Recent studies of organic molecular solids are highlighted by their complex phase diagram and light-induced phenomena, such as Mott insulator, spin liquid phase, and superconductivity. However, a discrepancy between experimental observation and first-principle calculation on the κ-(BEDT-TTF)2X family inhibits understanding their properties. Here, we revisit the electronic structure of κ-(BEDT-TTF)2Cu2(CN)3 with the recently developed DFT+GOU method to correct the energy level of molecular orbital states in the molecular solid. Our work reveals that the insulating electronic structure of κ-(BEDT-TTF)2Cu2(CN)3 originates from the energy gap between the highest occupied and the lowest unoccupied molecular orbital states of the BEDT-TTF dimers, that are the periodic unit of the molecular solid. We verify that our calculation result provides consistent band gap, optical conductivity, and evolution of the metal-insulator transition as a function of pressure with experimental observations. Especially, the superconducting dome of κ-(BEDT-TTF)2Cu2(CN)3, which originates from the flat band state at the Fermi level, is reproduced. Additionally, we constructed a new low-energy lattice model based on the ability of electronic structure data that can be used to address many-body physics, such as quantum spin liquid and double-holon dynamics. Our provides a deeper understanding of the complex phase diagram and various light-induced phenomena in the κ-(BEDT-TTF)2X family and the other complex organic molecular solids.
@article{arxiv.2412.18088,
title = {Origin of the insulating and superconducting phases in molecular solid $\kappa$-(BEDT-TTF)$_2$Cu$_2$(CN)$_3$},
author = {Dongbin Shin and Fabijan Pavošević and Nicolas Tancogne-Dejean and Michele Buzzi and Emil Viñas Boström and Angel Rubio},
journal= {arXiv preprint arXiv:2412.18088},
year = {2024}
}