First-principles study of a few pnictide superconductors and surface states of a topological insulator

Abstract

Superconductivity is an exciting phenomenon of current flow with zero resistance. Besides the zero resistance, the superconducting material has a few exotic properties: (1) in the presence of the magnetic field from the interior of a superconductor magnetic lines of force are excluded (2) below a characteristic temperature (Tc) superconductivity can be destroyed by the application of external magnetic field which we call type-I superconductors and for type-II superconductors, superconductivity can be partially destroyed with the application of magnetic field H (Hc1<H<Hc2). Following the discovery of superconductivity by Onnes in 1911, a series of superconductors had been discovered and the transition temperature (TC) kept on increasing. More than 2000 materials had been predicted to be superconducting by 1975 and TC rose to 22.3 K with the appearance of Nb3Ge superconductor [1] in 1973. Most successful BCS theory appeared in 1957. With the success of this theory, it was believed that higher transition temperature is not possible without new superconducting mechanism. Already in 1954, Fröhlich proposal [2] for the high temperature superconductivity in charge density wave system and in 1964 Little’s excitonic superconductivity model [3] initialize the possibility of getting high temperature superconductors. In 1975, superconductivity was found in BaPb1-xBixO3 with TC= 13 K [4] which is regarded as the first oxide superconductor.