Phase Instability in Multi-band Superconductors

When a superconductor has multiple bands and there is a phase difference of π between Δ 1 and Δ 2 where Δ i is a gap parameter on a band indexed by i , the junction formed with another superconductor rotates the relative phase between Δ 1 and Δ 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 Ginzburg–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.