Temperature-dependent photoemission and x-ray absorption studies of the metal-insulator transition in Bi1-x Lax Ni O3

Hiroki Wadati, Kiyohisa Tanaka, Atsushi Fujimori, Takashi Mizokawa, Hiroshi Kumigashira, Masaharu Oshima, Shintaro Ishiwata, Masaki Azuma, Mikio Takano

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Abstract

Perovskite-type BiNi O3 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-x Lax Ni O3 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.

Original languageEnglish
Article number205123
JournalPhysical Review B - Condensed Matter and Materials Physics
Volume76
Issue number20
DOIs
Publication statusPublished - 2007 Nov 29
Externally publishedYes

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Metal insulator transition
Photoemission
x ray absorption
photoelectric emission
insulators
X rays
metals
x ray spectra
Absorption spectra
Temperature
temperature
valence
absorption spectra
Valence bands
Fermi level
Perovskite
Electronic structure
Substitution reactions
cut-off
substitutes

ASJC Scopus subject areas

  • Condensed Matter Physics

Cite this

Temperature-dependent photoemission and x-ray absorption studies of the metal-insulator transition in Bi1-x Lax Ni O3. / Wadati, Hiroki; Tanaka, Kiyohisa; Fujimori, Atsushi; Mizokawa, Takashi; Kumigashira, Hiroshi; Oshima, Masaharu; Ishiwata, Shintaro; Azuma, Masaki; Takano, Mikio.

In: Physical Review B - Condensed Matter and Materials Physics, Vol. 76, No. 20, 205123, 29.11.2007.

Research output: Contribution to journalArticle

Wadati, Hiroki ; Tanaka, Kiyohisa ; Fujimori, Atsushi ; Mizokawa, Takashi ; Kumigashira, Hiroshi ; Oshima, Masaharu ; Ishiwata, Shintaro ; Azuma, Masaki ; Takano, Mikio. / Temperature-dependent photoemission and x-ray absorption studies of the metal-insulator transition in Bi1-x Lax Ni O3. In: Physical Review B - Condensed Matter and Materials Physics. 2007 ; Vol. 76, No. 20.
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AB - Perovskite-type BiNi O3 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-x Lax Ni O3 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.

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