Transition from a mixed to a pure d-wave symmetry in superconducting optimally doped YBa$_2$Cu$_3$O$_{7-x}$ thin films under applied fields

TL;DR

This study investigates the evolution of the superconducting order parameter in optimally doped YBa₂Cu₃O₇₋ₓ thin films, revealing a transition from mixed to pure d-wave symmetry under applied magnetic fields and varying temperature.

Contribution

It provides experimental evidence of a temperature-induced transition from mixed to pure d-wave symmetry in high-temperature superconductor thin films.

Findings

Finite energy nodal states observed at low temperature

Order parameter reverts to pure d-wave symmetry above a certain temperature

Transition occurs in films thinner than the London penetration depth

Abstract

We have probed the Landau levels of nodal quasi-particles by tunneling along a nodal direction of (110) oriented YBa$_2$Cu$_3$O$_{7-x}$ thin films with a magnetic field applied perpendicular to the $CuO_2$ planes, and parallel to the film's surface. In optimally doped films and at low temperature, finite energy nodal states are clearly observed in films thinner than the London penetration depth. Above a well defined temperature the order parameter reverts to a pure \emph{d}-wave symmetry.