ARPES study of the Kitaev Candidate $\alpha$-RuCl$_3$

TL;DR

This study uses ARPES measurements and theoretical calculations to investigate the electronic structure of $ extalpha$-RuCl$_3$, revealing a persistent Mott gap and complex doping effects indicative of strong spin fluctuations near a potential Kitaev spin liquid state.

Contribution

It combines ARPES experiments with advanced calculations to elucidate the electronic and magnetic properties of $ extalpha$-RuCl$_3$, highlighting its Mott insulating nature and doping-induced spectral changes.

Findings

Large Mott gap persists above magnetic ordering temperature

Spectral weight transfer occurs with electron doping

Strong spin fluctuations influence the electronic evolution

Abstract

$\alpha$-RuCl$_3$ has been hinted as a spin-orbital-assisted Mott insulator in proximity to a Kitaev spin liquid state. Here we present ARPES measurements on single crystal $\alpha$-RuCl$_3$ in both the pristine and electron-doped states, and combine them with LDA+SOC+U calculations performed for the several low-energy competing magnetically ordered states as well as the paramagnetic state. A large Mott gap is found in the measured band structure of the pristine compound that persists to more than 20 times beyond the magnetic ordering temperature, though the paramagnetic calculation shows almost no gap. Upon electron doping, spectral weight is transferred into the gap but the new states still maintain a sizable gap from the Fermi edge. These findings are most consistent with a Mott insulator with a somewhat exotic evolution out of the Mott state with both temperature and doping, likely related to unusually strong spin fluctuations.