Hard X-ray core-level photoemission of

¹ Soft X-ray Spectroscopy Laboratory, RIKEN/SPring-8 Mikazuki-cho, Sayo-gun, Hyogo 679-5148, Japan
² Coherent X-ray Optics Laboratory, RIKEN/SPring-8 Mikazuki-cho, Sayo-gun, Hyogo 679-5148, Japan
³ JASRI/SPring-8 - Mikazuki-cho, Sayo-gun, Hyogo 679-5198, Japan
⁴ HiSOR, Hiroshima University - Higashi-Hiroshima, Hiroshima 739-8526, Japan
⁵ Institute for Solid State Physics, University of Tokyo Kashiwa, Chiba 277-8581, Japan

Received: 10 August 2004
Accepted: 24 September 2004

Abstract

We study the Mott-Hubbard metal-insulator transition in single-crystal using hard X-ray () core-level photoemission spectroscopy (PES). HX-PES enables a bulk probe of the electronic structure in the paramagnetic metallic and antiferromagnetic insulating phases. Metallic shows additional features at low binding energy to the main peak of V , , and core levels, which vanish in the insulating phase. The low-binding-energy features in the metallic phase are also observed using soft X-rays (), but with a reduced relative intensity compared to the HX-PES spectrum. A model cluster calculation including core hole screening by coherent states at the Fermi level, reproduces the low-binding-energy features in the metallic phase. The O core level also shows spectral changes: the asymmetric line shape in the metallic phase transforms to a symmetric line shape in the insulating phase, consistent with the metal-insulator transition. The results indicate screening by coherent states is more effective in the bulk compared to the surface. HX-PES is, thus, a reliable probe of the electronic-structure changes across the metal-insulator transition in strongly correlated electron systems.