High-energy spin excitations in a bilayer nickelate high-Tc superconductor

The quest for new high-temperature superconductors has attracted intense research efforts over the years. Recently, the bilayer nickelate La3Ni2O7 emerges as a potential new high-Tc superconductor. It features a bilayer NiO2 square structure with active 3d_{x^2-y^2} and 3d_{z^2} orbitals, with 1/4 and 1/2 filling fractions respectively. The p-orbital of apical oxygen connecting adjacent NiO2 layers couples the two nearest-neighbors 3d_{z^2} orbitals and mediates a super-exchange interaction between them, which is antiferromagnetic (AFM). Density functional theory calculations and several theoretical models suggest the important role this interaction played in the superconducting pairing mechanism. Hence, the verification of this theoretical framework is of paramount importance in unraveling the underlying superconducting mechanism. Given the presence of AFM interlayer coupling and half-filling of 3d_{z^2} orbitals, a Mott localized phase is anticipated with rung singlet formed at every site. Importantly, if this scenario is indeed correct, such singlet couplings should manifest even under ambient pressure, as the pressure required to induce superconductivity is relatively modest. Therefore, we proposal to measure the high-energy spin excitations of La3Ni2O7, with the objective of detecting potential excitations arising from the formation of spin singlets by 3d_{z^2} electrons.