An excess current in Bi2223-Ag contacts above the critical temperature

In contacts normal metal-superconductor Bi1.6Pb0.4Sr1.8Ca2.2Cu3O10 (Bi2223), the energy gap Delta(T) of the superconductor and the excess current I-exc(T) were measured by means of the Andreev spectroscopy. It is shown that the parameter Delta(T) turns to zero at the superconducting transition temperature of the cuprate, T-c approximate to 110 K, and the dependence Delta(T) follows the BCS theory; at the same time, the excess current I-exc(T) persists up to the temperature T-pair approximate to 180 K, significantly higher than T-c. The result obtained indicates a possible existence in Bi2223 of a wide temperature range T-c < T < T-pair where a condensate of Cooper pairs starts to form. (C) 2013 AIP Publishing LLC.