  The mechanism of unconventional superconductivity in correlated materials
remains a great challenge in condensed matter physics. The recent discovery of
superconductivity in infinite-layer nickelates, as analog to high-Tc cuprates,
has opened a new route to tackle this challenge. By growing 8 nm Pr0.8Sr0.2NiO2
films on the (LaAlO3)0.3(Sr2AlTaO6)0.7 substrate, we successfully raise the
transition temperature Tc from 9 K in the widely studied SrTiO3-substrated
nickelates into 15 K. By combining x-ray absorption spectroscopy with the
first-principles and many-body simulations, we find a positive correlation
between Tc and the pre-edge peak intensity, which can be attributed to the
hybridization between Ni and O orbitals induced by the strain. Our result
suggests that structural engineering can further enhance unconventional
superconductivity, and the charge-transfer property plays a crucial role in the
pairing strength.
