Coherent metallic screening in core-level photoelectron spectra for the strongly correlated oxides La${}_{1-x}$Ba${}_x$MnO${}_3$ and V${}_{1-x}$W_xO${}_2$

Coherent metallic screening structures shown in core-level photoemission spectra for strongly correlated oxide materials were studied by hard x-ray photoemission spectroscopy (HAXPES) and the configuration interaction (CI) theory based on the cluster model, including the coherent metallic screening process. For the La${}_{1-x}$Ba${}_x$MnO${}_3$ thin film, the normalized intensity of the coherent metallic screening structure ($I_S$) seen in the Mn 2$p$ core-level spectra was proportional to the square of the hybridization strength, ($V$*), between the transition metal 3$d$ and coherent metallic states. In contrast, the normalized $I_S$ seen in the V 2$p$ core-level spectra for the V${}_{1-x}$W${}_x$O${}_2$ thin film was not proportional to ($V$*). The different behaviors of the normalized $I_S$ for the La${}_{1-x}$Ba${}_x$MnO${}_3$ and V${}_{1-x}$W${}_x$O${}_2$ thin films as a function of $V$* were understood by the series of the CI cluster model calculation. From the CI cluster model calculation, we found that the charge transfer energy (Δ*) between the transition metal 3$d$ states and the coherent metallic states strongly affect the normalized $I_S$ in the 2$p$ core-level photoemission final states. Therefore, the behavior of the normalized $I_S$ in the 2$p$ core-level HAXPES is thus not simply explained by the change of $V$*. The electronic structure parameters such as Δ* and $V$* relating to the coherent metallic states strongly contribute to the variation of the normalized $I_S$ in the photoemission final states. In contrast, we found that the detailed $I_S$ evaluation in the core-level HAXPES experiments for materials, in which the coherent metallic screening structures appear, allows us to evaluate the value of $V$* when we have the experimental core-level spectra and the electronic structure parameters set for a reference material. We also found that the intensity at the Fermi level is proportional to ($V$*), as expected from the Anderson impurity model.

Figure 1

(a) Mn 2$p$ core-level HAXPES spectra of the La${}_{1-x}$Ba${}_x$MnO${}_3$ thin film with $x$ = 0.15 taken at various temperature [6]. (b) $I_S$ spectra obtained by subtracting the assumed tail spectrum from the Mn 2$p$ core-level HAXPES spectra.

Figure 2

(a) $I_S$ referred to the spectrum taken at 320 K as a function of (V*)², where $I_S$ was normalized by the Mn 2$p$ main peak intensity. (b) $I_S$ obtained by subtracting the assumed tail spectrum from the Mn 2$p$ core-level spectra as a function of (V*)², where $I_S$ was normalized by (I${}_{\mathrm{Mn}2p}-I_S$). The values of V* were obtained from Ref. [6].

Figure 3

Valence band HAXPES spectra in the vicinity of $E_F$ for the La${}_{1-x}$Ba${}_x$MnO${}_3$ thin film with $x$ = 0.15 taken at 28, 200, and 300 K.

Figure 4

V 2$p$ core-level HAXPES spectra for the V${}_{1-x}$W${}_x$O${}_2$ thin films with $x$ = 0.00 − 0.05 taken at 360 K. The spectra were normalized at $E_B$ = 515.94 eV for comparison.

Figure 5

Valence band HAXPES spectra in the vicinity of $E_F$ for the V${}_{1-x}$W${}_x$O${}_2$ thin films [17]. The spectra were normalized by the V 2$p$ core-level spectral intensity by a factor of ($1-x$).

Figure 6

Schematic energy diagram of the initial and final states in the Mn 2$p$ core-level photoemission for La${}_{1-x}$Ba${}_x$MnO${}_3$. The ground state is denoted by $g$ in the figure. The photoemission final states are denoted by $f_n$ with $n$ = 1–4. The electronic structure parameters of Δ = 4.5 eV, Δ* = 0.8 eV, $U_{dd}$ = 5.1 eV, $U_{dc}$ = 5.4 eV, and $V_{pd}$ = 2.94 eV were employed [6].

Figure 7

Calculated $I_S$ as a function of (V*)² for La${}_{1-x}$Ba${}_x$MnO${}_3$, where $I_S$ was normalized by (I${}_{\mathrm{Mn}2p}$ − $I_S$). The electronic structure parameters of Δ = 4.5 eV, Δ* = 0.8 eV, $U_{dd}=5.1$ eV, $U_{dc}$ = 5.4 eV, and $V_{pd}$ = 2.94 eV [6] were used as the fixed parameters for simplicity.

Figure 8

Schematic energy diagram of the initial and final states in the V 2$p$ core-level photoemission for V${}_{1-x}$W${}_x$O${}_2$. The ground state is denoted by $g$ in the figure. The photoemission final states are denoted by $f_n$ with $n$ = 1–6. The electronic structure parameters of Δ = 4.0 eV, Δ* = 0.2 eV, $U_{dd}$ = 4.5 eV, $U_{dc}$ = 6.5 eV, and $V_{pd}$ = 2.4 eV were employed [11].

Figure 9

(a) Calculated $I_S$ as a function of (V*)² and (b) as a function of V* for V${}_{1-x}$W${}_x$O${}_2$, where $I_S$ was normalized by (I${}_{\mathrm{V}2p}$ − $I_S$). The electronic structure parameters of Δ = 4.0 eV, Δ* = 0.2 eV, $U_{dd}$ = 4.5 eV, $U_{dc}$ = 6.5 eV, and $V_{pd}$ = 2.4 eV [11] were used as the fixed parameters for simplicity.

Figure 10

Relationship between the experimental $I$($E_F$) and evaluated (V*)² for La${}_{1-x}$Ba${}_x$MnO${}_3$. The solid line corresponds to the least-square-fitting result.

Figure 11

Relationship between the experimental $I$($E_F$) and evaluated (V*)² for V${}_{1-x}$W${}_x$O${}_2$. The solid line corresponds to the least-square-fitting result.