Study of Planar ${\rm MgB}_{2}/{\rm TiB}_{2}/{\rm MgB}_{2}$ Josephson Junctions Using the Proximity Effect SNS Model

Abstract

Planar MgB <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> /TiB <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> /MgB <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> junctions were fabricated by locally removing MgB <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> within a gap of les 50 nm on a bilayer film of MgB <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> /TiB <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> on SiC substrate using focused ion beam (FIB). Junctions with gaps of different depths were studied. We found that when the gap is too shallow the junction shows a flux-flow behavior, while a too deep gap will result in a junction with no supercurrent. Only junctions with the right gap depth exhibit good resistively-shunted-junction (RSJ) like current-voltage characteristics and excellent ac Josephson effect. The junctions' behavior can be described by the proximity effect superconductor-normal metal-superconductor (SNS) model, suggesting that the Josephson coupling is through the proximity effect in the metallic TiB <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> layer.