Anomalous Low Temperature Behavior of Superconducting Nd(1.85)Ce(0.15)CuO(4-y)

TL;DR

This study investigates the unusual low-temperature behavior of the superconducting properties of Nd(1.85)Ce(0.15)CuO(4-y), revealing paramagnetic effects from Nd3+ ions and supporting an isotropic s-wave pairing symmetry.

Contribution

It demonstrates that the anomalous low-temperature behavior in Nd(1.85)Ce(0.15)CuO(4-y) is due to Nd3+ paramagnetic moments and confirms s-wave pairing after correction for magnetic susceptibility effects.

Findings

Anomalous increase in lambda(T) below 4 K in Nd-based cuprate.

Absence of anomaly in Pr-based cuprate.

Exponential lambda(T) dependence indicating s-wave pairing after correction.

Abstract

We have measured the temperature dependence of the in-plane London penetration depth lambda(T) and the maximum Josephson current Ic(T) using bicrystal grain boundary Josephson junctions of the electron-doped cuprate superconductor Nd(1.85)Ce(0.15)CuO(4-y). Both quantities reveal an anomalous temperature dependence below about 4 K. In contrast to the usual monotonous decrease (increase) of lambda(T) (Ic(T)) with decreasing temperature, lambda(T) and Ic(T) are found to increase and decrease, respectively, with decreasing temperature below 4 K resulting in a non-monotonous overall temperature dependence. This anomalous behavior was found to be absent in analogous measurements performed on Pr(1.85)Ce(0.15)CuO(4-y). From this we conclude that the anomalous behavior of Nd(1.85)Ce(0.15)CuO(4-y) is caused by the presence of the Nd3+ paramagnetic moments. Correcting the measured lambda(T) dependence of Nd(1.85)Ce(0.15)CuO(4-y) for the temperature dependent susceptibility due to the Nd moments, an exponential dependence is obtained indicating isotropic s-wave pairing. This result is fully consistent with the lambda(T) dependence measured for Pr(1.85)Ce(0.15)CuO(4-y).