  Recently, the signatures of superconductivity near 80 K have been discovered
in the single crystal of La3Ni2O7 under pressure and thus has attracted
significant attention. However, there are several critical issues that have
been perplexing the scientific community. These include (1) what factors
contribute to the poor reproducibility of the experimental results, (2) what
the intrinsic nature of the pressure-induced superconductivity is, bulk or
filamentary, (3) where the superconducting phase locates within the sample if
it is indeed filamentary, and (4) what the oxygen content is necessary for the
development and stabilization of superconductivity. In this study, we employ
comprehensive high-pressure measurements to address these crucial issues. By
demonstrating both zero resistance and diamagnetism, we are the first to
confirm the existence of high-temperature superconductivity in La3Ni2O7.
Through our sensitive ac susceptibility measurements, we are the first to
quantify the superconducting volume fraction in La3Ni2O7 at the level of 1%. In
tandem with our observation of the anisotropic zero-resistance state only in
some of the samples, we suggest that the superconductivity in this nickelate is
filamentary-like. By our scanning transmission electron microscopy (STEM)
investigations, we propose that the filamentary superconductivity most likely
emerges at the interface between the La3Ni2O7 and La4Ni3O10 phases. Further,
the upper and lower bounds of the oxygen content required for the presence of
superconductivity were determined. Our results provide not only new insights
into understanding the puzzling issues in this material, but also significant
information for achieving a better understanding on the superconductivity of
this material.
