Systematics of two-component superconductivity in $YBa_{2}Cu_{3}O_{6.95}$ from microwave measurements of high quality single crystals

TL;DR

This study uses microwave measurements on high-quality YBCO crystals to reveal multiple superconducting components, including a new normal conductivity peak at 80K and additional pairing below 65K, indicating complex multi-gap behavior.

Contribution

The paper provides the first systematic microwave analysis revealing multiple superconducting components and new normal conductivity features in YBCO crystals, challenging single-gap models.

Findings

Discovery of a new normal conductivity peak at ~80K.

Evidence of additional pairing below 65K.

Correlation of the 80K peak with inelastic scattering rate.

Abstract

Systematic microwave surface impedance measurements of YBCO single crystals grown in $BaZrO_3$ crucibles reveal new properties that are not directly seen in similar measurements of other YBCO samples. Two key observations obtained from complex conductivity are: a new normal conductivity peak at around 80K and additional pairing below 65K. High pressure oxygenation of one of the crystals still yields the same results ruling out any effect of macroscopic segregation of O-deficient regions. A single complex order parameter cannot describe these data, and the results suggest at least two superconducting components. Comparisons with model calculations done for various decoupled two-component scenarios (i.e. s+d, d+d) are presented. Systematics of three single crystals show that the 80K quasiparticle peak is correlated with the normal state inelastic scattering rate. Close to Tc, the data follow a mean-field behavior. Overall, our results strongly suggest the presence of multiple pairing temperature and energy scales in $YBa_{2}Cu_{3}O_{6.95}$.