Probing the High-Tc superconducting state with single electron tunneling.

Alexander Ya. Tzalenchuk, Department of Physics, Chalmers University of Technology, S-412 96 Gothenburg, Sweden, Phone: +46-31-772-3665, Fax: +46-31-772 34 71, e-mail:, WWW:
and A.V.Shubnikov Institute of Crystallography RAS, 117421 Moscow, Russia

We shall present an approach to determine important properties of the superconducting condensate using the methods of single-electron tunneling (SET). Placing an island of an HTS material in a SET device allows to study the very complicated system by fine-tuning the number of electrons in it.
We have fabricated a Coulomb blockade electrometer consisting of an ultrasmall YBa2Cu3O7-
d (YBCO) island coupled to two metal electrodes through a high-resistance native surface tunnel barrier. A third electrode placed near the island was used as an electrostatic gate. Spectra typical for tunneling into the YBCO superconductor were reproducibly measured. At temperatures below 0.5 K the low-bias conductance was suppressed by the Coulomb blockade, which could be periodically varied by the gate potential. An external magnetic field of up to 5 T strongly influenced the transport via the island.