Emergence of a diffusive metal state with no magnetic order near the Mott transition in frustrated pyrochlore-type molybdates.

The electron-correlation driven metal-insulator (Mott) transition in pyrocholore-type R 2 Mo 2 O 7 (R 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.