  We report magnetic and inter-plane transport properties of Ca3Ru2O7 at high
magnetic fields and low temperatures. Ca3Ru2O7 with a bilayered orthorhombic
structure is a Mott-like system with a narrow charge gap of 0.1eV. Of a host of
unusual physical phenomena revealed in this study, a few are particularly
intriguing: (1) a collapse of the c-axis lattice parameter at a metal-nonmetal
transition, TMI (=48 K), and a rapid increase of TMI with low uniaxial pressure
applied along the c-axis; (2) quantum oscillations in the gapped, nonmetallic
state for 20 mK<T<6.5 K; (3) tunneling colossal magnetoresistance, which yields
a precipitate drop in resistivity by as much as three orders of magnitude; (4)
different in-plane anisotropies of the colossal magnetoresistance and
magnetization. All results appear to indicate a highly anisotropic ground state
and a critical role of coupling between lattice and magnetism. The implication
of these phenomena is discussed.
