ELECTRIC-FIELD-INDUCED SUPERCONDUCTIVITY IN AN OVERDOPED CUPRATE SUPERCONDUCTOR

Cuprate superconductors have a low carrier density and therefore their properties can be modified by an electric field. We describe an experiment where we observe field induced superconductivity on the surface of a cuprate material which is overdoped compared to optimal hole doping for maximum T-c. Ca-doped SmBa2Cu3Oy films were grown by molecular beam epitaxy in an ozone beam. Ca doping causes an increase in hole concentration of the SmBa2Cu3Oy and a decrease in T-c from 90K to 50K. BaTiO3 is used as a dielectric across which an electric field is applied. We have observed an increase in T-c of about 1K when a positive voltage is applied.