Transport Studies of La sub (2-x) Sr sub x CuO sub 4 Near the Insulator-Metal/Superconductor Transition.

We have measured the temperature-dependent resistivities of a series of samples of La sub (2-x) Sr sub x CuO sub 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.