Electronic crossover in the highly anisotropic normal state of Sr2RuO4 from pressure effects on electrical resistivity

We investigated pressure dependence of the electrical resistivity of the only copper-free layered-perovskite superconductor Sr2RuO4. The characteristic temperature TM, where the out-of-plane resistivity pc changes from metallic behavior to nonmetallic behavior with increasing temperature, increases with hydrostatic pressure. In contrast, the absolute value of pc at TM is almost independent of pressure. Such a change over in pc is ascribable to the crossover from the diffusion process of quasiparticles between the adjacent layers to the thermally assisted hopping process. The pressure effects on pc are possibly characterized by the enhanced transfer integral along the c axis by pressure. On the other hand, in the temperature dependence of the in-plane resistivity, we observed an intriguing hump that appears at low T less than TM in the pressure range from 1.5 to 5 GPa, and vanishes on applying higher pressure. This behavior may be comprehensible from the view of the two-dimensional ferromagnetic spin fluctuations enhanced by pressure