Magnetic Penetration Depth and Surface Resistance in YBa_2Cu_3O_{7-delta}: New Results for Ultra High Purity Crystals

TL;DR

This study reports on the growth of ultra-high purity YBa_2Cu_3O_{7-delta} crystals and measures their magnetic penetration depth and surface resistance, finding no evidence of a second order parameter component.

Contribution

It provides new experimental results on high purity crystals, challenging recent claims of multiple order parameters in similar materials.

Findings

High purity crystals grown in BaZrO_3 crucibles.

No evidence of second order parameter components.

Observed deviations in some oxygen concentrations but no second transition.

Abstract

We have succeeded in growing very high purity (99.995%) YBa_2Cu_3O_{7-delta} crystals in BaZrO_3 crucibles and have measured Delta-lambda(T) and R_s(T) at 1 GHz in crystals with various oxygen treatments. For an oxygen vacancy level of delta=0.007, Delta-lambda and R_s essentially reproduce our previous results and show no sign of the existence of the two order parameter components as recently reported by Srikanth et al. on BaZrO_3-grown crystals. For other oxygen concentrations, we have in some cases observed deviations from the linear low T dependence of Delta-lambda, but never any sign of a second transition.