Preparation of n-type YBa2Cu3Oy films by an electrochemical reaction method

We report on the continuous carrier control from holes to the electrons in YBa2Cu3Oy (YBCO) films by an electrochemical reaction method. In this method, the reduction in the hole concentration or the electron doping occurs at room temperature simply by applying a voltage of ~1 V between the YBCO film and the Pt electrode in the electrolyte solution of AC1O4 /polyethylene oxide, where A = K or Cs. When the initial sample is slightly overdoped, a dome-like increase and decrease of Tc and an increase of resistance R and Hall coefficient RH, which correspond to a reduction in the hole concentration to ~1021 cm-3, are observed with increasing voltage or application time. These results suggest that this electrochemical method is a straightforward and effective method for electron doping. Starting with a heavily underdoped sample, which is not superconductive, we succeeded in changing the sign of RH from positive to negative and in rapidly reducing R.