On the occurrence of Berezinskii-Kosterlitz-Thouless behavior in highly anisotropic cuprate superconductors

TL;DR

This paper investigates the conditions under which Berezinskii-Kosterlitz-Thouless (BKT) behavior appears in highly anisotropic cuprate superconductors, revealing a narrow temperature window where 2D fluctuations dominate due to weak interlayer coupling.

Contribution

It clarifies the emergence of BKT behavior in cuprates by linking anisotropy and correlation length ratios to observable 2D fluctuation regimes.

Findings

BKT behavior appears near Tc in highly anisotropic cuprates.

The ratio of c-axis correlation lengths influences the fluctuation regime.

A narrow temperature window exists where 2D fluctuations dominate.

Abstract

The conflicting observations in the highly anisotropic Bi2Sr2CaCu2O8+x, vidence for BKT behavior emerging from magnetization data and smeared 3D-xy behavior, stemming form the temperature dependence of the magnetic in-plane penetration depth are traced back to the rather small ratio, gsic+/gsic-=0.45, between the c-axis correlation length probed above (+) and below (-) Tc, and the comparatively large anisotropy. The latter leads to critical amplitudes gsic0+,-which are substantially smaller than the distance between two CuO2 double layers. In combination with gsic+/gsic-=0.45 and in contrast to the situation below Tc the c-axis correlation length gsic exceeds the distance between two CuO2 double layers very close to Tc only. Below this narrow temperature regime where 3D-xy fluctuations dominate, there is then an extended temperature regime where the units with two CuO2 double layers are nearly uncoupled so that 2D thermal fluctuations dominate and BKT features are observable.