Doping Induced Spin State Transition in ${\mathrm{LaCoO}}_3$: Dynamical Mean-Field Study

Hole and electron doped ${\mathrm{LaCoO}}_3$ is studied using dynamical mean-field theory. The one-particle spectra are analyzed and compared to the available experimental data, in particular the x-ray absorption spectra. Analyzing the temporal spin-spin correlation functions we find the atomic intermediate spin state is not important for the observed Curie-Weiss susceptibility. Contrary to the commonly held view about the roles played by the $t_{2g}$ and $e_g$ electrons we find narrow quasiparticle bands of $t_{2g}$ character crossing the Fermi level accompanied by strongly damped $e_g$ excitations.

Figure 1

Left panel: The doping dependence (hole doping $<0$) of the orbital occupancy. The stars mark results obtained with fixed double-counting correction. Considering the FM order for $x=0.3$ changes the data by less than 5%. Right panel: The local spin-spin correlation functions: black (full line)—the undoped system, blue (dash-dotted line)—hole doping $x=0.1$, 0.2, 0.3 (corresponding to increasing magnitude), and green (dashed line)—electron doping of 0.2. The inset shows the doping dependence of $E_{\mathrm{dc}}$.

Figure 2

Atomic state correlation matrix ${\Pi }_{\alpha \beta }$ for the hole doping of $x=0.2$ with the contribution of the most abundant $d^6$, $d^7$, and $d^8$ states (see Ref. 22 for the notation). The numbers show the contributions to the local susceptibility $T{\chi }_{\mathrm{loc}}$ summed over the blocks.

Figure 3

Left panel: Orbitally resolved spectral density: Co $e_g$ (black), Co $t_{2g}$ (gray or red), O $p$ (shaded or shaded blue) for various dopings. Right panel: The corresponding $k$-resolved spectral functions along the high symmetry lines in the Brillouin zone depicted as color plots.

Figure 4

Left: The unoccupied O $p$ spectra (broadened with Lorentzian) for various hole dopings. Right: The experimental XAS spectra reproduced from Ref. 13.

Figure 5

Left panel: Orbitally resolved spectral density: Co $e_g$ (black), Co $t_{2g}$ (grey or red), O $p$ (shaded or shaded blue) for the ferromagnetic solution obtained at $T=580\mathrm{K}$ and hole doping $x=0.3$. (Minority spin densities are multiplied with $-1$). Right panel: The corresponding $k$-resolved spectra for the majority (top) and minority (bottom) polarization.