Mott-Hubbard quantum criticality in paramagnetic CMR pyrochlores

TL;DR

This paper uses advanced ab initio methods to explain the insulating behavior and quantum criticality in paramagnetic Tl$_2$Mn$_2$O$_7$ pyrochlores, aligning well with experimental optical data.

Contribution

It provides a correlated ab initio description of the paramagnetic phase, highlighting the role of strong electron-electron interactions and hybridization effects in CMR pyrochlores.

Findings

Insulating state driven by strong Mn electron interactions

Spectral weight transfer due to correlations matches optical data

Proximity to quantum phase transitions in doped compounds

Abstract

We present a correlated {\it ab initio} description of the paramagnetic phase of Tl$_2$Mn$_2$O$_7$, employing a combined local density approximation (LDA) with multiorbital dynamical mean field theory (DMFT) treatment. We show that the insulating state observed in this colossal magnetoresistance (CMR) 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 remarkably accounted for by our theory. Based on this agreement, we study the disorder-driven insulator-metal transition of doped compounds, showing the proximity of Tl$_2$Mn$_2$O$_7$ to quantum phase transitions, in agreement with recent measurements.