Modifications of the Meissner screening profile in YBa${}_2$Cu${}_3$O${}_{7-\hat{I}´}$ thin films by gold nanoparticles

Abstract

Adding Au nanoparticles to YBa${}_2$Cu${}_3$O${}_{7-\hat{I}´}$ thin films leads to an increase of the superconducting transition temperature $T_{\mathrm{c}}$ and the critical current density $j_{\mathrm{c}}$. While the higher $j_{\mathrm{c}}$ can be understood in terms of a stronger pinning of the flux vortices at the Au nanoparticles, the enhanced $T_{\mathrm{c}}$ is still puzzling. In the present study, we determined the microscopic magnetic penetration profiles and the corresponding London penetration depths $\hat{I}{»}_{\mathrm{L}}$ in the Meissner state of optimally doped YBa${}_2$Cu${}_3$O${}_{7-\hat{I}´}$ thin films with and without Au nanoparticles by low-energy muon spin rotation. By Rutherford backscattering spectrometry, we show that the Au nanoparitcles are distributed over the whole thickness of the thin-film samples. The superfluid density $n_{\mathrm{s}}\propto 1/\hat{I}{»}_{\mathrm{L}}^2$ was found to increase in the films containing Au nanoparticles. We attribute this increase of $n_{\mathrm{s}}$ to a reduction of the defect density possibly due to defect condensation at the Au nanoparticles.

5 pages, 5 figures