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

Physikinstitut, University of Zurich - Winterthurerstrasse 190, 8057 Zurich, Switzerland

Received: 14 February 2007
Accepted: 11 April 2007

Abstract

The conflicting observations in the highly anisotropic Bi₂Sr₂CaCu₂O, evidence 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, , between the c-axis correlation length probed above () and below () T_c and the comparatively large anisotropy. The latter leads to critical amplitudes which are substantially smaller than the distance between two CuO₂ double layers. In combination with and in contrast to the situation below T_c the c-axis correlation length exceeds the distance between two CuO₂ double layers very close to T_c 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.