Pyrochlore Oxide Hg2Os2O7 on Verge of Metal-Insulator Boundary

TL;DR

This study investigates Hg2Os2O7, a pyrochlore oxide near the metal-insulator boundary, revealing its likely semimetallic AIAO magnetic order and its potential for exploring 5d electron instabilities.

Contribution

The paper provides the first detailed thermodynamic, muSR, and neutron diffraction analysis of Hg2Os2O7, showing its proximity to the metal-insulator transition and its semimetallic AIAO state.

Findings

Hg2Os2O7 exhibits a magnetic transition around 88 K with AIAO order.

Resistivity measurements indicate metallic behavior down to 2 K.

Hg2Os2O7 is on the verge of the metal-insulator boundary, serving as a platform for studying 5d electron correlations.

Abstract

Semimetallic osmium pyrochlore oxide Cd2Os2O7 undergoes a magnetic transition to an all-in-all-out (AIAO)-type order at 227 K, followed by a crossover to an AIAO insulator at around 210 K. Here, we studied the isostructural and isoelectronic compound Hg2Os2O7 through thermodynamic measurements, muSR spectroscopy and neutron diffraction experiments. A similar magnetic transition, probably to an AIAO-type order, was observed at 88 K, while the resistivity showed a decrease at the transition and remained metallic down to 2 K. Thus, the ground state of Hg2Os2O7 is most likely an AIAO semimetal, which is analogous to the intermediate-temperature state of Cd2Os2O7. Hg2Os2O7 exists on the verge of the metal-insulator boundary on the metal side and provides an excellent platform for studying the electronic instability of 5d electrons with moderate electron correlations and strong spin-orbit interactions.