Transport studies of La_(2-x)Sr_xCuO_4 near the insulator-metal-superconductor transition

Abstract

We have measured the temperature-dependent resistivities of a series of samples of La_(2-x)Sr_xCuO_4 with 0.02≤x≤0.1 over the temperature range 0.05 K≤T≤300 K. We find the onset of superconductivity as x is increased to be correlated with a substantial drop in the magnitude of the normal-state resistivity. We observe no change, however, in the qualitative shape of the resistivity as the superconducting threshold is crossed. We also find that the low-temperature (T≤8.0 K) resistivities of the least concentrated samples can be described by variable range hopping, with a crossover between Coulomb gap and single-particle behavior occurring as x is increased.

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