Proximity and Josephson effects in microstructures based on multiband superconductors (Review Article)

Emerging in the 1950s, the multiband superconductivity has been considered for a long time as an approximate model in the form of a generalization of the BCS theory to the case of two bands for a more accurate quantitative description of the properties and characteristics of such superconductors as cuprates, heavy fermions compounds, metal boron carbides, fullerides, strontium ruthenate etc. due to their complex piecewise-continuous Fermi surfaces. However the discovery of the multiband structure of the superconducting state in magnesium diboride in 2001 and iron oxypnictides and halides in 2008 led to the appearance of many papers in which effects and different dependences well known for usual one-band s-wave superconductors were re-examined. The main purpose of these studies was to reveal the symmetry type of the order parameter, which provides an important information about the mechanism of Cooper pairing in these superconductors. One of the most effective methods of obtaining information on the symmet...