Electronic structure of antiferromagnetic $\mathrm{La}\mathrm{Mn}{\mathrm{O}}_3$ and the effects of charge polarization

The electronic structure of $A$-type antiferromagnetic insulator $\mathrm{La}\mathrm{Mn}{\mathrm{O}}_3$ is investigated by the GW approximation. The band gap and spectrum are in a good agreement with experimental observation. The lifetime of electrons in conduction bands is much shorter than that of holes in valence bands. The insulator-to-metal transition with antiferromagnetic-to-ferromagnetic transition with photocarrier injection is attributed to the characteristic properties of excited electron states in $A$-type antiferromagnetic perovskite systems. The onsite $d\text{−}d$ Coulomb interaction is strongly screened at the low energy region by mobile $e_g$ electrons.

Figure 1

Energy band of $A\text{−}\mathrm{AF}$ $\mathrm{La}\mathrm{Mn}{\mathrm{O}}_3$: (a) LSDA $\left({ϵ}_{\mathbf{k}n}\right)$, and (b) GWA $\left(E_{\mathbf{k}n}\right)$. The energy zeroth is fixed at the top of the respective valence band.

Figure 2

The individual contribution to the correction of the self-energy $\Delta {\Sigma }_{\mathbf{k}n}\left({ϵ}_{\mathbf{k}n}\right)$ as a function of the LSDA eigenenergies ${ϵ}_{\mathbf{k}n}$. The energy zeroth is fixed at the top of the LSDA valence band. Crosses (+): ${\Sigma }^{\mathrm{c}}$, open circles (엯): ${\Sigma }^{\mathrm{x}}$, dots (●): $V^{\mathrm{xc}}$.

Figure 3

(Color) (a) Total DOS of LSDA, (b) total DOS of the GW quasiparticles $E_{\mathbf{k}n}$, and the absolute value of the imaginary part of the Green’s function $(1∕\pi )\mid \mathrm{Im}G\mid$ for (c) the total and (d) the partial components of $(1∕\pi )\mid \mathrm{Im}G\mid$ on one respective atom. In (d), the upper and the lower panels show the partial components with majority and minority spins, and bold solid line: $\mathrm{Mn}\text{−}{d}_{3z^2-r^2}$, bold broken line: $\mathrm{Mn}\text{−}{d}_{x^2-y^2}$, bold dot-chain line: $\mathrm{Mn}\text{−}d\left(t_{2g}\right)$, thin dotted line: $\mathrm{O}1\text{−}p$, thin solid line: $\mathrm{O}2\text{−}p$, thin dot-chain line: $\mathrm{La}\text{−}d$, thin broken line: $\mathrm{La}\text{−}f$. The energy zeroth in (a) is fixed at the top of the valence bands of LSDA and in $\left(\mathrm{b}\right)–\left(\mathrm{d}\right)$ at that of GWA.

Figure 4

(a) The self-energy of the highest valence $\left(\Delta {\Sigma }_{\mathrm{v}}\right)$ and lowest conduction $\left(\Delta {\Sigma }_{\mathrm{c}}\right)$ bands of the majority spin at $\Gamma$ point (solid line: real part, dotted line: imaginary part). The energy zeroth is set at the top of the GWA valence band and the GWA quasiparticle energies are indicated by arrows. Inset shows the enlarged self-energy near the energy zeroth. (b) The behavior of the self-energy of several bands at $\Gamma$ point near the band gap. The bands are numbered from the bottom and $n=56$ and $n=57$ are the highest valence and lowest conduction bands, respectively. We find rapid increase of the absolute values of the imaginary parts, corresponding to enhanced widths in the Green’s functions.

Figure 5

(Color online) The imaginary part of the Green’s function at $\mathbf{k}=0$ for the respective LSDA band ${ϵ}_{\mathbf{k}n}$. The energy zeroth is set at the top of the GWA valence band and the zeroth of the LSDA bands ${ϵ}_{\mathbf{k}n}$ is at the top of the LSDA valence band. The peak height higher than five is not shown.

Figure 6

The dynamically screened Coulomb interaction, both real and imaginary parts. Solid line: interaction with majority spins, dotted line: interaction with minority spins.