Unconventional transport and superconducting properties in electron-doped cuprates

Abstract

We report a study of transport and magnetic properties of high-quality $c$ axis-oriented superconducting ${\mathrm{T}}^{\ensuremath{'}}$-$R{E}_{2\ensuremath{-}x}$Ce${}_{x}$CuO${}_{4}$ ($RE$ $=$ La, Pr, Nd) thin films grown by molecular beam epitaxy at optimal as well as $x$ $=$ 0.00 doping levels. While the superconducting coherence length ${\ensuremath{\xi}}_{\mathit{GL}}$ decreases from $RE$ $=$ Nd to La, it remains nearly constant as a function of doping. For optimally doped ${\mathrm{T}}^{\ensuremath{'}}$-cuprates, the electronic conductivity is higher than the dopant-free sample, while ${T}_{c}$ is higher for the dopant-free samples for $RE$ $=$ Nd and Pr. We estimated the superconducting penetration depth ${\ensuremath{\lambda}}_{\mathrm{ab}}$ by using a relationship obtained from optical measurements and compared it to the diamagnetic response, which corresponds to the superfluid density ${n}_{s}$. Our data suggest that electron doping increases the superfluid density ${n}_{s}$ significantly, but the pairing interaction is not affected. In the normal state, the temperature dependence of the resistivity was used to deduce the Fermi temperature ${T}_{\mathrm{F}}$, from which we estimated the charge-carrier concentration $n.$ A systematic relationship between $n$, ${n}_{s}$, and the superconducting transition temperature ${T}_{c}$ was not observed. We finally conclude that the superconducting ground state is merely influenced by Ce doping with respect to ${T}_{c}$ and ${\ensuremath{\xi}}_{\mathit{GL}}$ but solely by the $RE$ element.