Resonant photoemission spectroscopy study of impurity-induced melting in Cr- and Ru-doped ${\mathrm{Nd}}_{1/2}{A}_{1/2}\mathrm{Mn}{\mathrm{O}}_3(A=\mathrm{Ca},\mathrm{Sr})$

Electronic structures of very dilute Cr- or Ru-doped ${\mathrm{Nd}}_{1/2}{A}_{1/2}{\mathrm{MnO}}_3$ (NAMO) $(A=\mathrm{Ca},\mathrm{Sr})$ manganites have been investigated using the Mn and Cr $2\overrightarrow{p}3d$ resonant photoemission spectroscopy (PES). All the Cr- and Ru-doped NAMO systems exhibit the clear metallic Fermi edges in the Mn $e_g$ spectra near $E_F,$ consistent with their metallic ground states. The Cr $3d$ states with $t_{2g}^3$ configuration are at $\sim 1.3\mathrm{eV}$ below $E_F,$ and the Cr $e_g$ states do not participate in the formation of the band near $E_F.$ Cr- and Ru-induced ferromagnetism and insulator-to-metal transitions can be understood based on their measured electronic structures.