  Although Sr3Ru2O7 has not been reported to exhibit superconductivity so far,
ac susceptibility measurements revealed multiple superconducting transitions
occurring in the Sr3Ru2O7 region cut from Sr3Ru2O7-Sr2RuO4 eutectic crystals.
Based on various experimental results, some of us proposed the scenario in
which Sr2RuO4 thin slabs with a few layers of the RuO2 plane are embedded in
the Sr3Ru2O7 region as stacking faults and multiple superconducting transitions
arise from the distribution of the slab thickness. To examine this scenario, we
measured the resistivity along the ab plane (rho_ab) using a Sr3Ru2O7-region
sample cut from the eutectic crystal, as well as along the c axis (rho_c) using
the same crystal. As a result, we detected resistance drops associated with
superconductivity only in rho_ab, but not in rho_c. These results support the
Sr2RuO4 thin-slab scenario. In addition, we measured the resistivity of a
single crystal of pure Sr3Ru2O7 with very high quality and found that pure
Sr3Ru2O7 does not exhibit superconductivity down to 15 mK.
