Electronic structure of La_2-2xSr_1+2xMn ₂O₇ studied by x-ray photoemission spectroscopy

We have studied the electronic structure of La_2-2xS _1+2xMn₂O₇ with x=0.4 and 0.5 by means of x-ray photoemission spectroscopy (XPS). In going from x=0.4 to x=0.5, the O 1s, Mn 2p, and valence-band spectra show an energy shift of ∼0.2 eV toward the Fermi level that is consistent with the hole doping in the e_g band. The spectral weight at the Fermi level is considerably suppressed for x=0.4 and 0.5, indicating that the e_g electron has polaronic character as pointed out by Dessau et al. Also, photoemission measurements have been done for the samples illuminated with laser light to probe photoinduced change of the electronic structure. While the O 1s spectrum of the x=0.4 sample is shifted by 0.1 eV to the higher binding energy side, that of x=0.5 is shifted by 0.7 eV. This would be related to the phase competition between the CE-type and A-type antiferromagnetic states and the unusual electron-lattice coupling found in x=0.5.