Electronic correlation effects and orbital density wave in the layered compound 1T-TaS2

In this paper, we present the electronic structures and orbital-resolved electronic properties of structurally distorted 1T - TaS2 bulk and monolayer within density functional theory approaches. The relaxed commensurate-charge-density-wave (CCDW) structure shows that 13 Ta atoms condense into a star-of-David cluster, accompanied by a buckling of neighboring S planes. Through detailed analyses to the orbital characters near the Fermi level, we show that there exists an orbital-density-wave (ODW) order, which is predominantly contributed by Ta-5d(3z2-r2) orbital in the central Ta of the star-of-David cluster. We further demonstrate that the structural distortion, together with the Coulomb interaction, stabilizes the CCDW insulating ground state with an ODW order. The results obtained from dynamical mean-field theory confirm the role of the electronic correlation. Moreover, such an ODW ground state favors an intralayer ferromagnetic order in bulk and monolayer 1T - TaS2, and an interlayer antiferromagnetic order in bulk. We propose that 1T - TaS2 monolayer may pave new ways to study exciton physics, flat-band physics, and potential applications in luminescence.