Critical currents of small Bi2Sr2CaCu2O8+x intrinsic Josephson junction stacks in external magnetic fields

Superconducting critical current of a singleCu2O4plane in aBi2You1, Yurgens2, Winkler3 2005Phys. Rev. B

“…6 have also been seen in several other studies of multi-junction stacks of intrinsic Josephson junctions 29,30,31,32 .…”

Theory ofBi2Sr2CaCu2

“…12 Single crystal Bi2212 consists of a stack of intrinsic Josephson junctions, and low-T measurements of the critical current I c and the normal resistance R n across a single c-axis junction led to I c R n values Ϸ1/3 the Ambegaokar-Baratoff ͑AB͒ result. 10,13,14 This is consistent with nonmetallic and incoherent c-axis transport in Bi2212, [15][16][17] and an s-wave OP. 14 Upon intercalation with HgBr 2 , mesa studies revealed that I c and R n , respectively, decreased and increased by two orders of magnitude, but their product I c R n remained about 1/3 of the AB value.…”

“…7,8 In sharp contrast to the single crystal twist experiments, 4 J c ( 0 ) obtained in this way for the cross-whisker junctions varied substantially with 0 . 7,8 Nevertheless, for the 45°cross-whisker junction in a parallel magnetic field, a Fraunhofer-like diffraction pattern consistent with the long-junction limit was observed for their junction with width 36.7 m and Josephson length J Ϸ3 Ϫ4 m. 8,13 In addition, Shapiro step analysis of the 45°c ross-whisker junction indicated that only first-order tunneling is present. 20 If we assume those results are correct, then the data for the crucially important region 0 Ϸ45°arises from weak first-order tunneling only.…”

“…19 Remarkably, Takano et al observed branch structures in the current-voltage (I-V) characteristics of their crosswhisker junctions at 5 K, indicating that the insulating edge regions of the two whiskers had somehow fused into a mesa structure, 7 consisting of a stack of Josephson junctions. 10,13 By assuming I c of the central Vϭ0 branch corresponded to that of the twist junction and that the junction area was equal to the entire whisker overlap, Takano et al inferred a value for the junction J c for each of their 10-16 samples. 7,8 In sharp contrast to the single crystal twist experiments, 4 J c ( 0 ) obtained in this way for the cross-whisker junctions varied substantially with 0 .…”

“…9 Extensive studies of Bi2212 mesas cut from single crystals established that the central Vϭ0 branch, with the smallest I c , is frequently associated with the junction closest to the current lead, and hence furthest from the mesa center. 13 In addition, the branch with the lowest I c corresponds to the true critical current of the stack. 13 These properties might lead to an overestimate of J c (90°), and an underestimation of J c (60°), for example.…”