under high pressure: theory vs. experiment*

Recent discovery of high Tc superconductivity in a bilayer nickelate La3Ni2O7 has sparked a vast wave of new interest [1]. In fact, this very material was previously proposed as a good starting point for seeking high Tc superconductivity by one of the present authors [2].  Discussed there was the possibility of realizing a nearly half-filled bilayer Hubbard model with large interlayer hopping utilizing the d3z2-r2 orbitals. In the present study, we construct a four-orbital (d3z2-r2 +dx2-y2, x 2) model of La3Ni2O7 under high pressure through DFT calculations and Wannierization, and apply FLEX to study   superconductivity [3]. We find that the Tc can be comparable to those of the high Tc  cuprates, and the effects of the dx2-y2 orbitals are limited, so that the experimental Tc ~ 80K can be understood as a consequence of realizing the bilayer Hubbard model comprising the d3z2-r2 orbitals. We next study the possibility of superconductivity in a trilayer nickelate La4Ni3O10 [4]. We perform structural optimization calculations at high pressures, which results in tetragonal symmetry of the lattice. Using the obtained structure, the possibility of superconductivity is studied using FLEX, which shows that superconductivity with Tc comparable to that of relatively low Tc cuprates is possible. These results are compared with experiments.

[1] H. Sun et al., Nature 621, 493 (2023). [2] M. Nakata et al., Phys. Rev. B 95, 214509 (2017). [3] H. Sakakibara et al., arXiv: 2306.06039.  [4] H. Sakakibara et al., arXiv: 2309.09462.