Linear Temperature Variation of the Penetration Depth in YBCO Thin Films

Abstract

We have measured the penetration depth $\hat{I}»(T)$ on $\mathrm{YB}{\mathrm{a}}_2\mathrm{C}{\mathrm{u}}_3{\mathrm{O}}_7$ 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 $\hat{I}»(T)$. In high quality films $\hat{I}»(T)$ exhibits the same linear temperature dependence as single crystals, showing its intrinsic nature, and $\hat{I}»(0)=1750\tilde{\mathrm{A}}$. In a lower quality one, the more usual $T^2$ dependence is found, and $\hat{I}»(0)=3600\tilde{\mathrm{A}}$. This suggests that the $T^2$ variation is of extrinsic origin. Our results put the $d$-wave like interpretation in a much better position.

12 pages, revtex, 4 uuencoded figures