Linear Temperature Variation of the Penetration Depth in YBCO Thin Films

TL;DR

This study measures the temperature-dependent penetration depth in YBCO thin films, revealing intrinsic linear behavior in high-quality samples and extrinsic effects in lower-quality ones, supporting d-wave pairing symmetry.

Contribution

It provides direct measurements of the absolute penetration depth and its temperature dependence in YBCO thin films, clarifying the intrinsic linear behavior versus extrinsic effects.

Findings

High-quality films show linear $oldsymbol{ ext{T}}$ dependence of $oldsymbol{oldsymbol{ ext{lambda}}(T)}$

Lower-quality films exhibit $oldsymbol{ ext{T}}^2$ dependence, indicating extrinsic effects

Results support d-wave pairing symmetry in YBCO

Abstract

We have measured the penetration depth $\lambda(T)$ on $\rm YBa_{2}Cu_{3}O_{7}$ thin films from transmission at 120, 330 and 510~GHz, between 5 and 50~K. Our data yield simultaneously the absolute value and the temperature dependence of $\lambda(T)$. In high quality films $\lambda(T)$ exhibits the same linear temperature dependence as single crystals, showing its intrinsic nature, and $\lambda(0)=1750\,{\rm \AA}$. In a lower quality one, the more usual $T^2$ dependence is found, and $\lambda(0)=3600\,{\rm \AA}$. This suggests that the $T^2$ variation is of extrinsic origin. Our results put the $d$-wave like interpretation in a much better position.