Planar Superconductor-Normal-Superconductor Josephson Junctions in MgB2

摘要

Since the discovery of superconductivity in MgB2 considerable progress hasbeen made in determining the physical properties of the material, which arepromising for bulk conductors. Tunneling studies show that the material isreasonably isotropic and has a well-developed s-wave energy gap (∆),implying that electronic devices based on MgB2 could operate close to 30K.Although a number of groups have reported the formation of thin films bypost-reaction of precursors, heterostructure growth is likely to requireconsiderable technological development, making single-layer device structuresof most immediate interest. MgB2 is unlike the cuprate superconductors in thatgrain boundaries do not form good Josephson junctions, and although a SQUIDbased on MgB2 nanobridges has been fabricated, the nanobridges themselves donot show junction-like properties. Here we report the successful creation ofplanar MgB2 junctions by localised ion damage in thin films. The criticalcurrent (IC) of these devices is strongly modulated by applied microwaveradiation and magnetic field. The product of the critical current and normalstate resistance (ICRN) is remarkably high, implying a potential for very highfrequency applications.