Artificial grain boundary Josephson junctions-properties and applications

Engineered grain boundary Josephson junctions in YBaCuO were formed on bi-crystal Y-ZrO 2 substrates. Laser deposited films were patterned into micron size microbridges. The authors observed a pronounced correlation between superconducting transport properties of grain boundary junctions and the misorientation angle thetas between the two halves of the bi-crystal. The critical Josephson current I c decreased about four orders of magnitude as thetas was increased from 0 to 45 degrees. Clear microwave and magnetic field responses were observed at 77 K. At this temperature, critical current times normal resistance products, I cR n, of up to 1 mV were measured for low angle grain boundaries and Shapiro steps were observed up to that voltage, DC SQUIDs were fabricated and best performance at 77 K was obtained for thetas=32deg with a 4 micrometer strip width. To utilize the higher I cR n value of a lower thetas, sub-micron junctions have to be developed