Evidence for a Bulk Complex Order-Parameter in Y0.9Ca0.1Ba2Cu3O7-delta Thin Films

TL;DR

This study measures the penetration depth in overdoped Ca-YBCO thin films, revealing a complex order parameter with a finite gap and temperature-dependent scattering, supporting a mixed d-wave and s-wave symmetry.

Contribution

It provides experimental evidence for a bulk complex order parameter in Ca-YBCO thin films using multiple measurement techniques.

Findings

Order parameter of the form Delta*dx2-y2+i*delta*dxy confirmed

Finite energy gap of approximately 14.5 meV observed

Temperature-dependent scattering rate decrease below 15 K

Abstract

We have measured the penetration depth of overdoped Y0.9Ca0.1Ba2Cu3O7-delta (Ca-YBCO) thin films using two different methods. The change of the penetration depth as a function of temperature has been measured using the parallel plate resonator (PPR), while its absolute value was obtained from a quasi-optical transmission measurements. Both sets of measurements are compatible with an order parameter of the form: Delta*dx2-y2+i*delta*dxy, with Delta=14.5 +- 1.5 meV and delta=1.8 meV, indicating a finite gap at low temperature. Below 15 K the drop of the scattering rate of uncondensed carriers becomes steeper in contrast to a flattening observed for optimally doped YBCO films. This decrease supports our results on the penetration depth temperature dependence. The findings are in agreement with tunneling measurements on similar Ca-YBCO thin films.