Magnetic Flux Periodicity In Mesoscopic Two-band Superconductors

Multiply connected superconductors exhibit macroscopic quantum phenomenathat have far-reaching application. In mesoscopic superconductors which comparableto the penetration depth or the coherence length, the properties of thesuperconductors are strongly influenced by the geometry and size of the sample, thusmany novel quantum effects are induced. Moreover, the discovery of MgB2and,especially, iron pnictides has aroused many interest in the research of multi-bandsuperconductivity. Novel quantum effects would be expected due to the coupling oftwo superconducting bands, in combination with the confinement effect of thesamples and temperature-dependent properties.We investigated the magnetic flux dependence of the superconducting stateevolution and quantum phase transition in mesoscopic two-band superconductingloops by numerically solving the generalized Bogoliubov-de Gennes equationsself-consistently. Main results are summarized as follows:(1) To investigate the magnetic flux dependence of the supercurrent inmesoscopic two-band loops, we introduce an effective multi-band case whichincluding the possible interactions between the two orbitals’ electrons based on asingle-orbital model by assuming on-site attraction for s-wave superconductingparing and solve the equation self-consistently.(2) The magnetic flux dependence of the superconducting state evolution formesoscopic two-band noncircular loops is studied by numerically solving thegeneralized Bogoliubov-de Gennes equations self-consistently. The crossover fromhc/e-to hc/2e-flux periodicity of the current can be controlled by increasing theinterband coupling strength or the temperature. For sufficiently small interbandcoupling, the order parameters of the two bands may exhibit different windingnumbers in narrow flux ranges. Moreover, different patterns of flux-tuned quantumphase transitions between the superconducting state and the resistive/normal state are strongly sensitive to the temperature and the strength of the pairing interaction aswell as the loop geometry.