Contrasting Pressure-Induced Metallization Processes in Layered Perovskites, α-Sr_{2}MO_{4} (M=V, Cr)

Electric resistivity, magnetic susceptibility, and x-ray diffraction measurements under high pressure are performed in both α-Sr_{2}VO_{4} and α-Sr_{2}CrO_{4}, which are carefully prepared with regard to their stoichiometry. These measurements reveal contrasting and peculiar metallization processes of these compounds with increasing pressure. In contrast to a previously reported one in a V compound, we find two kinds of pressure-induced metallic states at low- (T<50  K) and high-temperature (T>100  K) regions. The high-temperature one seems to emerge beyond the pressure-induced Mott transition. The low-temperature one might imply a topological nature of the V compound, which is expected in the spin-orbit coupled 3d^{1} state that arises from their degenerated d_{zx} and d_{yz} orbits.