Anisotropic uniaxial pressure response of the Mott insulator Ca2RuO4

We have investigated the in-plane uniaxial pressure effect on the antiferromagnetic Mott insulator Ca${}_{2}$RuO${}_{4}$ from resistivity and magnetization measurements. We succeeded in inducing the ferromagnetic metallic phase at lower critical pressure than by hydrostatic pressure, indicating that the flattening distortion of the RuO${}_{6}$ octahedra is more easily released under in-plane uniaxial pressure. We also found a striking in-plane anisotropy in the pressure responses of various magnetic phases: although the magnetization increases monotonically with pressure diagonal to the orthorhombic principal axes, the magnetization exhibits peculiar dependence on pressure along the in-plane orthorhombic principal axes. This peculiar dependence can be explained by a qualitative difference between the uniaxial pressure effects along the orthorhombic $a$ and $b$ axes, as well as by the presence of twin domain structures.