Single-crystal x-ray diffraction studies with synchrotron radiation on the honeycomb iridate α-Li2IrO3 reveal a pressure-induced structural phase transition with symmetry lowering from monoclinic to triclinic at a critical pressure of Pc = 3.8 GPa. According to the evolution of the lattice parameters with pressure, the transition mainly affects the ab plane and thereby the Ir hexagon network, leading to the formation of Ir--Ir dimers. These observations are independently predicted and corroborated by our \textit{ab initio} density functional theory calculations where we find that the appearance of Ir--Ir dimers at finite pressure is a consequence of a subtle interplay between magnetism, correlation, spin-orbit coupling, and covalent bonding. Our results further suggest that at Pc the system undergoes a magnetic collapse. Finally we provide a general picture of competing interactions for the honeycomb lattices A2MO3 with A= Li, Na and M = Ir, Ru.
@article{arxiv.1712.01669,
title = {Competition between spin-orbit coupling, magnetism, and dimerization in the honeycomb iridates: $\alpha$-Li$_{2}$IrO$_{3}$ under pressure},
author = {V. Hermann and M. Altmeyer and J. Ebad-Allah and F. Freund and A. Jesche and A. A. Tsirlin and M. Hanfland and P. Gegenwart and I. I. Mazin and D. I. Khomskii and R. Valentí and C. A. Kuntscher},
journal= {arXiv preprint arXiv:1712.01669},
year = {2018}
}