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.
Highlights
inverse photoemission (IPE) spectra and was found to be 1.9 eV, much larger than previously estimated values
An angle-resolved photoemission spectroscopy (ARPES) study showed that the Fermi level EF is located 1.2 eV above the valence band maximum, suggesting that the band gap should be larger than 1.2 eV18
We overlaid the band dispersions based on the results of Local density approximation (LDA) +spin-orbit coupling (SOC) +U calculations; the result is shown in the right-hand side of Fig. 1(d)
Summary
IPE spectra and was found to be 1.9 eV, much larger than previously estimated values. The honeycomb Kitaev model has attracted significant attention as a feasible model for a quantum-spin-liquid ground state[1,2,3,4,5] In this model, a strong spin-orbit coupling (SOC) plays a critical role because it provides a bond-direction-dependent exchange interaction that results in spin frustration. Local density approximation (LDA) calculations reveal that the interplay between SOC and electron correlation plays an important role in determining the insulating ground state of α-RuCl3. Some features of the PE and IPE spectra could not be fully explained by the band calculations, implying a strongly correlated ground state To explain such detailed features, we performed configuration-interaction (CI) calculations for a RuCl63− cluster and determined the microscopic parameters relevant to Kitaev physics
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