Resonant inelastic x-ray scattering study of the hole-doped manganites ${\mathrm{La}}_{1-x}{\mathrm{Sr}}_x{\mathrm{MnO}}_3$ ($x=0.2$, 0.4)

Electronic excitations in the hole doped manganese oxides (${\mathrm{La}}_{1-x}{\mathrm{Sr}}_x{\mathrm{MnO}}_3$, $x=0.2$ and 0.4) have been elucidated by using the resonant inelastic x-ray scattering method. A doping effect in the strongly correlated electron systems has been observed. The scattering spectra show that a salient peak appears in low energies indicating the persistence of the Mott gap. At the same time, the energy gap is partly filled by doping holes and the spectral weight energy shifts toward lower energies. The excitation spectra show little change in the momentum space as is in undoped ${\mathrm{LaMnO}}_3$. On the other hand, the scattering intensities in the low-energy excitations of $x=0.2$ are anisotropic in temperature dependence, which indicates an anisotropy of magnetic interaction and underlying effect of the orbital.

Figure 1

Electronic phase diagram of ${\mathrm{La}}_{1-x}{\mathrm{Sr}}_x{\mathrm{MnO}}_3$ for the $\mathrm{Sr}$ concentration $\left(x\right)$ and temperature $\left(T\right)$ from Ref. 10. The filled circles and the arrow indicate the observed points in Figs. 3, 6, respectively.

Figure 2

Resonant inelastic x-ray scattering spectra of ${\mathrm{La}}_{0.6}{\mathrm{Sr}}_{0.4}{\mathrm{MnO}}_3$ as a function energy loss at some representative incident x-ray energies $\left(E_i\right)$. The energy resolution is about $500\mathrm{meV}$, and the scattering vector is fixed at $\mathit{Q}=(2.7,0,0)$. Three resonantly enhanced excitations are indicated by the arrows. The strong intensity above $10\mathrm{eV}$ in the spectrum of $E_i=6.550\mathrm{keV}$ comes from the $\mathrm{Mn}$ $K{\beta }_5$ emission line.

Figure 3

Resonant inelastic x-ray scattering spectra of ${\mathrm{La}}_{1-x}{\mathrm{Sr}}_x{\mathrm{MnO}}_3$ $\left(x=0,0.2,0.4\right)$. The energy resolution is about $230\mathrm{meV}$. (a) RIXS spectra at $\mathit{Q}=(2.7,0,0)$. The solid lines are fitting results assuming the elastic peak, three Lorentz functions for excitations, and fluorescence ($\mathrm{Mn}$ $K{\beta }_5$ line). (b) The excitation in the low-energy region measured at high scattering angle.

Figure 4

(a): The RIXS spectra of ${\mathrm{La}}_{0.6}{\mathrm{Sr}}_{0.4}{\mathrm{MnO}}_3$ at various scattering vectors. The energy resolution is about $230\mathrm{meV}$. Solid circles are observed points. Solid and dashed lines are the results of fitting of overall spectra and excitations from LHB to UHB, respectively. (b) Dispersion relation of the excitation from the LHB to the UHB.

Figure 5

Azimuthal angle $\left(\psi \right)$ dependence of ${\mathrm{La}}_{0.6}{\mathrm{Sr}}_{0.4}{\mathrm{MnO}}_3$. The open circles and squares are the scattering intensity of the energy transfer $2\mathrm{eV}$ at $\mathit{Q}=(2.7,0,0)$ and the fluorescence yield, respectively. The filled circles represent the scattering intensity divided by the fluorescence. The solid lines are the fitting result using a function of $A(1+B{\cos }^2\psi )$.

Figure 6

RIXS spectra of ${\mathrm{La}}_{0.8}{\mathrm{Sr}}_{0.2}{\mathrm{MnO}}_3$ at some temperatures. The energy resolution is about $500\mathrm{meV}$. The scattering vectors are $\mathit{Q}=(2.7,0,0)$ for (a) and (b), and $\mathit{Q}=(2.2,2.2,0)$ for (c) and (d).

Figure 7

Temperature dependence of the RIXS intensity at fixed energy transfer of $2.25\mathrm{eV}$ in ${\mathrm{La}}_{0.8}{\mathrm{Sr}}_{0.2}{\mathrm{MnO}}_3$. The arrow indicates the ferromagnetic transition temperature $\left(T_C\right)$.