Nature of conduction in disordered Nd_2-xCe_xCuO_4-δ films

We have used resistivity and Hall measurements on ion-irradiated thin films of the cuprate superconductor Nd2-xCexCuO4-δ (NCCO) to explore the full range of transport behavior as a function of disorder in this material from superconductivity to variable-range-hopping (VRH) conduction. The cotangent of the Hall angle (cot ΘH) in lightly irradiated samples exhibited a temperature dependence related to that of resistivity, providing support for a recent theory of Varma and Abrahams. The most highly irradiated samples exhibited p(T)∝exp[(To/T)0.5] at low temperatures, evidence of VRH in the presence of a Coulomb gap. The change of the Hall number with disorder and temperature is analyzed in the framework of possible two-carrier conduction in NCCO.