Das, M. P.Wilson, B. J.2015-05-282015-05-282043-6262http://hdl.handle.net/1885/13629We begin with an introduction of superconductivity by giving a brief history of the phenomenon. The phenomenological Ginzburg–Landau theory and the microscopic theory of Bardeen, Cooper and Schrieffer are outlined. In view of recently available multi-band superconductors, relevant theories of both types are discussed. Unlike the traditional GL theory an extended GL theory is developed relevant to temperatures below the critical temperature. Superconductivity in a nanosystem is the highlight of the remaining part of the paper. Theories and experiments are discussed to give an interested reader an updated account and overview of what is new in this active area of research.14 pages© 2015 Vietnam Academy of Science & Technologyhttp://www.sherpa.ac.uk/romeo/issn/2043-6254/..."Publisher's version/PDF may be used. On authors' personal website, institutional website, institutional repository or subject-based repository" from SHERPA/RoMEO site (as at 28/05/15)multi-band superconductivityGinzburg-Landau theoryBCS theoryextended GL theorynanosuperconductivity2014-12-0510.1088/2043-6262/6/1/0130012015-12-08