Doping experiments on YBa_2Cu_3_(7-x) ultrathin films by using electric fields

摘要

The hole concentration of YBa_Cu_3O_(7-x) ultrathin films was changed by electric fields using superconducting field effect transistors. The transistors were composed of YBa_2Cu_3O_(7-x)/SrTiO_3/Au trilayers prepared in situ by pulsed laser deposition on (100) SrTiO_3 substrates and patterned by appropriate metal masks during the deposition process. The hole concentration change was determined by measuring the field-induced dielectric polarization of the SrTiO_3 dielectric. The modulations of the resistance RDS, the superconducting transition temperature T_c and the critical current density j_c were investigated as a function of the relative change of the hole concentration n. The relationships were found to be linear with slopes of a-1, 0 = 2.5 and y = 3 for the modulations of R_(DS), T_c, and j_c, respectively. A hole concentration of n = 1 * 10~(21) cm~3 could be determined. The possible influence of weak links on the results is considered in the discussion.