We perform Raman spectroscopy studies on α-RuCl3 at room temperature to explore its phase transitions of magnetism and chemical bonding under pressures. The Raman measurements resolve two critical pressures, about p1=1.1~GPa and p2=1.7~GPa, involving very different intertwining behaviors between the structural and magnetic excitations. With increasing pressures, a stacking order phase transition of α-RuCl3 layers develops at p1=1.1~GPa, indicated by the new Raman phonon modes and the modest Raman magnetic susceptibility adjustment. The abnormal softening and splitting of the Ru in-plane Raman mode provide direct evidence of the in-plane dimerization of the Ru-Ru bonds at p2=1.7~GPa. The Raman susceptibility is greatly enhanced with pressure increasing and sharply suppressed after the dimerization. We propose that the system undergoes Mott collapse at p2=1.7~GPa and turns into a dimerized correlated band insulator. Our studies demonstrate competitions between Kitaev physics, magnetism, and chemical bondings in Kitaev compounds.
@article{arxiv.1807.08211,
title = {Raman evidence for dimerization and Mott collapse in $\alpha$-RuCl$_3$ under pressures},
author = {Gaomin Li and Xiaobin Chen and Yuan Gan and Fenglei Li and Mingqi Yan and Shenghai Pei and Yujun Zhang and Le Wang and Huimin Su and Junfeng Dai and Yuanzhen Chen and Youguo Shi and XinWei Wang and Liyuan Zhang and Shanmin Wang and Dapeng Yu and Fei Ye and Jia-Wei Mei and Mingyuan Huang},
journal= {arXiv preprint arXiv:1807.08211},
year = {2019}
}