YBCO超薄膜における電界効果

抄録

We have studied electric field effects on resistance and superconducting transition temperature of YBa₂Cu₃O_7-δ (YBCO) using a heterostructure of Ag/BaTiO₃(200nm)/SrTiO₃(1.5nm)/YBCO (n-unit cells: n=10, 6, 2)/SrTiO₃(substrate). The application of a negative gate voltage, V_gate' to the Ag electrode lowered the resistance of YBCO, while a positive V_gate having the opposite effect. The relative change in the normal state resistance ΔR/R, where ΔR is the field-induced change of resistance and R is the resistance at V_gate=0V, was well explained by the field-induced change of carrier density. ΔR/R at V_gate=1V remained constant above T₀ at which the gradient dR/dT takes a maximum value. The field effect on the mean field transition temperature was found to be weaker than that on resistance.