THE INFLUENCE OF BIAS VOLTAGE ON YBA2CU3O7-X METAL POINT-CONTACT INTERFACE/

We have investigated the influence of d.c. bias voltage applied on YBa 2Cu3O7-x/metal point contact interface at 4.2-300 K temperature range. The spontaneous increase in time of the differential resistance of po int contacts considerably depending on d.c. bias voltage, was experime ntally observed at temperature above 200 K. The experimental data are simulated by a one-dimensional out-diffusion model of oxygen in the Cu O chains of YBa2Cu3O7-x (YBCO). The obtained results indicate a change of the surface barrier which oxygen must overcome to leave the YBCO i f a d.c. bias voltage is applied to YBCO/metal-tip contact. This allow s the control of the out-diffusion process of oxygen from the YBCO/met al point contact interface. The application of higher bias voltage (up to 2 V) enables the transport of oxygen, even below 200 K (down to 4. 2 K), and changes the electrical properties of the YBCO/metal point co ntact interface. It is shown that the shape of the differential charac teristics can be changed from a typical NIS contact with a strong tunn elling barrier to an NS contact with a high transparency at the interf ace. These changes are reiterated by changing the bias voltage polarit y. The results indicate the possibility of controlling the electrical properties of the YBCO/metal interface by formation with an external b ias voltage.