THE CURRENT PHASE RELATION OF AN ADJUSTABLE SUPERCONDUCTING POINT-CONTACT WITH BALLISTIC CONDUCTIVITY

A superconducting ring with a very small selfinductance and interrupte d by a mechanically controllable breakjunction is cut out of thin niob ium foil using lasercutting techniques. The current phase relation is determined by measuring the self-induced flux as a function of applied flux. The current phase relations show at low temperatures a clear no n-sinusoidal behaviour with a maximum in the self-induced flux at phas e differences between pi/2 and pi over the contact in accordance with the theory for ballistic point contacts developed almost two decades a go.