HIGH-TEMPERATURE SUPERCONDUCTIVITY OF SEMI-LOCALIZED 2D ELECTRON SYSTEM WITH CIRCULAR MOLECULAR ORBITS

摘要

It is well known that cuprate-oxide high temperature superconductors are characterized by a 2D d-electron system in the CuO_2 network where the probability amplitude of d electrons extends crosswise from each Cu ion. Recently a new trend of high temperature superconductivity is attracting attention where (ⅰ) non-d electron system seems to be responsible for superconductivity, and (ⅱ) where crystal structure appears to possess ⊥ c a 2D network composed of the inter-connection of circular molecular orbits. In the report of Schoen et al. [1] the surface of fullerene (C_(60)) fcc crystal was hole-doped by field effect, where T-c (max) ≈ 52K was found when ≈ 3 holes exist per 1 molecule and Tc approx > 10K when 3 electrons. The 2D conduction surface is formed by the inter-connection of the circular molecular orbit of each spherical C_(60) molecule. Nagamatsu et al. [2] found that MgB_2 shows superconductivity with T_c ≈ 39K. The crystal structure of MgB_2 is believed to be composed of 2D network of B~- hexagons, which has similarity to the 2D structure of graphite (2D network of C hexagons) except the existence of centripetal attraction of electron by the field of Mg~(2+) ion.