Competition between instabilities of Peierls transition and Mott transition in W-doped VO₂ thin films

The change in electronic structure of V_1-xW_xO ₂ thin films across a metal-insulator transition (MIT) is investigated in terms of hard x-ray photoemission spectroscopy and x-ray absorption spectroscopy. In the lower doping range (0 ≤ x ≤ 0.08), the spectra exhibit the characteristic features for the dimerization of V ions in the monoclinic phase, indicating that Peierls-like instability predominately causes the MIT in this range. Conversely, in the higher doping range (0.1 ≤ x), spectral weight transfer is observed from the coherent part at the Fermi level to the incoherent part, indicating that the ground state of V _1-xW_xO₂ films in this range is a typical Mott insulator. The results suggest that the unusual phase diagram of the V _1-xW_xO₂ thin films originates from the competition between the Peierls and Mott instabilities.