Fabrication of Bi$_{2}$Sr$_{2}$CaCu$_{2}$O$_{8+x}$ ab-Plane Josephson Junctions by a Focused Helium Ion Beam

Abstract

We report the fabrication and measurement of an ab-plane Josephson junction created in an 80-nm thick thin-film-like exfoliated Bi <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> Sr <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> CaCu <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">8+x</sub> $ single crystal flake. The junctions are formed using ion irradiation from a focused helium ion beam which locally converts the material from a superconductor to an insulator. Current-voltage characteristics show the device to be a weak link with I <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">C</sub> R <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">N</sub> product of 40 μA. The critical current exhibits a well-behaved Fraunhofer pattern with magnetic field applied perpendicular to the film confirming the DC Josephson effect. Simulations reveal a large amount of ion straggle deep into the film which is likely influencing the electrical properties. Combination of these devices with the intrinsic junctions could provide a method for multi-dimensional Josephson devices.