Role of Hydrogen in the spin-orbital-entangled quantum liquid candidate H$_3$LiIr$_2$O$_6$

TL;DR

This study explores how hydrogen's position and isotopic substitution influence magnetic interactions in H$_3$LiIr$_2$O$_6$, a candidate quantum spin liquid, highlighting the sensitivity of its magnetic properties to microstructure and stoichiometry.

Contribution

The paper combines density functional theory and exact diagonalization to analyze hydrogen's role in magnetic interactions, revealing the impact of bond symmetry and isotopic substitution on magnetic phases.

Findings

Hydrogen bond geometry affects local magnetic couplings.

Hydrogen zero-point fluctuations likely keep bonds symmetrical.

Isotopic substitution and disorder destabilize magnetic interactions.

Abstract

Motivated by recent reports of H$_3$LiIr$_2$O$_6$ as a spin-orbital-entangled quantum liquid, we investigate via a combination of density functional theory and non-perturbative exact diagonalization the microscopic nature of its magnetic interactions. We find that while the interlayer O-H-O bond geometry strongly affects the local magnetic couplings, these bonds are likely to remain symmetrical due to large zero-point fluctuations of the H positions. In this case, the estimated magnetic model lies close to the classical tricritical point between ferromagnetic, zigzag and incommensurate spiral orders, what may contribute to the lack of magnetic ordering. However, we also find that substitution of H by D (deuterium) as well as disorder-induced inhomogeneities destabilize the O-H/D-O bonds modifying strongly the local magnetic couplings. These results suggest that the magnetic response in H$_3$LiIr$_2$O$_6$ is likely sensitive to both the stoichiometry and microstructure of the samples and emphasize the importance of a careful treatment of hydrogen for similar systems.