Angular Dependence of the Nonlinear Transverse Magnetic Moment of YBCO in the Meissner state

TL;DR

This study investigates the angular dependence of the nonlinear transverse magnetic moment in YBCO superconductors at very low temperature, finding no expected signatures of d-wave symmetry, which suggests a fully gapped Fermi surface.

Contribution

It provides experimental evidence challenging the predicted angular signatures of d-wave symmetry in YBCO superconductors.

Findings

No signature at angular period 2π/4 observed

Null result implies a non-zero gap at all Fermi surface angles

Results challenge the pure d-wave order parameter predictions

Abstract

The angular dependence of the nonlinear transverse magnetic moment of untwinned high-quality single crystals of optimally doped YBCO have been studied at a temperature of 2.5K using a low frequency AC technique. The absence of any signature at angular period 2\pi/4is analyzed in light of the numerical predictions of such a signal for a pure d-wave order parameter with line nodes. Implications of this null result for the existence of a non-zero gap at all angles on the Fermi surface are discussed.