Tunneling studies of electronic state in high-Tc Bi(2212)-system

The tunnel conductance G(V) at various temperatures was measured for the planar junction fabricated on the cleaved face (001) of Bi2Sr2CaYxCu1.94Zn0.06O8+y (BSCYCZO). When a temperature T decreases, the pseudo-gap (PG) opens at 194 K for x = 0 and at 238 K for x = 0.03, and the superconducting gap (SG) opens at 83 K for x = 0 and at 64 K for x = 0.03. The SG peak was highly symmetric around zero bias both for x = 0 and 0.03. While, the PG peak was highly symmetric around zero bias for x = 0 across 194 K but was strongly suppressed in negative bias for x = 0.03 below T-c = 64 K. Furthermore, the PG was observed to coexist with the SG at a temperature between T-c and 4.2 K for x = 0 and 0.03. This suggests that the PG is not the precursor for superconducting transition. (C) 2003 Elsevier Science B.V. All rights reserved.