Coherent transport and nonlocality in mesoscopic SNS junctions: anomalous magnetic interference patterns

We show that in ballistic mesoscopic SNS junctions the period of critical current versus magnetic flux dependence (magnetic interference pattern), I-c(Phi), changes continuously and nonmonotonically from Phi(0) to 2 Phi(0) as the length-to-width ratio of the junction grows, or temperature drops. In diffusive mesoscopic junctions the change is even more drastic, with the first zero of I-c(Phi) appearing at 3 Phi(0). The effect is a manifestation of nonlocal relation between the supercurrent density and superfluid velocity in the normal part of the system, with the characteristic scale xi(T) = hv(F)/2 pi k(B)T (ballistic limit) or xi T = root hD/2 pi k(B)T (diffusive limit), the normal metal coherence length, and arises due to restriction of the quasiparticle phase space near the lateral boundaries of the junction. It explains the 2 Phi(0)-periodicity recently observed by Heida et al. [Phys. Rev. B57, R5618 (1998)]. We obtained explicit analytical expressions for the magnetic interference pattern for a junction with an arbitrary length-to-width ratio. Experiments are proposed to directly observe the Phi(0) --> 2 Phi(0) - and Phi(0) --> 3 Phi(0)-transitions. (C) 1999 Academic Press.