Effective Hamiltonian for the electronic properties of the quasi-one-dimensional material Li0.9Mo6O17

TL;DR

This paper develops a minimal effective Hamiltonian for Li0.9Mo6O17, capturing its complex electronic phases including unconventional superconductivity, charge order, and non-Fermi liquid behavior, based on a tight-binding model and extended Hubbard framework.

Contribution

It introduces the simplest effective Hamiltonian model for Li0.9Mo6O17's electronic structure, emphasizing the role of long-range Coulomb interactions and near quarter-filling conditions.

Findings

Proposes a tight-binding model describing ladder-like electronic structure.

Identifies the system as close to one-quarter filling, not half-filling.

Suggests an extended Hubbard model with long-range Coulomb interactions.

Abstract

The title material has a quasi-one-dimensional electronic structure and is of considerable interest because it has a metallic phase with properties different from a simple Fermi liquid, a poorly understood "insulating" phase, and a superconducting phase which may involve spin triplet Cooper pairs. Using the Slater-Koster approach and comparison with published band structure calculations we present the simplest possible tight-binding model for the electronic band structure near the Fermi energy. This describes a set of ladders with weak (and frustrated) inter-ladder hopping. In the corresponding lattice model the system is actually close to one-quarter filling (i.e., one electron per pair of sites) rather than half-filling, as has often been claimed. We consider the simplest possible effective Hamiltonian that may capture the subtle competition between unconventional superconducting, charge ordered, and non-Fermi liquid metal phases. We argue that this is an extended Hubbard model with long-range Coulomb interactions. Estimates of the relevant values of the parameters in the Hamiltonian are given. NMR relaxation rate experiments should be performed to clarify the role of charge fluctuations in Li0.9Mo6O17 associated with the proximity to a Coulomb driven charge ordering transition.