ULTRA-HEAVY QUASI-PARTICLES IN METALLIC ND2-YCEYCUO4

The specific heat C(p)(T) and the magnetic susceptibility chi(T) of co mpounds Nd2-yxCeyCuO4, 0 less-than-or-equal-to gamma less-than-or-equa l-to 0.2, were measured in the temperature range from 50 mK to 10 K. A Schottky anomaly in C(p)(T) for Nd2CuO4, resulting from the magnetic splitting of the Nd-4f ground state Kramers doublet due to exchange in teractions with the ordered Cu moments, is broadened upon Ce doping, a nd the maximum is shifted to lower temperatures. In overdoped metallic compounds (y = 0.2), the temperature dependence of C(p)(T) is linear below 300 mK with a large value of the coefficient gamma approximately 4 J/K2 per mole Nd. A constant value of chi(T) in the same temperatur e range and the changes of C(p)(T) induced by an applied magnetic fiel d corroborate the interpretation in terms of a heavy-fermion system-du e to the coupling between Nd moments and conduction electrons at the C u sites.