  A central issue for copper oxides is the nature of the insulating ground
state at low carrier densities and the emergence of high-temperature
superconductivity from that state with doping. Even though this
superconductor-insulator transition (SIT) is a zero-temperature transition,
measurements are not usually carried out at low temperatures. Here we use
magnetoresistance to probe both the insulating state at very low temperatures
and the presence of superconducting fluctuations in La_{2-x}Sr_{x}CuO_{4}(LSCO)
films, for doping levels that range from the insulator to the superconductor
(x=0.03-0.08). We observe that the charge glass behavior, characteristic of the
insulating state, is suppressed with doping, but it coexists with
superconducting fluctuations that emerge already on the insulating side of the
SIT. The unexpected quenching of the superconducting fluctuations by the
competing charge order at low temperatures provides a new perspective on the
mechanism for the SIT.
