Speaker
Description
Tharathep Plienbumrung,1,2 Maria Daghofer,1,2 Michael Schmid,3 and Andrzej M. Oleś 4,5
1 Institute for Functional Matter and Quantum Technologies, University of Stuttgart, D-70550 Stuttgart, Germany
2 Center for Integrated Quantum Science and Technology, University of Stuttgart, D-70550 Stuttgart, Germany
3 Waseda Research Institute for Science and Engineering, Waseda University, Shinjuku, Tokyo 169-8555, Japan
4 Max Planck Institute for Solid State Research, D-70569 Stuttgart, Germany
5 Institute of Theoretical Physics, Jagiellonian University, PL-30348 Kraków, Poland
Superconductivity found in doped NdNiO2 is puzzling as two local symmetries of doped NiO2 layers compete, with presumably far-reaching implications for the involved superconductivity mechanism. With increasing value of the charge-transfer energy we observe upon hole doping the expected crossover from the cuprate regime dominated by Zhang-Rice singlets to the local triplet regime for doped nickelates. A second Ni(3d) orbital can easily become relevant, with either the xy or the 3z2−r2 orbitals contributing together with the x2−y2 orbital to the formation of local triplet states. The phase transition to triplet states depends on the interorbital Coulomb repulsion Udp (acting between Ni and O) favors on-site triplets implies that correlation effects beyond purely on-site interactions should be taken into account when obtaining effective two-band models. With increasing value of the charge-transfer energy, we observe the expected crossover from a singlet to a local triplet regime upon hole doping. The screened interactions for the s band suggest the importance of rare-earth atoms in superconducting nickelates.
Next, starting from an effective two-dimensional two-band model for infinite-layer nickelates, consisting of bands obtained from d- and s-like orbitals, we investigate to which extent it can be mapped onto a single-band Hubbard model. We identify screening of the more itinerant s-like band as an important driver [2]. In the absence of screening one strongly correlated band gives an antiferromagnetic ground state. For weak screening, the strong correlations push electrons out of the s band so that the undoped nickelate remains a Mott insulator with a single half-filled x2-y2 band and two Hubbard sub-bands [3]. This regime differs markedly from the observations in high-Tc cuprates---then pairing with s-wave symmetry would rather be expected in the superconducting state. In contrast, for strong screening, the s and x2−y2 bands are both partly filled and couple only weakly, so that one approximately finds a self-doped d band, as well as tendencies toward d-wave pairing. Particularly, in the regime of strong screening mapping to a one-band model gives significant spectral weight transfers when a second s band is also partly filled. We thus find that both one-band physics and a Kondo-lattice-like regime emerge from the same two-orbital model, depending on the strength of electronic correlations and on the size of the s-band pocket.
[1] T. Plienbumrung, M. Daghofer, and A.M. Oleś, Phys. Rev. B 103, 104513 (2021).
[2] T. Plienbumrung, M. Daghofer, M. Schmid, and A.M. Oleś, Phys. Rev. B 106, 134504 (2022).
[3] T. Plienbumrung, M. Daghofer, M. Schmid, and A.M. Oleś, Acta Phys. Pol. A 143, 200 (2023).
