Two-Dimensional Fluctuations Close to the Zero-Field Transition of Bi_2Sr_2CaCu_2O_8

TL;DR

This study investigates two-dimensional fluctuations near the zero-field transition in Bi2Sr2CaCu2O8, revealing signatures of 2D ordering and universal screening length behavior consistent with Kosterlitz-Thouless theory.

Contribution

It provides experimental evidence of 2D-ordering and universal screening length at the transition, supporting the applicability of Kosterlitz-Thouless theory to high-temperature superconductor films.

Findings

Universal screening length at Tc matches Kosterlitz-Thouless prediction.

Signatures of 2D-ordering observed in ac-conductivity measurements.

Long-range superconductivity nucleates via vortex string binding.

Abstract

The ac-conductivity along the CuO$_2$-layers of epitaxial films and single crystals of thicknesses 0.2$\mu$m$\leq L_z \leq130\mu$m reveals clear signatures for 2D-ordering. In particular, at $T_c$ the screening length assumes the universal value $L_z\Lambda_{T_c}/2\nu_s$ predicted by the Kosterlitz-Thouless theory, which indicates that binding of long vortex strings nucleates long-range superconductivity in the present samples containing up to $10^5$ CuO$_2$-layers. Several details of the order-parameter dynamics remain unexplained.