High-temperature superconductivity in bridge and layer compounds

A microscopic model is presented for the structure and superconductivity of $A_x{T}_{1+y}{C}_2$ compounds, where A is a monovalent atom or radical, T is an even-valence transition metal, C is a chalcogenide, and the parameters x and y lie in the ranges 0.1<x≲0.3, 0< y≲0.5. The model explains why the maximum superconducting transition temperature T_S^max is higher than 12°K in bridge compounds with y=0.1, although the maximum value of T_S observed in related layer compounds with y=0.0 is about 6°K.