Torque magnetometry on single-crystal high temperature superconductors near the critical temperature: a scaling approach

TL;DR

This study uses angular-dependent torque measurements on single-crystal high-temperature superconductors near T_c, scaled by the 3D XY model, to analyze universal critical properties and observe a crossover from 3D to 2D behavior influenced by anisotropy.

Contribution

It introduces a scaling approach based on the 3D XY model to analyze torque data, revealing anisotropy effects and a 3D-2D crossover in high-T_c superconductors.

Findings

Scaling function shifts with anisotropy D-2D crossover

Observation of a quasi 2D crossing region (M*, T*)

Enhanced fluctuations in underdoped regime

Abstract

Angular-dependent magnetic torque measurements performed near the critical temperature on single crystals of HgBa_{2}CuO_{4+y}, La_{2-x}Sr{x}CuO_{4}, and YBa_{2}Cu_{3}O_{6.93} are scaled, following the 3D XY model, in order to determine the scaling function dG^{\pm}(z)/dz which describes the universal critical properties near T_{c}. A systematic shift of the scaling function with increasing effective mass anisotropy \gamma = (m_{ab}*/m_{c}*)^{1/2} is observed, which may be understood in terms of a 3D-2D crossover. Further evidence for a 3D-2D crossover is found from temperature-dependent torque measurements carried out in different magnetic fields at different field orientations \delta, which show a quasi 2D "crossing region'' (M*,T*). The occurrence of this "crossing phenomenon'' is explained in a phenomenological way from the weak z dependence of the scaling function around a value z = z*. The "crossing'' temperature T* is found to be angular-dependent. Torque measurements above T_{c} reveal that fluctuations are strongly enhanced in the underdoped regime where the anisotropy is large, whereas they are less important in the overdoped regime.