Phys. Rev. B 76, 205123 (2007) [4 pages]Temperature-dependent photoemission and x-ray absorption studies of the metal-insulator transition in Bi1−xLaxNiO3Received 13 July 2007; revised 22 October 2007; published 29 November 2007 Perovskite-type BiNiO3 is an insulating antiferromagnet in which a charge disproportionation occurs at the Bi site. La substitution for Bi suppresses the charge disproportionation and makes the system metallic, and for 0.05≤x≤0.1 a broad metal-insulator transition (MIT) occurs as a function of temperature. We have measured the temperature dependence of the photoemission and x-ray absorption (XAS) spectra of Bi1−xLaxNiO3 to investigate how the electronic structure changes across the MIT. From the Ni 2p XAS spectra of x=0.05, we found almost no change in the valence of Ni across the MIT. In the valence-band photoemission spectra, the Fermi cutoff disappeared for x=0.05 at a low temperature, whereas for x=0.1 and 0.2, it remained at all temperatures but the intensity at the Fermi level decreased gradually with decreasing temperature. Our experimental results suggest that the MIT is caused by the localization of holes in the O 2p band and that the “insulating” phase below the MIT is indeed a mixture of insulating and metallic regions. © 2007 The American Physical Society URL:
http://link.aps.org/doi/10.1103/PhysRevB.76.205123
DOI:
10.1103/PhysRevB.76.205123
PACS:
71.28.+d, 71.30.+h, 79.60.−i, 78.70.Dm
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