Superconducting state of very thin Pd films deposited on a diluted insulating EuxSr1−xS ferromagnet

Abstract

The electronic transport in very thin Pd films deposited on insulating Eu${}_{x}$Sr${}_{1\ensuremath{-}x}$S ($0\ensuremath{\leqslant}x\ensuremath{\leqslant}1$) is investigated. The temperature dependent resistance $R(T)$ of films with ${d}_{\mathrm{Pd}}\ensuremath{\geqslant}14$ nm shows metallic behavior and a logarithmic increase toward low temperatures characteristic of (anti-)localization and electron-electron interaction effects also observed for Pd films on Si(111). Films with ${d}_{\mathrm{Pd}}=7$ nm are superconducting below a transition temperature ${T}_{c}$ which decreases with increasing Eu concentration from ${T}_{c}=0.9$ K for $x=0$ to ${T}_{c}l50$ mK for $x=1$. The origin of superconductivity in the thin Pd films is presumably due to the formation of an interfacial Pd-S alloy and/or to a charge transfer at the Pd/Eu${}_{x}$Sr${}_{1\ensuremath{-}x}$S interface. The decrease of ${T}_{c}$ vs $x$ is attributed to the magnetic pair breaking of the ferromagnetic Eu${}_{x}$Sr${}_{1\ensuremath{-}x}$S underneath. The $R(T)$ behavior of films with ${d}_{\mathrm{Pd}}\ensuremath{\geqslant}10$ nm suggests that these are not superconducting or have a strongly reduced ${T}_{c}$ presumably due to the proximity effect of the nonsuperconducting S-free upper part of the Pd film.