Relationship between electrical transport and hole concentration in YBa2Cu3O7−x ultrathin films probed by electric fields

Abstract

The hole concentration in YBa2Cu3O7−x ultrathin films has been changed by electric fields using superconducting field effect transistors. The transistors consisted of YBa2Cu3O7−x/SrTiO3/Au trilayer systems which have been prepared in situ by pulsed laser deposition onto (100) SrTiO3 substrates and patterned by suitable metal masks during the deposition process. The hole concentration change has been determined by measuring the field-induced dielectric polarization of the SrTiO3 dielectric. The relative changes (modulations) of the resistance RDS, the superconducting transition temperature Tc, and the critical current density jc have been studied as a function of the relative change of the hole concentration n. The relationships were found to be linear with coefficients α=1, β=2.5, and γ=3 for the modulations of RDS, Tc, and jc, respectively, within the free carrier model. A quite small hole concentration of n=1×1021 cm−3 could be determined. In the discussion, the possible influence of weak links on the results has been considered.