Colossal magnetoresistance accompanying a structural transition in a highly two-dimensional metallic state of Ca3Ru2O7 -: art. no. 104414

We report the high-field magnetoresistivity, magnetization, and magnetostriction data of a bilayered ruthenate Ca3Ru2O7 grown by a floating-zone method. The samples used in this study show metallic inplane conduction, but nonmetallic interplane conduction, below 30 K; these results are suggestive of a highly two-dimensional metallic ground state. We demonstrate here the existence of two types of field-induced metamagnetic transitions at 6 and 15 T, accompanied by the colossal magnetoresistance effect in the interplane conduction [rho(c)(20 T)/rho(c)(0 T)<10(-3)]. Interestingly, the higher-field transition is accompanied by large inplane lattice shrinkage that is sufficient to cause orbital polarization in nearly threefold t(2g) orbitals. The lattice change due to the magnetic field coincides with the discontinuity at 48 K observed in the thermal contraction data, suggesting that the high-temperature crystal structure is restored by the application of a magnetic field. In this paper, we will discuss this anomalous coupling between spin, charge, and lattice in Ca3Ru2O7 in terms of structural distortions.