Anomalous flux-flow Hall effect: ${\mathrm{Nd}}_{1.85}$${\mathrm{Ce}}_{0.15}$${\mathrm{CuO}}_{4\mathrm{-}\mathit{y}}$ and evidence for vortex dynamics

We report an observation of a sign change in the Hall resistivity ${\mathrm{\rho }}_{\mathit{x}\mathit{y}}$ in the superconducting state of the n-type superconductor ${\mathrm{Nd}}_{1.85}$ ${\mathrm{Ce}}_{0.15}$ ${\mathrm{CuO}}_{4\mathrm{-}\mathit{y}}$. This anomaly in other superconductors has widely been attributed to extrinsic effects, such as pinning or thermoelectric effects, or else to complicated band structures. However, the behavior of the Hall effect in the n-type cuprate ${\mathrm{Nd}}_{1.85}$ ${\mathrm{Ce}}_{0.15}$ ${\mathrm{CuO}}_{4\mathrm{-}\mathit{y}}$ and the systematics of the anomaly in other superconducting materials together provide strong evidence against such models. The data instead indicate that ${\mathrm{\rho }}_{\mathit{x}\mathit{y}}$ reveals an intrinsic property of vortex motion.