Tunneling spectra with gaplike features observed in nickelate La3Ni2O7 at ambient pressure

The recent discovery of high-Tc superconductivity near 80 K in the bilayer nickelate La3Ni2O7 has attracted widespread attention. The prerequisite to understanding the unconventional superconductivity in La3Ni2O7 is the determination of the electronic properties, such as the band structure and possible correlation effect. Here, we report a set of data on single-particle tunneling measurements on La3Ni2O7 single crystals at ambient pressure. A gaplike feature was observed in the tunneling spectra at low energies around the Fermi energy. The spectrum looks roughly symmetric with gap edges at about +98 and -92 meV. We attribute this gaplike feature to two alternative origins: either reflecting the bonding and antibonding bands derived from the Ni-3dz2 orbital, or a mixed contribution from a density wave gap and these two bands. Meanwhile, a finite density of states remains even in the gapped region, which is thought to be the vestige contribution of the Ni-3dx2-y2 orbital. Furthermore, it is found that the density of states is suppressed in a wide energy range with a sharp rise at about +/- 1.4 eV, indicating a general correlation effect. Theoretical calculations give partial consistency with the experimental observations. Our results provide important information to understand the electronic states of La3Ni2O7 at ambient pressure.