Low-temperature normal state of Bi-2201 in a wide doping range: Where doesthe metal to insulator crossover take place?

By suppressing the superconductivity with 60-T pulsed magnetic fields, the in-plane normal-state resistivity rho (ab) is measured down to 0.5 K in Bi2 Sr2-xLaxCuO6+delta single crystals with varying carrier concentration. It i s observed that a metallic behavior (d rho (ab)/dT greater than or equal to 0) gradually changes to an insulating one (d rho (ab)/dT < 0) with decreas ing carrier concentration and that this crossover takes place in the underd oped region, not at the optimum doping. This result is notably distinct fro m that reported for La2-xSrxCuO4 or for Pr2-xCexCuO4+<delta>, indicating th at the metal-to-insulator crossover in cuprates is not universally associat ed with the optimum doping.