  Iridium-based 5d transition-metal oxides are attractive candidates for the
study of correlated electronic states due to the interplay of enhanced
crystal-field, Coulomb and spin-orbit interaction energies. At ambient
pressure, these conditions promote a novel Jeff = 1/2 Mott insulating state,
characterized by a gap of the order of ~0.1 eV. We present high-pressure
electrical resistivity measurements of single crystals of Sr2IrO4 and Sr3Ir2O7.
While no indications of a pressure-induced metallic state up to 55 GPa were
found in Sr2IrO4, a strong decrease of the gap energy and of the resistance of
Sr3Ir2O7 between ambient pressure and 104 GPa confirm that this compound is in
the proximity of a metal-insulator transition.
