  We have conducted a highly precise doping controlled experiment on a thin
film of the single layer cuprate Bi2Sr2-xLaxCuOy (x = 0.6), in order to observe
the superconducting insulating transition (SIT). Sr2+/La3+ substitution (x =
0.6) allowed us to start from a doping state in the vicinity of the SIT, which
was further finely-tuned by varying the oxygen content in very small amounts
through a vacuum anneal process. Measurements of the Hall effect at 300K and of
the resistance vs. T, R(T), have been performed after each treatment.
Approaching the SIT from the metallic side, and with decreasing T, R(T)
exhibits a high T metallic behaviour down to a temperature Tmin, followed by a
non metallic increase (dR/dT< 0) up to a maximum at Tp before the
superconducting transition at Tc. This re-entrant behaviour in R(T), commonly
observed in cuprates close to the SIT, is attributed to a phase segregation
phenomenon in the presence of strong electronic correlations and
inhomogeneities. We present our results extracted from R(T) and Hall effect
studies in the region close to the SIT and in the insulating region. A phase
diagram shows the characteristic temperatures versus doping.
