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Session O10 - Josephson Junctions and SQUIDS II.
MIXED session, Thursday afternoon, March 21
Room 230, America's Center
In a quantum interference tunneling experiment with a trictrystal junction reported by J. R. Kirtley et. al. [ Nature, 373, 225 (1995) ] the half-integer quantum flux h/4e was observed. We propose an explanation for the existence of half-integer quantum flux in a multi-junction tunneling experiment based on the mixed-charge superconductivity mechanism proposed earlier [K.W.Wong and R.L.Davidchack, Phys. Lett. A 208, 171 (1995)]. In a mixed-charge superconducting state, because of the coupling of charges with opposite signs, a \pi phase shift between the current components is introduced into the expression for the current density. In order to preserve gauge invariance of the expression, another \pi shift is required across the junctions. Therefore, the measured flux quantum can be half the total unit flux. We calculate the optimal geometry of the tricrystal junction and obtain a very good agreement with the experiment. Finally, if our model is correct, half-integer quantum flux can also be observed in a penta-junction, for which we propose an optimal geometry.
