Role of layer packing for the electronic properties of the organic superconductor (BEDT-TTF)$_2$Ag(CF$_3$)$_4$(TCE)

TL;DR

This study explores how different layer arrangements in the organic superconductor (BEDT-TTF)$_2$Ag(CF$_3$)$_4$(TCE) affect its electronic properties and superconducting transition temperatures using density functional theory.

Contribution

It identifies the impact of layer packing and charge order on electronic behavior and proposes a minimal tight-binding model for these polymorphs.

Findings

Layer packing influences superconducting transition temperature.

Charge order varies between different polymorphs.

A minimal tight-binding Hamiltonian describes the electronic structure.

Abstract

The charge transfer compound (BEDT-TTF)$_2$Ag(CF$_3$)$_4$(TCE) crystallizes in three polymorphs with different alternating layers: While a phase with a $\kappa$ 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 multi-layered structures consisting of $\alpha'$ and $\kappa$ layers. We investigate these three systems within density functional theory and find that the $\alpha'$ layer shows different degrees of charge order for the two $\kappa$-$\alpha'$ systems and directly influences the electronic behavior of the conducting $\kappa$ 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.