Anomalous low temperature behavior of superconducting Nd1.85Ce0.15CuO4-y

We have measured the temperature dependence of the in-plane London penetration depth lambda(ab)(T) and the maximum Josephson current I-c(T) using bicrystal grain boundary Josephson junctions of the electron-doped cuprate superconductor Nd1.85Ce0.15CuO4-y. In contrast to the usual monotonous decrease (increase) of lambda(ab)(T) [I-c(T)] with decreasing temperature, lambda(ab)(T) and I-c(T) are found to increase and decrease, respectively, with decreasing temperature below 4 K. We attribute this anomalous behavior to the presence of the Nd3+ paramagnetic moments. Correcting the measured lambda(ab)(T) dependence for the temperature dependent susceptibility due to the Nd moments, an exponential dependence is obtained indicating isotropic s-wave pairing.