Volume 78, Number 4, May 2007
Article Number 47003
Number of page(s) 4
Section Condensed Matter: Electronic Structure, Electrical, Magnetic and Optical Properties
Published online 10 May 2007
EPL, 78 (2007) 47003
DOI: 10.1209/0295-5075/78/47003

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

T. Schneider

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

received 14 February 2007; accepted in final form 11 April 2007; published May 2007
published online 10 May 2007

The conflicting observations in the highly anisotropic Bi2Sr2CaCu2O $_{8+\delta }$, 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, $\xi _{c}^{+}/\xi _{c}^{-}=\xi _{c0}^{+}/\xi _{c0}^{-}\simeq 0.45$, between the c-axis correlation length probed above ( $\xi _{c}^{+}$) and below ( $\xi _{c}^{-}$) Tc and the comparatively large anisotropy. The latter leads to critical amplitudes $\xi _{c0}^{\pm }$ which are substantially smaller than the distance between two CuO2 double layers. In combination with $\xi _{c}^{+}/\xi _{c}^{-}\simeq 0.45$ and in contrast to the situation below Tc the c-axis correlation length $\xi _{c}^{+}$ 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.

74.72.-h - Cuprate superconductors (high-Tc and insulating parent compounds) .
74.25.Ha - Superconductivity: Magnetic properties .
64.60.Fr - Equilibrium properties near critical points, critical exponents.

© Europhysics Letters Association 2007