Josephson current suppression in three-dimensional focused-ion-beam fabricated sub-micron intrinsic junctions

Abstract

We have fabricated intrinsic Josephson junction arrays in Tl 2 Ba 2 CaCu 2 O 8 thin films using three-dimensional focussed ion-beam milling. We have measured the dependence of the switching current density of these arrays at 4.2 K upon the junction cross-sectional area. There is strong suppression of the switching current density for junctions of area less than 1 m 2 , the current extrapolating to zero at an area of 0.25 m 2. We discuss the roles of gallium ion implantation and both thermal and quantum fluctuations in this current suppression.

Investigation of critical current density of submicron intrinsic Josephson junctions of Bi2Sr2CaCu2O8 + δat 30 K

“…The spacing between these elementary IJJs is about 1.5 nm. The number of elementary IJJs (N = z/1.5) can be calculated from the height (z) of the stack [14,15]. Therefore, the J24 stack has approximately 130 elementary IJJs.…”

“…For further verification, we used equation ( 1) to analyze our data. According to this equation in the presence of QFs, the value of J c drops exponentially as [7,15] 6 : 5 The value of E J is calculated using the unfluctuated critical current density (J c• ) and presented in table 1. The value of J c , shown in table 1, is the measured value of critical current density and used in figure4.…”

Critical-current suppression in sub-micron intrinsic Josephson junction arrays

“…We now briefly discuss three mechanisms for the suppression of the switching current in sub-micron intrinsic junctions: gallium ion implantation, thermal fluctuations and quantum fluctuations. A more detailed discussion is given elsewhere [10]. During focussed ion-beam milling, gallium ions are implanted into all four sidewalls of our junction stack up to some distance d imp .…”

“…In Ref. [10], we used gallium ion-milling to sequentially reduce the width of a TBCCO thin-film track. We observed a linear decrease in the room-temperature conductance and inferred that d imp = 90 nm .…”