Composition and structure of the anion layer in the organic superconductor κ′-(ET)2Cu2(CN)3:: Optical study

By means of the methodical optical study of the organic superconductor kappa'-(ET)(2)CU2(CN)(3), its true chemical formula was proven to be kappa-(ET+0.5(1-x))(2)CU2-y-x+CUx+2(CN)(3-2y)[N(CN)(2)]y. In organic materials, this is the first superconducting system with a variety of T-c's. It was obtained from a Mott-insulator Of kappa-(ET)(2)X type by two cooperative phenomena, doping Cu+ --> Cu2+ (X) and exchanging of NC-Cu-CN by NC-N-CN (y), without a major change in the size/symmetry of the anion layer. <Graphics>