A theory of the quantum spin liquid in the hyper-honeycomb metal-organic framework [(C$_2$H$_5$)$_3$NH]$_2$Cu$_2$(C$_2$O$_4$)$_3$ from first principles

TL;DR

This paper develops a first-principles model of a hyper-honeycomb metal-organic framework, revealing a complex magnetic structure with weakly coupled antiferromagnetic chains that explains its low-temperature behavior.

Contribution

It introduces a detailed first-principles-derived Heisenberg model for the hyper-honeycomb metal-organic framework, highlighting the distinct sublattice structures and magnetic interactions.

Findings

Identification of two sublattices with different magnetic properties

Weakly coupled antiferromagnetic chains at low temperatures

Effective Heisenberg model derived from Wannier orbitals

Abstract

We construct a tight-binding model of [(C$_2$H$_5$)$_3$NH]$_2$Cu$_2$(C$_2$O$_4$)$_3$ from Wannier orbital overlaps. Including interactions within the Jahn-Teller distorted Cu-centered $e_g$ Wannier orbitals leads to an effective Heisenberg model. The hyper-honeycomb lattice contains two symmetry distinct sublattices of Cu atoms arranged in coupled chains. One sublattice is strongly dimerized, the other forms isotropic antiferromagnetic chains. Integrating out the strongest (intradimer) exchange interactions leaves extremely weakly coupled Heisenberg chains, consistent with the observed low temperature physics.