Magnetic Penetration Depth Measurements of Pr${}_{2-x}$Ce${}_x$CuO${}_{4-\delta }$ Films on Buffered Substrates: Evidence for a Nodeless Gap

Abstract

We report measurements of the inverse squared magnetic penetration depth, ${\lambda }^{-2}(T)$, in Pr${}_{2-x}$Ce${}_x$CuO${}_{4-\delta }$ ($0.115\le x\le 0.152$) superconducting films grown on SrTiO${}_3$ (001) substrates coated with a buffer layer of insulating Pr${}_2$CuO${}_4$. ${\lambda }^{-2}(0)$, $T_c$ and normal-state resistivities of these films indicate that they are clean and homogeneous. Over a wide range of Ce doping, $0.124\le x\le 0.144$, ${\lambda }^{-2}(T)$ at low $T$ is flat: it changes by less than 0.15% over a factor of 3 change in $T$, indicating a gap in the superconducting density of states. Fits to the first 5% decrease in ${\lambda }^{-2}(T)$ produce values of the minimum superconducting gap in the range of $0.29\le {\Delta }_{\min }/k_B{T}_c\le 1.01$.

4 pages 5 figures