c^0$=93.15 K). The c-axis correlation length $l_c$(T=0)≃6 Å and a large two-dimensional effective mass ($m_{\mathrm{ab}}^{\mathrm{*}}$/$m_e$∼10) 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.