Positive Hall coefficient observed in single-crystal Nd2−xCexCuO4−δ at low temperatures

Abstract

The Hall coefficient ${\mathit{R}}_{\mathit{H}}$ has been measured in superconducting single crystals of ${\mathrm{Nd}}_{2\mathrm{-}\mathit{x}}$ ${\mathrm{Ce}}_{\mathit{x}}$ ${\mathrm{CuO}}_{4\mathrm{-}\mathrm{\delta }}$(x∼0.15). Although ${\mathit{R}}_{\mathit{H}}$ is sample dependent in sign above ∼100 K, it increases steeply to positive values in all crystals studied below ∼80 K. ${\mathit{R}}_{\mathit{H}}$ remains T (temperature) dependent at 2 K, in contrast to the resistivity ${\mathrm{\rho }}_{\mathit{a}}$ which saturates to a constant below 30 K. Using a two-band model, we account for the observed profiles of ${\mathit{R}}_{\mathit{H}}$ vs T and ${\mathrm{\rho }}_{\mathit{a}}$ vs T. The analysis reveals that the scattering processes for the electronlike and holelike bands have vastly different temperature scales. The hole-scattering rate remains T dependent to 2 K. The question whether the hole or the electron quasiparticles are responsible for the superconductivity in ${\mathrm{Nd}}_{2\mathrm{-}\mathit{x}}$ ${\mathrm{Ce}}_{\mathit{x}}$ ${\mathrm{CuO}}_{4\mathrm{-}\mathrm{\delta }}$ is discussed.