Possible Fano effect and suppression of Andreev reflection in La$_3$Ni$_2$O$_7$

The recently-discovered high-temperature superconductor La$_3$Ni$_2$O$_7$ under high pressure has stimulated intensive debates. Key controversies concern interlayer versus intralayer pairing scenarios and if the hybridization plays a key role in establishing the superconductivity. But experimental clarification is difficult due to the limitation of employing state-of-the-art techniques under high pressure. Here we propose that quasiparticle tunneling and Andreev reflection may provide a feasible way to distinguish different pairing scenarios. We predict that an asymmetric Fano line shape may be induced by the hybridization between the $d_{x^2-y^2}$ metallic bands and the strongly renormalized flat $d_{z^2}$ quasiparticle bands. In the superconducting state, we show that the Andreev reflection should be greatly suppressed for interlayer pairing superconductivity with a small interlayer hopping. We propose future experiments to examine these predictions and help clarify the fundamental physics of superconducting La$_3$Ni$_2$O$_7$ and other multilayer nickelate superconductors.