Mechanism and observation of Mott transition in VO2-based two- and three-terminal devices
When holes of about 0.018% are induced into a conduction band (breakdown of critical on-site Coulomb energy), an abrupt first-order Mott metal–insulator transition (MIT) rather than a continuous Hubbard MIT near a critical on-site Coulomb energy U / U c =1, where U is on-site Coulomb energy between electrons, is observed on an inhomogeneous VO 2 film, a strongly correlated Mott insulator. As a result, discontinuous jumps of the density of states on the Fermi surface are observed and inhomogeneity inevitably occurs. The off-current and temperature dependences of the abrupt MIT in a two-terminal device and the gate effect in a three-terminal device are clear evidence that the abrupt Mott MIT was induced by the excitation of holes. Raman spectra measured by a micro-Raman system show an MIT without the structural phase transition. Moreover, the magnitude of the observed jumps Δ J observed at the abrupt MIT is an average over an inhomogeneous measurement region of the maximum true jump, Δ J true , deduced from the Brinkman–Rice picture. A brief discussion of whether VO 2 is a Mott insulator or a Peierls insulator is presented.