Dirty Superconductivity in the Electron-Doped Cuprate ${\mathrm{Pr}}_{2-x}{\mathrm{Ce}}_x{\mathrm{CuO}}_{4-\delta }$: Tunneling Study

We report a tunneling study between ${\mathrm{Pr}}_{2-x}{\mathrm{Ce}}_x{\mathrm{CuO}}_{4-\delta }$ and lead as a function of doping, temperature, and magnetic field. The temperature dependence of the gap follows the BCS prediction. Our data fit a nonmonotonic $d$-wave order parameter for the whole doping range studied. From our data we are able to conclude that the electron-doped cuprate ${\mathrm{Pr}}_{2-x}{\mathrm{Ce}}_x{\mathrm{CuO}}_{4-\delta }$ is a weak-coupling BCS dirty superconductor.

Figure 1

Conductance vs voltage for the six doping levels of ${\mathrm{Pr}}_{2-x}{\mathrm{Ce}}_x{\mathrm{CuO}}_{4-\delta }$ studied at 1.8 K and zero field (○). At this temperature and field both electrodes are superconducting: note the Pb phonons around 5 and 9 meV. The red solid line is a nonmonotonic $d$-wave fit to the data described in the text.

Figure 2

$\mathrm{\text{Lead}}/{\mathrm{Pr}}_{1.85}{\mathrm{Ce}}_{0.15}{\mathrm{CuO}}_{4-\delta }$ tunneling spectra at representative temperatures (○). The line is a fit using the parameters obtained from Fig. 1, with the gap amplitude [${\Delta }_0(T)$] being the only fitting parameter.

Figure 3

The reduced gap maximum obtained from fits as demonstrated in Fig. 2 plotted vs reduced temperature for ${\mathrm{Pr}}_{1.85}{\mathrm{Ce}}_{0.13}{\mathrm{CuO}}_{4-\delta }$ (□) and ${\mathrm{Pr}}_{1.85}{\mathrm{Ce}}_{0.15}{\mathrm{CuO}}_{4-\delta }$ (○). The dashed line is the BCS universal line.