Observation of the Kosterlitz-Thouless transition and of vortex fluctuations in superconducting single crystals of Bi-based cuprates

Abstract

We have observed power-law behavior in the current-voltage characteristics of single crystals of ${\mathrm{Bi}}_{2}$${\mathrm{Sr}}_{2}$${\mathrm{Ca}}_{1}$${\mathrm{Cu}}_{2}$${\mathrm{O}}_{8+\mathit{y}}$ and ${\mathrm{Bi}}_{1.6}$${\mathrm{Pb}}_{0.4}$${\mathrm{Sr}}_{2}$${\mathrm{Ca}}_{2}$${\mathrm{Cu}}_{3}$${\mathrm{O}}_{\mathit{x}}$ both in zero and in applied magnetic fields. The observed power-law behavior, V\ensuremath{\propto}${\mathit{I}}^{\mathrm{\ensuremath{\alpha}}(\mathit{T})}$ near the transition with a characteristic Nelson-Kosterlitz jump in the exponent \ensuremath{\alpha}(T) at T=${\mathit{T}}_{\mathit{c}}$ gives evidence for a Kosterlitz-Thouless (KT) transition in wihch vortex-antivortex pairs are dissociated within the superconducting planes. In a magnetic field, the KT transition is suppressed because field-induced vortices induce dissipation and reduce the stability of vortex-antivortex pairs. The interaction of vortex pairs with interlayer flux lines has been discussed.