Electrostatic modulation of the superfluid density in an ultrathin La2-xSrxCuO4 film

By capacitively charging an underdoped ultrathin La2-xSrxCuO4 film with an electric field applied across a gate insulator with a high dielectric constant, relative changes of the areal superfluid density ns□ of unprecedented strength were observed in measurements of the film kinetic inductance. Although ns□ appears to be substantially reduced by disorder, the data provide, for the first time on the same sample, direct compelling evidence for the Uemura relation Tcns□(T=0) in the underdoped regime of copper-oxide superconductors. © 2006 The American Physical Society.