Pressure-Induced Transition from a Correlated Insulator to a Fermi Liquid Observed in Geometrically Frustrated Hg₂Ru₂O₇ Pyrochlore

Abstract

Recently discovered pyrochlore oxide, Hg₂Ru₂O₇, shows a first order metal–insulator transition at T∼107 K. The effect of hydrostatic pressure on the M–I transition was studied by measuring the temperature dependent resistivity ρ(T) up to 12 GPa. The application of pressure suppressed the low temperature insulating state and eventually induced a transition from a correlated insulator to a metal at around 5 GPa. With decreasing temperature, ρ(T) in the metallic phase showed a rapid decrease at around T^*∼40 K, likely representing the onset of a coherent–incoherent crossover, and eventually a well defined T²-dependence at low temperatures, indicative of the presence of coherent quasi-particles. All these results point the formation of a Fermi liquid with an enhanced mass in the metallic state of this geometrically frustrated system, located close proximity to the correlation driven metal–insulator transition.