Progressive evolution of tunneling characteristics of in situ fabricated intrinsic Josephson junctions in Bi 2 Sr 2 CaCu 2 O 8 + δ single crystals

Stacks of a few intrinsic tunnel junctions were microfabricated on the surface of ${\mathrm{Bi}}_{2}{\mathrm{Sr}}_{2}{\mathrm{CaCu}}_{2}{\mathrm{O}}_{8+\ensuremath{\delta}}$ single crystals. The number of junctions in a stack was tailored by progressively increasing the height of the stack by ion-beam etching, while its tunneling characteristics were measured in situ in a vacuum chamber for temperatures down to $\ensuremath{\sim}13 \mathrm{K}.$ Using this in situ etching/measurements technique in a single piece of crystal, we systematically excluded any spurious effects arising from variations in the junction parameters and made clear analysis on the following properties of the surface and inner conducting planes. First, the tunneling resistance and the current-voltage curves are scaled by the surface junction resistance. Second, we confirm that the reduction in both the gap and the superconducting transition temperature of the surface conducting plane in contact with a normal metal is not caused by the variation in the doping level, but is caused by the proximity contact. Finally, the main feature of a junction is not affected by the presence of other junctions in a stack in a low-bias region.