We report on current-voltage measurements of the zero-field normal-superconducting phase transition in thin films of Pr$_{ 2-x}$Ce$_x$CuO$_{ 4-y}$ as a function of doping. We find that the small size of the critical regime in these materials ($\approx 25$ mK) gives rise to mean-field behavior at the phase transition with a static exponent of $\nu \approx 0.5$ for all dopings (in contrast to hole-doped $\mathrm{ YBa_{ 2}Cu_{ 3}O_{ 7-\delta}}$). We also find mean-field behavior in the dynamic exponent $z$. This indicates that Pr$_{ 2-x}$Ce$_x$CuO$_{ 4-y}$ behaves similarly to conventional superconductors in contrast to other cuprate superconductors. However, as the transition width in our samples decreases, the dynamic critical exponent approaches $z=1.5$, similar to the critical exponent found in hole-doped $\mathrm{ YBa_{ 2}Cu_{ 3}O_{ 7-\delta}}$.
Categories: cond-mat.supr-con