Search for new materials and techniques for superfluid weak links

Superfluid He-3-flow in channels essentially smaller than the coherence length would be challenging. In this paper, a technique is described which allows the production of almost circularly shaped 10 nm diameter holes in nitrocellulose films of 14 nm thickness. These geometrical dimensions also allow Josephson effect experiments in superfluid He-4 of about 1% superfluid density around temperatures of 0.9999 T-lambda. The hole density in the membranes can be as high as 10(8) cm(-2) which allows one to work with high Josephson currents while at the same time the decoherence effect of vibrations is minimised. Alternative solutions for even smaller holes in several differently designed membranes are discussed.