Role of layer packing for the electronic properties of the organic superconductor (BEDT-TTF)2Ag(CF3)4(TCE)

The charge-transfer compound (BEDT-TTF)2Ag(CF3)4(TCE) crystallizes in three polymorphs with different alternating layers: While a phase with a κ packing motif has a low superconducting transition temperature of Tc=2.6K, two phases with higher Tc of 9.5 and 11 K are multilayered structures consisting of α′ and κ layers. We investigate these three systems within density functional theory and find that the α′ layer shows different degrees of charge order for the two κ-α′ systems and directly influences the electronic behavior of the conducting κ layer. We discuss the origin of the distinct behavior of the three polymorphs and propose a minimal tight-binding Hamiltonian for the description of these systems based on projective molecular Wannier functions.