Role of layer packing for the electronic properties of the organic superconductor (BEDT-TTF)_2Ag(CF_3)_4(TCE)

摘要

The charge-transfer compound (BEDT-TTF)_2Ag(CF_3)_4(TCE) crystallizes in three polymorphs with different alternating layers: While a phase with a k packing motif has a low superconducting transition temperature of T_c = 2.6 K, two phases with higher T_c of 9.5 and 11 K are multilayered structures consisting of α' and k 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 k-α' systems and directly influences the electronic behavior of the conducting k 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.