Mott and pseudogap localization in pressurized NbO2

We present a detailed study of correlation-induced electronic reconstruction in baddeleyite-type ${\mathrm{NbO}}₂$, a distorted ${\mathrm{ZrO}}₂$-type structure that is found at pressures above 8.0 GPa. Based on density-functional plus dynamical mean-field theory (DFT$+$DMFT), we stress the importance of multiorbital Coulomb interactions in concert with first-principles band-structure calculations for a consistent understanding of emergent Mottness and pseudogap behavior in pressurized ${\mathrm{NbO}}₂$ and related ${d}¹$ systems. After a proper treatment of multiorbital electron-electron interactions, we find a nearly universal Mott behavior for the peak position of the lower Hubbard band that is independent of crystal- and band-structure details. We explain the nature of the metal-pseudogap-insulator transition to be seen in experiment, showing a first-order transition between two metallic states: a correlated metal and a pseudogap state with a deep density of states at the Fermi level. This emergent pseudogap phenomena is expected to play a central role toward quantum criticality in pressurized ${\mathrm{NbO}}₂$.