Spin-orbit coupling in {Mo$_3$S$_7$(dmit)$_3$}

TL;DR

This study investigates the effects of spin-orbit coupling in the molecular crystal {Mo$_3$S$_7$(dmit)$_3$} using relativistic density functional theory, revealing significant intra- and inter-molecular interactions that could lead to topological phases.

Contribution

First-principles analysis of spin-orbit coupling in a molecular crystal, constructing a relativistic Hamiltonian and analyzing its implications for topological phases.

Findings

Both intra- and inter-molecular spin-orbit couplings are significant.

Intermolecular spin-orbit interactions can induce quantum spin-Hall and topological insulator phases.

A long-range relativistic single electron Hamiltonian was derived from first principles.

Abstract

Spin-orbit coupling in crystals is known to lead to unusual direction dependent exchange interactions, however understanding of the consequeces of such effects in molecular crystals is incomplete. Here we perform four component relativistic density functional theory computations on the multi-nuclear molecular crystal {Mo$_3$S$_7$(dmit)$_3$} and show that both intra- and inter-molecular spin-orbit coupling are significant. We determine a long-range relativistic single electron Hamiltonian from first principles by constructing Wannier spin-orbitals. We analyse the various contributions through the lens of group theory. Intermolecular spin-orbit couplings like those found here are known to lead to quantum spin-Hall and topological insulator phases on the 2D lattice formed by the tight-binding model predicted for a single layer of {Mo$_3$S$_7$(dmit)$_3$}.