Pressure-induced metal-insulator transition of the mott insulator Ba₂IrO₄

The electrical resistivity of single crystals of the spin-orbit Mott insulator Ba₂IrO₄ has been measured at pressures up to 30 GPa and at temperatures from 100 mK to 300 K. Ba₂IrO₄ shows a metal-insulator transition at around P_c = 24 GPa, though it does not show superconductivity down to 100 mK. The low-temperature resistivity in the metallic state does not obey a conventional Fermi-liquid description. This suggests that carriers are incoherently scattered by antiferromagnetic quantum spin fluctuations. The critical exponent δ for the metal-insulator transition is about 1.6, indicating that Ba₂IrO₄ is located near the boundary between a Mott and an Anderson insulator. This means that even in a single crystal, the effect of crystallographic disorder should not be ignored.