Anisotropy in the helicity modulus of a quantum 3D XY-model: application to YBCO

TL;DR

This study investigates the anisotropic helicity moduli in a quantum 3D XY-model of YBCO, revealing temperature dependencies and anisotropic behavior that challenge experimental observations.

Contribution

It provides a variational analysis of the helicity moduli in an anisotropic quantum 3D XY-model for YBCO, highlighting discrepancies with experimental data.

Findings

Both ab-plane and c-axis helicity moduli vary as T^4 at zero temperature.

The c-axis helicity modulus decreases faster with temperature than the ab-plane.

Results disagree with experimental measurements on high-quality YBCO samples.

Abstract

We present a variational study of the helicity moduli of an anisotropic quantum three-dimensional (3D) XY-model of YBCO in superconducting state. It is found that both the ab-plane and the c-axis helicity moduli, which are proportional to the inverse square of the corresponding magnetic field penetration depth, vary with temperature T as T to the fourth power in the zero temperature limit. Moreover, the c-axis helicity modulus drops with temperature much faster than the ab-plane helicity modulus because of the weaker Josephson couplings along the c-axis compared to those along the ab-plane. These findings are in disagreement with the experiments on high quality samples of YBCO.