3D XY and lowest Landau level fluctuations in deoxygenated YBCO thin films

TL;DR

This study investigates vortex melting and fluctuation regimes in deoxygenated YBCO thin films, revealing complex scaling behaviors and the transition between 3D XY and lowest Landau level regimes under varying magnetic fields.

Contribution

It demonstrates the coexistence of 3D XY and glass scaling regimes and introduces a lowest Landau level analysis for low-temperature vortex fluctuations.

Findings

Field-independent glass exponents describe vortex melting transition.

3D XY exponents observed at low fields with smaller-than-expected dynamic exponent.

Lowest Landau level analysis provides T_{c2}(H) with positive curvature at low T_g.

Abstract

Conductivity measurements reflect vortex solid melting in YBCO films. Field-independent glass exponents nu_g=1.9 and z_g=4.0 describe the transition T_g(H) for 0<H<26 T. At low fields, 3D XY exponents nu_{XY}=0.63 and z_{XY}=1.25 are also observed, with z_{XY} smaller than expected. These compete with glass scaling according to multicritical theory. A predicted power-law form of T_g(H) is observed for 0.5T_c<T_g<T_c. For T_g<0.5T_c, 3D XY scaling fails, but a lowest Landau level analysis becomes possible, obtaining T_{c2}(H) with positive curvature.