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

TL;DR

This study measures the magnetic penetration depth in Pr$_{2-x}$Ce$_x$CuO$_{4- ext{delta}}$ films, revealing evidence for a nodeless superconducting gap across various doping levels, challenging the expectation of nodal gaps in such materials.

Contribution

It provides experimental evidence for a nodeless superconducting gap in electron-doped cuprates using penetration depth measurements on films grown on buffered substrates.

Findings

$ ext{λ}^{-2}(T)$ is flat at low T, indicating a gap in the density of states.

Minimum superconducting gap ranges from 0.29 to 1.01 times $k_B T_c$.

Films are clean, homogeneous, and exhibit a nodeless gap across doping levels.

Abstract

We report measurements of the inverse squared magnetic penetration depth, $\lambda^{-2}(T)$, in Pr$_{2-x}$Ce$_{x}$CuO$_{4-\delta}$ ($0.115 \leq x \leq 0.152$) 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, $0.124\leq x \leq 0.144$, $\lambda^{-2}(T)$ 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 $0.29\leq\Delta_{\rm min}/k_BT_c\leq1.01$.