Progress of ambient-pressure superconductivity in bilayer nickelate thin films

This review summarizes recent progress of ambient-pressure superconductivity in bilayer nickelate La$_3$Ni$_2$O$_7$ thin films, a major advancement following the discovery of high-pressure superconductivity in bulk La$_3$Ni$_2$O$_7$. First, we explain how epitaxial strain engineering enables ambient-pressure superconductivity in La$_3$Ni$_2$O$_7$ thin films, with compressive strain from substrates like SrLaAlO$_4$ stabilizing superconductivity. Next, we review experimental characterizations of related systems, with particular emphasis on ARPES measurements that have shown conflicting Fermi surface topologies. We then discuss progress in increasing the superconducting transition temperature $T_c$. Finally, we summarize theoretical studies of the electronic structure and pairing symmetry of La$_3$Ni$_2$O$_7$ thin films. Together, these advances establish bilayer nickelate thin films as a highly tunable and promising platform for exploring high-$T_c$ superconductivity.