Effects of junction geometry in crossover temperature to macroscopic quantum tunneling regime of intrinsic Josephson junctions

We investigated the phase dynamics of long intrinsic Josephson junctions, which were fabricated on a narrow bridge structure of Bi2Sr2CaCu2Oy (Bi-2212) single crystals by using a focused ion-beam etching. We measured the probability distribution of the switching events from the zero-voltage state for two types of junction geometry. One is a junction where the bridge width (L-1) is larger than the Josephson penetration depth, lambda(J), and the distance between two slits (L-2) is comparable to lambda(J), while the other is a junction where L-1 is comparable to lambda(J) and L-2 is larger than lambda(J). We found that a crossover temperature from the thermally activated regime to the macroscopic quantum tunneling regime was quite different between the two types of junction geometry. We discuss the observed behavior in terms of an edge effect in long Josephson junctions dependent on the junction geometry. (C) 2011 Elsevier B.V. All rights reserved.