  The electrical transport properties of ultrathin YBCO films have been
modified using an electric double layer transistor configuration employing an
ionic liquid. The films were grown on SrTiO3 substrates using high pressure
oxygen sputtering. A clear evolution from superconductor to insulator was
observed in nominally 7 unit cell thick films. Using a finite size scaling
analysis, curves of resistance versus temperature, R(T), over the temperature
range from 6K to 22K were found to collapse onto a single scaling function,
which suggests the the presence of a quantum critical point. However the
scaling failed at the lowest temperatures suggesting the presence of an
additional phase between the superconducting and insulating regimes.
