Mott-Hubbard quantum criticality in paramagnetic CMR pyrochlores

We present a correlated ab initio description of the paramagnetic phase of ${\mathrm{Tl}}_{2}{\mathrm{Mn}}_{2}{\mathrm{O}}_{7}$, employing a combined local density approximation with multiorbital dynamical mean-field theory treatment. We show that the insulating state observed in this colossal magnetoresistance pyrochlore is determined by strong Mn intra- and inter-orbital local electron-electron interactions. Hybridization effects are reinforced by the correlation-induced spectral weight transfer. Our result coincides with optical conductivity measurements, whose low-energy features are well accounted for by our theory. We also study the disorder-driven insulator-metal transition of doped compounds, showing the proximity of ${\mathrm{Tl}}_{2}{\mathrm{Mn}}_{2}{\mathrm{O}}_{7}$ to quantum phase transitions, in agreement with recent measurements.