  While the superconducting transition temperature Tc of Sr2RuO4 is 1.5 K, its
onset Tc is enhanced as high as 3 K in the Sr2RuO4-Ru eutectic system, which is
often referred to as the 3-K phase. We have investigated effects of uniaxial
pressure on the non-bulk superconductivity in the 3-K phase. While Tc of pure
Sr2RuO4 is known to be suppressed by hydrostatic pressure, a large enhancement
of the superconducting volume fraction of the 3-K phase was observed for both
out-of-plane and in-plane uniaxial pressures. Especially, under the in-plane
pressure, the shielding fraction at 1.8 K of only less than 0.5% at 0 GPa
exceeds 40% at 0.4 GPa. Such a large shielding fraction suggests that under the
uniaxial pressure interfacial 3-K phase superconductivity penetrates deep into
the bulk of Sr2RuO4. The present finding provides a significant implication to
the unresolved origin of the enhancement of Tc to 3 K in the Sr2RuO4-Ru
eutectic system.
