Effective bandstructure in the insulating phase versus strong dynamical correlations in metallic VO2

Using a general analytical continuation scheme for cluster dynamical mean-field calculations, we analyze real-frequency self-energies, momentum-resolved spectral functions, and one-particle excitations of the metallic and insulating phases of VO2. While for the former dynamical correlations and lifetime effects prevent a description in terms of quasiparticles, the excitations of the latter allow for an effective bandstructure. We construct an orbital dependent, but static one-particle potential that reproduces the essentials of the full many-body spectrum. Yet, the ground state is well beyond a static one-particle description. The emerging picture gives a nontrivial answer to the decade-old question of the nature of the insulator, which we characterize as a "many-body Peierls" state, stressing the joint effect of lattice symmetry breaking and Coulomb correlations.