Electronic Structure of the Kitaev Material α-RuCl3 Probed by Photoemission and Inverse Photoemission Spectroscopies

Abstract

Recently, α-RuCl3 has attracted much attention as a possible material to realize the honeycomb Kitaev model of a quantum-spin-liquid state. Although the magnetic properties of α-RuCl3 have been extensively studied, its electronic structure, which is strongly related to its Kitaev physics, is poorly understood. Here, the electronic structure of α-RuCl3 was investigated by photoemission (PE) and inverse-photoemission (IPE) spectroscopies. The band gap was directly measured from the PE and IPE spectra and was found to be 1.9 eV, much larger than previously estimated values. Local density approximation (LDA) calculations showed that the on-site Coulomb interaction U could open the band gap without spin-orbit coupling (SOC). However, the SOC should also be incorporated to reproduce the proper gap size, indicating that the interplay between U and SOC plays an essential role. Several features of the PE and IPE spectra could not be explained by the results of LDA calculations. To explain such discrepancies, we performed configuration-interaction calculations for a RuCl63− cluster. The experimental data and calculations demonstrated that the 4d compound α-RuCl3 is a Jeff = 1/2 Mott insulator rather than a quasimolecular-orbital insulator. Our study also provides important physical parameters required for verifying the proposed Kitaev physics in α-RuCl3.

Theoretical investigation of magnetic dynamics in α−RuCl3

“…Currently, considerable attention has been attracted to exotic physics driven by the interplay of the spinorbital coupling (SOC), crystal field and electronic correlation [1][2][3][4][5][6][7][8][9][10][11][12] . Especially, in 4d or 5d transition metal materials, neither the Hubbard interaction U nor the SOC λ can solely lead to the insulating behavior.…”

Vortex creation and control in the Kitaev spin liquid by local bond modulations

“…53 and 54. In the expansion, we set the onsite Coulomb interaction U , the Hund's-rule coupling J H /U , and the spin-orbit coupling coefficient λ to 5 eV, 0.1 eV, and 0.1 eV, respectively; the parameters are taken, in consideration of the theoretical and experimental studies for Ru metal [65], Sr 2 RuO 4 [66], and α-RuCl 3 [67,68].…”

Light-Induced Control of Magnetic Phases in Kitaev Quantum Magnets

“…Here, p † i σ denote ligand creation operators, with i , j the two ligands at the corners of neighboring edge-sharing octahedra that encase TM sites i, j. Throughout this study the values of these constants used were adapted from recent ab initio and photoemission studies: U = 3.0, J H = 0.45, U = U − 2J H , λ = 0.15, ∆ = 5, t 1 = 0.03, t 2 = 0.03, t 3 = −0.06, t 4 = −0.02 and t pd = −0.9 [37,38].…”