THE INFLUENCE OF EXTERNAL BIAS VOLTAGE ON ELECTRICAL-PROPERTIES OF YBA2CU3O7-X METAL POINT-CONTACT INTERFACE

We have investigated a change of electrical properties of YBa2Cu3O7-de lta/metal point contact immediately after its preparation depending on time, temperature as well as external bias voltage. The increase of t he point contact differential resistance in time was experimentally ob served at temperature above 200 K even if no external bias voltage was applied. The low external bias voltage considerably influences the ti me increase of the differential resistance indicating apt important ro le of oxygen diffusion. It is shown on differential characteristics th at for Au,In the parameters of tunneling barrier such as the average h eight and width are constant in time whereas for Al, Pb an evolution o f the tunneling barrier was observed because of oxidation of Al and Pb . Applying of higher bias voltage (up to 1 V) enables the transport of oxygen even below 200 K (down to 4.2 K) and changes the electrical pr oper ties of YBCO/metal point contact interface. The differential char acteristics change their behaviour from that typical for NIS contact w ith strong tunneling barrier to NS contact with a high transparency of the interface. All the above changes are reversible upon changing the bias voltage polarity.