Electronic structure of $\mathrm{Pr}\mathrm{Co}{\mathrm{O}}_3$ and its temperature evolution

We investigate the detailed electronic structure of $\mathrm{Pr}\mathrm{Co}{\mathrm{O}}_3$ and its temperature evolution by using high-resolution photoemission spectroscopy and ab initio band structure calculations. We observe that, in addition to the correlation effect, spin-orbit interaction plays an important role in determining the electronic properties of this system. $\mathrm{Pr}4f$ states are found to be strongly hybridized with the $\mathrm{O}2p$ and $\mathrm{Co}3d$ valence electronic states and appear in the vicinity of the Fermi level. The calculated results corresponding to the intermediate spin state of Co provide a good representation of the experimental spectra at $300\mathrm{K}$. The decrease in temperature from $300\mathrm{K}$ leads to a gradual enhancement of the $\mathrm{O}2p$ character in the bonding features, indicating the signature of an enhancement of the low spin state contributions at lower temperatures. The temperature evolution of the shift of the valence band edge is found to be consistent with the transport data.

Figure 1

(Color online) $\mathrm{O}1s$ core level spectra recorded at $300\mathrm{K}$ (solid circles) and $150\mathrm{K}$ (hollow circles). The shaded region shows the impurity contributions.

Figure 2

(Color online) (a) $\mathrm{O}2p$ (dashed line) and $\mathrm{Co}3d$ partial density of states having $t_{2g}$ (thin solid line) and $e_g$ (thick solid line) symmetries. (b) $\mathrm{Pr}4f$ partial density of states obtained from GGA calculation. (c) $\mathrm{O}2p$ (dashed line) and $\mathrm{Co}3d$ partial density of states having $t_{2g}$ (thin solid line) and $e_g$ (thick solid line) symmetries. (d) $\mathrm{Pr}4f$ partial density of states obtained from GGA calculation including SOC.

Figure 3

(Color online) (a) $\mathrm{O}2p$ (dashed line) and $\mathrm{Co}3d$ partial density of states having $t_{2g}$ (thin solid line) and $e_g$ (thick solid line) symmetries and (b) $\mathrm{Pr}4f$ partial density of states obtained from $\mathrm{GGA}+U$ calculation when on-site Coulomb correlation between $\mathrm{Co}3d$ electrons is considered. (c) $\mathrm{O}2p$ (dashed line) and $\mathrm{Co}3d$ partial density of states having $t_{2g}$ (thin solid line) and $e_g$ (thick solid line) symmetries and (d) $\mathrm{Pr}4f$ partial density of states obtained from GGA calculation when on-site Coulomb correlation between $\mathrm{Co}3d$ and $\mathrm{Pr}4f$ electrons is considered. In all the calculations, SOC is included.

Figure 4

(Color online) Calculated $\mathrm{Pr}4f$ (thin solid line), $\mathrm{Co}3d$ (thick solid line), and $\mathrm{O}2p$ (dashed line) partial density of states corresponding to (a) LS, (b) IS, and (c) HS configurations using $\mathrm{GGA}+U$ method including spin-orbit coupling.

Figure 5

(Color online) Experimental valence band spectra collected at room temperature using $\mathrm{Al}K\alpha$, $\mathrm{He}\mathrm{II}$, and $\mathrm{He}\mathrm{I}$, radiations. The lines denote the calculated $\mathrm{Pr}4f$ (thin solid line), $\mathrm{Co}3d$ (thick solid line), and $\mathrm{O}2p$ (dashed line) partial density of states corresponding to the intermediate spin configuration of a Co ion obtained from $\mathrm{GGA}+U$ calculation including spin-orbit coupling. Room temperature experimental valence band spectrum of $\mathrm{La}\mathrm{Co}{\mathrm{O}}_3$ recorded by using $\mathrm{Al}K\alpha$ radiation is also shown by hollow circles.

Figure 6

(Color online) (a) Valence band spectra collected at $300\mathrm{K}$ (hollow circles) and $150\mathrm{K}$ (plus signs) using $\mathrm{Al}K\alpha$ radiation. (b) Valence band spectra collected at $300\mathrm{K}$ (hollow circles), $250\mathrm{K}$ (solid circles), $200\mathrm{K}$ (solid triangles), and $150\mathrm{K}$ (plus signs) using $\mathrm{He}\mathrm{II}$ radiation. (c) Spectra collected at $300\mathrm{K}$ (hollow circles), $250\mathrm{K}$ (solid circles), $200\mathrm{K}$ (solid triangles), and $150\mathrm{K}$ (plus signs) in the narrow region of the Fermi level using $\mathrm{He}\mathrm{II}$ radiation. Solid lines in (a) and (b) indicate the contribution from $\mathrm{O}2p$ states.

Figure 7

(Color online) $\mathrm{Co}3d$ and $\mathrm{Pr}4f$ contributions extracted (a) from the XP spectra at $300\mathrm{K}$ (solid triangles) and $150\mathrm{K}$ (plus signs), and (b) from the $\mathrm{He}\mathrm{II}$ spectra at $300\mathrm{K}$ (solid triangles), $225\mathrm{K}$ (hollow circles), and $150\mathrm{K}$ (plus signs). Temperature evolution of the spectra in the vicinity of the Fermi level is shown in (c) and the band gap obtained from resistivity data is shown in (d).

Figure 8

(Color online) $\mathrm{Pr}5p$ (solid line) and $\mathrm{O}2s$ (dashed line) PDOSs calculated using the (a) LS, (b) IS, and (c) HS configurations of a Co ion.

Figure 9

(Color online) (a) Background subtracted $\mathrm{La}5p$ and $\mathrm{O}2s$ core level spectra collected at $300\mathrm{K}$ using $\mathrm{Al}K\alpha$ (hollow circles) and $\mathrm{Mg}K\alpha$ (solid lines). (b) Calculated $\mathrm{Pr}5p$ (solid lines) and $\mathrm{O}2s$ (dashed lines) PDOSs corresponding to the IS state configuration.