Pressure-induced transition from a correlated insulator to a fermi liquid observed in geometrically frustrated Hg ₂Ru ₂O ₇ pyrochlore

Recently discovered pyrochlore oxide, Hg ₂Ru ₂O ₇, 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 T ²-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.