Emergence of a Diffusive Metal State with No Magnetic Order near the Mott Transition in Frustrated Pyrochlore-Type Molybdates

摘要

The electron-correlation driven metal-insulator (Mott) transition in pyrocholore-type R_2Mo_2O_7(N being rare-earth-metal ions) is accompanied by the change of the magnetic state from ferromagnetic to spin glass due to the competing double-exchange and superexchange interactions on the frustrated lattice. By application of high pressures on the compounds with Mott criticality, however, a new unique paramagnetic metal phase is observed to show up with nearly temperature-independent high resistivity close to the Ioffe-Regel limit. A possible non-Fermi-liquid character of this anomalously diffuse metallic state is argued in terms of the extended double-exchange model with the magnetically frustrated local S = 1/2 spins.