Disentangling real space fluctuations: the diagnostics of metal-insulator transitions beyond single-particle spectral functions

The destruction of metallicity due to the mutual Coulomb interaction of quasiparticles gives rise to fascinating phenomena of solid state physics such as the Mott metal-insulator transition and the pseudogap. A key observable characterizing their occurrences is the single-particle spectral function, determined by the fermionic self-energy. In this paper we investigate in detail how real space fluctuations are responsible for a self-energy that drives the Mott-Hubbard metal-insulator transition. To this aim we first introduce a real space fluctuation diagnostics approach to the Hedin equation, which connects the fermion-boson coupling vertex $λ$ to the self-energy $Σ$. Second, by using cellular dynamical mean-field theory calculations for $λ$ we identify the leading physical processes responsible for the destruction of metallicity across the transition.