# The importance of direct exchange in Kitaev magnetism

## TL;DR

This paper shows that direct Coulomb exchange may play a key role in Kitaev magnetism, expanding the types of materials where this quantum state can occur.

## Contribution

The study reveals that direct exchange mechanisms, not just indirect ones, are important in Kitaev magnets, suggesting new materials and design principles.

## Key findings

- Direct Coulomb exchange is significant in 5d, 4d, and rare-earth Kitaev–Heisenberg magnets.
- This mechanism suggests new materials may host Kitaev physics.
- It offers new ways to tune the Kitaev interaction strength.

## Abstract

In magnetism research, Kitaev’s honeycomb spin model is one of the revelations of the 21st century: it hosts a quantum spin-liquid ground state that can be described analytically. Current scenarios for the occurrence of bond-dependent magnetic interactions as proposed by Kitaev rely on indirect exchange mechanisms based on intersite electron hopping. Analyzing the wavefunctions of Kitaev magnetic bonds at both single- and multiconfiguration levels, we find however that direct, Coulomb exchange may be at least as important in 5d and 4d  t2g5, 3d  t2g5eg2, and even rare-earth 4f1 Kitaev–Heisenberg magnets. The Coulomb exchange mechanism hints at Kitaev physics in materials that so far were not expected to host it, new ways of tuning the relative strength of the Kitaev interaction, and new design principles for Kitaev spin liquids.