HALL-EFFECT IN THE MIXED-STATE OF ND1.85CE0.15CUO4-DELTA

We observe a sign reversal of the Hall resistivity in the mixed state of the n-type superconductor Nd1.85Ce0.15CuO4-delta Such an anomaly, w hich has also been observed earlier in the p-type oxide superconductor s, has been widely attributed to thermoelectric effects, pinning effec ts, or else to complicated band structures. Recently, based on the sys tematics of the sign reversal in a wide class of materials, there have been attempts to explain the anomaly as an intrinsic aspect of the vo rtex motion. The behavior of the Hall resistivity in Nd1.85Ce0.15CuO4- delta serves as a test for some of the models mentioned above. Particu larly, a model based on thermoelectric effects which has been suggeste d to explain the sign reversal in the p-type superconductor YBa2Cu3O7- delta does not predict the sign change in Nd1.85Ce0.15CuO4-delta. The observation of the Hall anomaly in this n-type system supports the ide a that the sign reversal is intrinsically linked to the vortex dynamic s in the flux flow state.