Josephson Nanokontakte hergestellt mit einem fokussierten He-Ionenstrahl

09.04.2019 bis 08.04.2022

We propose to explore new types Josephson junctions (JJs) “drawn” by Focused Helium Ion Beam (He-
FIB) into the thin film of cuprate superconductor such as YBCO. He-FIB of the right dose, modifies the crystal structure of YBCO along irradiation line of the thickness ~0.5nm, thus creating a JJs. The main advantages are: (a) one can draw the JJs over the whole chip and in different orientations; (b) by controlling the irradiation dose one can obtain different critical current densities jc within the same chip or JJ; (c) for high irradiation dose the value of jc -> 0 so one can “write” resistive walls, i.e., one can “write” complex circuits without the need of nano-lithography; (d) the resolution of He-FIB 10nm allows to fabricate really tiny nanostructures, e.g., define nano-constrictions using resistive walls, and may be even geometric π or φ JJs, which should have the size of the order of coherence length in a,b-direction; (e) the absence of grain boundaries (and associated faceting) should provide better reproducibility. In addition to JJs drawn into YBCO (demonstrated in preliminary work), we would like to check the applicability of this technique for other superconducting films, e.g., LSCO or LAO.
In three major parts of the proposal we will focus on (a) optimizing the fabrication of the devices from film grows to He-FIB parameters, (b) investigating the fundamental properties of the obtained barriers and JJs and, finally, (c) demonstrating several novel devices with sizes or functionality not achievable up to now.
As a result, we hope to explore the fundamental properties of the Josephson devices made using He-FIB, understand the limits of this new technology and its potential for applications.