Mott transition and anomalous resistive state in the pyrochlore molybdates

TL;DR

This paper develops a theoretical model for pyrochlore molybdates, explaining their phase transitions, resistivity anomalies, and orbital correlations through a Monte Carlo study of their minimal model.

Contribution

It provides a quantitative phase diagram and insights into the origin of resistivity anomalies and orbital correlations in pyrochlore molybdates, matching experimental observations.

Findings

Phase diagram closely matches experiments

Predicted unexplored orbital correlations

Explained anomalous resistivity origin

Abstract

The rare-earth based pyrochlore molybdates involve orbitally degenerate electrons Hund's coupled to local moments. The large Hund's coupling promotes ferromagnetism, the superexchange between the local moments prefers antiferromagnetism, and Hubbard repulsion tries to open a Mott gap. The phase competition is tuned by the rare-earth ionic radius, decreasing which leads to change from a ferromagnetic metal to a spin disordered highly resistive ground state, and ultimately an 'Anderson-Mott' insulator. We attempt a quantitative theory of the molybdates by studying their minimal model on a pyrochlore geometry, using a static auxiliary field based Monte Carlo. We establish a thermal phase diagram that closely corresponds to the experiments, predict the hitherto unexplored orbital correlations, quantify and explain the origin of the anomalous resistivity, and present dynamical properties across the metal-insulator transition.