Revelation of Mott insulating state in layered honeycomb lattice Li2RuO3.

We investigate the role of electron correlation in the electronic structure of honeycomb lattice Li2RuO3using photoemission spectroscopy and band structure calculations. Monoclinic Li2RuO3having Ru network as honeycomb lattice undergoes magneto-structural transition atTc∼ 540 K from high temperature phaseC2/mto low temperature dimerized phaseP21/m. Room temperature valence band photoemission spectra reveal an insulating ground state with no intensity at Fermi level (EF). Ru 4dband extracted from high and low photon energy valence band photoemission spectra reveal that the surface and bulk electronic structures are very similar in this system. Band structure calculations using generalized gradient approximation leads to metallic ground state while screened hybrid (YS-PBE0) functional reveals opening up of a gap in almost degeneratedzx/dyzorbitals, whereasdxyorbital is already gapped. Ru 3dcore level spectra with prominent unscreened feature provides direct evidence of strong electron correlation among Ru 4delectrons which is also manifested by |E-EF|2dependence of spectral density of states in the vicinity ofEFin the high-resolution spectra, establishing Li2RuO3as Mott insulator.