New features in the microwave response of YBCO crystals: Evidence for a multi-component order parameter

TL;DR

This study reports new microwave conductivity features in YBCO crystals, revealing evidence for a multi-component order parameter and multiple pairing interactions, challenging the single order parameter assumption.

Contribution

It provides experimental evidence for multi-component superconductivity in YBCO, introducing new features in microwave response data that suggest multiple pairing mechanisms.

Findings

Observation of a third peak in normal conductivity at ~80K

Enhanced pair conductivity below ~65K

Inconsistency with single order parameter models

Abstract

New features are reported in precision measurements of the complex microwave conductivity of high quality $YBa_{2}Cu_{3}O_{6.95}$ crystals grown in $BaZrO_{3}$ crucibles. A third peak in the normal conductivity, $\sigma_{1}(T)$, at around $80K$, and enhanced pair conductivity $\sigma_{2}(T)$ below $\sim 65K$ are observed. The data are inconsistent with a single order parameter, and instead are indicative of multi-component superconductivity. Overall, these results point to the presence of multiple pairing interactions in $YBa_{2}Cu_{3}O_{6.95}$ and also provide a natural explanation to account for the low temperature $35K$ conductivity peak observed in all $YBa_{2}Cu_{3}O_{6.95}$ crystals.