Phase instability in multi-band superconductors

When a superconductor has multiple bands and there is a phase difference of pi between Delta (1) and Delta (2) where Delta (i) is a gap parameter on a band indexed by i, the junction formed with another superconductor rotates the relative phase between Delta (1) and Delta (2) near the interface to lower the Josephson coupling energy. This means that the order parameter is no longer a real number but is a complex number. This phase-instability is demonstrated with a simple model describing the two-band superconductor in terms of the Gimburg-Landau theory. Due to this effect there is a phase shift between the two bulk superconductors forming the junction. Using a quantum interferometer we will be able to detect this shift experimentally.