Anisotropic giant magnetoresistance near the Mott transition in pressurized Ca2RuO4

We have observed an anisotropic and giant magnetoresistance (MR) in the 4d-electron Mott transition system of Ca2RuO4. On the border of the Mott transition (similar to 2 GPa), the MR effect at similar to 10 T reaches similar to-55% at T-C for longitudinal and similar to+120% at low temperatures for the transverse effects. The negative MR is most likely interpreted as a reduction in a ferromagnetic (FM) fluctuation at T-C. In contrast, the large positive effect is actually rare and is characteristic of the mixed state where the FM metallic islands are flecked with the insulating phases. We discuss the reason of the peculiar MR from the viewpoint of the anisotropic magnetism, the tunnel MR, and the orbital physics..