Topotactic Hydrogen in Nickelate Superconductors and Akin Infinite-Layer Oxides ABO2

Abstract

Superconducting nickelates appear to be difficult to synthesize. Since the chemical reduction of ABO3 (A: rare earth; B transition metal) with CaH2 may result in both, ABO2 and ABO2H, we calculate the topotactic H binding energy by density functional theory (DFT). We find intercalating H to be energetically favorable for LaNiO2 but not for Sr-doped NdNiO2. This has dramatic consequences for the electronic structure as determined by DFT+dynamical mean field theory: that of 3d 9 LaNiO2 is similar to (doped) cuprates, 3d 8 LaNiO2H is a two-orbital Mott insulator. Topotactic H might hence explain why some nickelates are superconducting and others are not.

Nickelate superconductors—a renaissance of the one-band Hubbard model

“…It leaves us with a well defined window with just five Nd-5d and five Ni-3d around the Fermi energy. For these remaining ten orbitals we do a Wannier function projection (see Supplementary Note 2) and subsequent DMFT calculation with constrained random phase approximation (cRPA) calculated inter-orbital interaction U 0 ¼ 3:10eV (2.00 eV) and Hund's exchange J = 0.65 eV (0.25 eV) for Ni (Nd) 28 . Figure 2 presents the calculated DMFT spectral function for these ten bands.…”

“…At larger doping and when including the Nd-interaction in DMFT the Γ-pocket is shifted above E F , see Fig. 2 below and e.g., refs 16,25,28,32 . Figure 1b further shows the superconducting critical temperature T C of the thus derived and doped Hubbard model, calculated by a method that is appropriate in the strong coupling regime: the dynamical vertex approximation (DΓA 37 ).…”

“…Addressing these points calls for a proper treatment of electronic correlations since e.g., the formation of Hubbard side bands has the potential to alter the orbitals that host the holes induced by Sr doping. In a material-specific, ab initio way this can be done using DFT + dynamical mean-field theory (DMFT) 36 and several groups have done such DFT + DMFT studies 25,26,28,33,34 . Most of these focus on the undoped parent compound and arrive at a picture that the main players are the Ni d x 2 Ày 2 orbital plus A (and Γ) pocket.…”

Multiorbital Processes Rule the Nd1−xSrxNiO2Lechermann1 2020Phys. Rev. X10510880View full textAdd to dashboardCite

“…An experimentally found [1] resistivity upturn below about T ∼ 70 K might indeed be indicative of related processes. The third, highly debated question is most relevant for the superconducting mechanism, and it deals with the issue of deciding lowenergy physics based on single-Ni-orbital processes of the Ni-d x 2 −y 2 kind [18][19][20][21][22][23] versus processes of the multi-Niorbital kind [7,[9][10][11]31] at stoichiometry and with finite hole doping from replacing Nd by Sr.…”

Magnetic exchange coupling in cuprate-analog d9 nickelates

“…However, it should be noted that the origin of small J in NdNiO 2 may be ascribed to another notable difference from the cuprates, namely, NdNiO 2 is not a Mott insulator due to the self-doping effect. In NdNiO 2 , orbitals in the Nd layer form extra Fermi pockets on top of the large Fermi surface formed by the Ni 3d x 2 −y 2 orbital and the Ni 3d x 2 −y 2 orbital is hole doped, i.e., the filling of the Ni 3d orbitals deviates from d 9 [14,15,19,33,49,56]. The self-doping naturally explains the absence of Mott insulating behavior in NdNiO 2 .…”