Evidence for Kosterlitz-Thouless and 3D-xy critical behavior in Bi2212

TL;DR

This study investigates the critical behaviors in Bi2212, revealing evidence for both Kosterlitz-Thouless and 3D-xy phase transitions through magnetization and superfluid density measurements, highlighting a crossover between 2D and 3D behaviors.

Contribution

It provides experimental evidence for the coexistence of Kosterlitz-Thouless and 3D-xy critical behaviors in Bi2212, elucidating the crossover mechanisms between these phases.

Findings

Observation of 2D-xy behavior below and above T_KT

Absence of KT characteristic in superfluid density near T_KT

Confirmation of 3D-xy critical behavior near Tc

Abstract

We present reversible magnetization data of a high quality Bi2212 single crystal and explore the occurrence of 3D-xy critical behavior close to the bulk transition temperature Tc and of Kosterlitz-Thouless (KT) behavior. Below and above the presumed Kosterlitz-Thouless transition temperature T_KT we observe the characteristic 2D-xy behavior: a downward shift of the crossing point phenomenon towards T_KT as the field is decreased and sufficiently below T_KT the characteristic 2D-xy relationship between the magnetization an the in-plane magnetic penetration depth. In contrast, the measured temperature dependence of the superfluid density does not exhibit the characteristic KT-behavior around the presumed T_KT. The absence of this feature is traced back to the 2D- to 3D-xy crossover setting in around and above T_KT. Invoking the Maxwell relation the anomalous field dependence of the specific heat peak is also traced back to the intermediate 2D-xy behavior. However, close to Tc we observe consistency with 3D-xy critical behavior, in agreement with measurements of the in-plane magnetic penetration depth.