Electronic structure, orbital-dependent renormalizations, and magnetic correlations in double-layer La$_3$Ni$_2$O$_7$ under doping tuning

TL;DR

The study investigates how strong electronic correlations and chemical doping tune the normal-state electronic structure and magnetic correlations in the high-pressure double-layer nickelate $La_3Ni_2O_7$ using a fully self-consistent DFT+DMFT framework. It reveals pronounced orbital-selective mass renormalizations, incoherent Ni $3d$ spectral weights, and Lifshitz-like reconstructions of the Fermi surface accompanied by self-doping of La $5d$ bands for $x>0.2$. The results indicate robust in-plane spin and charge fluctuations that organize into stripe-like correlations whose strength is enhanced by moderate electron doping, and they suggest a Lifshitz-driven mechanism for these fluctuations. These findings echo bilayer Hubbard model predictions, implying that doping-tuned stripe fluctuations may play a key role in the emergence of superconductivity in LNO under pressure.

Abstract

Using the DFT+dynamical mean-field theory approach we study the effects of electronic correlations and doping on the normal state electronic structure of the double-layer nickelate superconductor La$_3$Ni$_2$O$_7$ under pressure. In agreement with experiments, we obtain significant orbital-dependent quasiparticle renormalizations of the Ni $x^2-y^2$ and $3z^2-r^2$ bands, accompanied by incoherence (bad metal behavior) of the $3z^2-r^2$ states, caused by the proximity of the Ni $3d$ states to orbital-dependent localization. Our results demonstrate a sensitive, non-monotonic dependence of $m^*/m$ on doping, with a remarkable, by about 20\%, increase for the Ni $x^2-y^2$ orbitals upon electron doping $x \sim 0.2$ (per Ni ion), implying a significant enhancement of orbital-dependent correlations with oxygen deficiency in LNO. We observe a reconstruction of the low-energy electronic structure of LNO upon doping above $x\sim -0.3$ and 0.2. It is associated with the Lifshitz transition, with a crossover to a self-doping regime characterized by partial occupation of the La $5d$ bands (upon an electron doping $x>0.2$). Our analysis of the static magnetic susceptibility $χ({\bf q})$ obtained within DFT+DMFT suggests the possible formation of the spin and charge (or bond) density wave stripes, implying strong spin and charge correlations in LNO. We show that this behavor is associated with suppression of the Néel $G$-type antiferromagnetic ordering of the Ni$^{2+}$ ions upon hole doping. Interestingly, upon a moderate electron doping of the Ni$^{2.5+}$ ions (e.g., with oxygen deficiency), we find a significant enhancement of the strength of in-plane spin and charge fluctuations. We note a close resembles of our results to those for the bilayer Hubbard model, which shows the boosting of superconductivity as one of the two electron bands approaches the Lifshitz transition (e.g., upon doping).

Figures (7)

• Figure 1: k-resolved spectral functions of PM LNO as a function of doping obtained using DFT+DMFT with $U=6$ eV and $J=0.95$ eV at $T = 116$K. The calculations are performed for the high-pressure orthorhombic crystal structure (determined experimentally at $\sim$30 GPa) with optimized atomic positions. We compare DFT+DMFT spectral functions with the nonmagnetic DFT results (shown with green broken lines).
• Figure 2: Orbital-dependent spectral functions of PM LNO as a function of doping obtained by DFT+DMFT at $T=116$K . The partial Ni $t_{2g}$, $x^2 - y^2$, and $3z^2 - r^2$ orbital contributions are shown (per orbital). The partial Ni $x^2 - y^2$, and $3z^2 - r^2$ orbital states are magnified by a factor 3 for better readability.
• Figure 3: Ni $e_g$ orbital occupations, instantaneous ($\sqrt{\hat{m}^2_z}$) and fluctuating ($M_\mathrm{loc}$) local magnetic moments as a function of doping calculated by DFT+DMFT with $U=6$ eV and $J=0.95$ eV at T=116 K. The fluctuating magnetic moments evaluated as $M_\mathrm{loc}=[k_BT \int \chi(\tau) d\tau ]^{1/2}$), where $\chi(\tau) \equiv \langle \hat{m}_z(\tau)\hat{m}_z(0) \rangle$ is the local spin-spin correlation function.
• Figure 4: Our results for the weights of differnt atomic configururations (left panel: for the Ni $3d^7$, $3d^8$ and $3d^9$ valence configurations; right panel: for the spin-state $S=0$, $S=1/2$ and $S=1$ configurations) of the Ni $3d$ electrons calculated using DFT+DMFT for PM LNO at $T = 116$K as a function of doping.
• Figure 5: Quasiparticle Fermi surfaces [spectral function $A( {\bf k}, \omega)$ evaluated at $\omega = 0$] for ${\bf k}_z=0$ (top panel) and ${\bf k}_z=\pi/c$ (bottom panel) calculated using DFT+DMFT for PM LNO at $T = 116$ K for different doping levels.