Pressure-induced dimerization and collapse of antiferromagnetism in the Kitaev material $\alpha$-Li$_2$IrO$_3$

TL;DR

This study investigates how hydrostatic pressure affects the magnetic and structural phases of the Kitaev material $ extalpha$-Li$_2$IrO$_3$, revealing pressure-induced dimerization and suppression of antiferromagnetism.

Contribution

It provides the first detailed phase diagram showing pressure-induced magnetic enhancement followed by a transition to a nonmagnetic dimerized phase in $ extalpha$-Li$_2$IrO$_3$.

Findings

Neel temperature slightly increases with pressure up to 1.2 GPa.

A first-order transition to a nonmagnetic dimerized phase occurs above 1.2 GPa.

The critical pressure for dimerization is temperature-dependent.

Abstract

We present magnetization measurements carried out on polycrystalline and single-crystalline samples of $\alpha$-Li$_2$IrO$_3$ under hydrostatic pressures up to 2 GPa and establish the temperature-pressure phase diagram of this material. The N\'eel temperature ($T_{\rm{N}}$) of $\alpha$-Li$_2$IrO$_3$ is slightly enhanced upon compression with $dT_{\rm{N}}/dp$ = 1.5 K/GPa. Above 1.2 GPa, $\alpha$-Li$_2$IrO$_3$ undergoes a first-order phase transition toward a nonmagnetic dimerized phase, with no traces of the magnetic phase observed above 1.8 GPa at low temperatures. The critical pressure of the structural dimerization is strongly temperature-dependent. This temperature dependence is well reproduced on the ab initio level by taking into account lower phonon entropy in the nonmagnetic phase. We further show that the initial increase in $T_{\rm{N}}$ of the magnetic phase is due to a weakening of the Kitaev interaction $K$ along with the enhancement of the Heisenberg term $J$ and off-diagonal anisotropy $\Gamma$. Our study reveals a common thread in the interplay of magnetism and dimerization in pressured Kitaev materials.