Spectroscopic Imaging Scanning Tunneling Microscopy (SI-STM) of La₃Ni₂O₇

The discovery of bulk superconductivity with critical temperature (T_c) above liquid nitrogen temperature (77 K) in cuprates led to a paradigm shift in the mechanisms underlying superconductivity. While the exact mechanism remains unknown, it is distinct from the electron-phonon picture in BCS theory¹. Nickel-oxide compounds, or nickelates, have long been sought after due to their structural similarities to cuprate superconductors². Recent experiments show clear evidence for superconductivity above 80 K in La₃Ni₂O₇ under high pressure (> 14 GPa) and signs of density wave order below 150 K³. In this talk, we present the first Spectroscopic Imagining Scanning Tunneling Microscopy (SI-STM) results on La₃Ni₂O₇ showing an unambiguous gap-like feature with a gap size of ~ 11 meV. The gap-like feature is attributed to a spin density wave (SDW) consistent with previously reported results. Moreover, we will discuss quasiparticle interference (QPI) data that suggests that the SDW induces a reconstruction of the La₃Ni₂O₇ band structure. Finally, we compare the results obtained from SI-STM to theory in order to further understand the normal-state electronic structure in La₃Ni₂O₇.

References

[1] Bednorz, J. G. & Müller, K. A. Possible highT_c superconductivity in the Ba–La–Cu–O system. Z. Phys. B Condens. Matter 64, 189–193 (1986).

[2] Hayward, M. A., Green, M. A., Rosseinsky, M. J. & Sloan, J. Sodium hydride as a powerful reducing agent for topotactic oxide deintercalation: synthesis and characterization of the nickel(I) oxide LaNiO₂. J. Am. Chem. Soc. 121, 8843–8854 (1999).

[3] Sun, H., Huo, M., Hu, X. et al. Signatures of superconductivity near 80 K in a nickelate under high pressure. Nature 621, 493–498 (2023)