In-plane transport properties of single-crystal ${\mathit{R}}_{2\mathrm{-}\mathit{x}}$${\mathrm{Ce}}_{\mathit{x}}$${\mathrm{CuO}}_{4\mathrm{-}\mathit{y}}$ (R=Nd,Sm)

We have investigated the in-plane transport properties of high-quality crystals of ${\mathit{R}}_{2\mathrm{-}\mathit{x}}$ ${\mathrm{Ce}}_{\mathit{x}}$ ${\mathrm{CuO}}_{4\mathrm{-}\mathit{y}}$ (R=Nd,Sm) prepared over a range of Ce contents x. We find the Hall coefficient ${\mathit{R}}_{\mathit{H}}$ is uniformly negative in superconducting (x near 0.15) and underdoped crystals, indicating electron conduction in the ${\mathrm{CuO}}_2$ planes, and becomes positive at large doping (x∼0.2). The in-plane resistivity remains metallic over this range and decreases monotonically as x increases, consistent with an increasing carrier density. These data confirm results on ceramic samples and demonstrate that electron doping in the T’-phase superconductors and hole doping in the T-phase systems affect transport in the same way.