Observation of the Gap and Kinetic Energy in a Correlated Insulator

Abstract

Fundamental energies are determined optically for an ensemble of correlated electrons in an antiferromagnetic insulator, V203. The observed variation of the energy gap and the kinetic energy are compared quantitatively to some approximate solutions of the Hubbard Hamiltonian.PACS numbers: 71.27.+a, 71.30.+h, 78.30.Hv The approach to the metal-insulator transition by a collection of correlated electrons has been a subject of considerable interest since Mott's classic paper [1] We have made measurements with energy resolution less than 1 meV on crystals which we found to be very difficult to anneal, polish, and etch, with the additional difficulty that they crack on passing through the metalinsulator transition that occurs on cooling from room temperature.Based on optical and dc transport characterization of over 10 crystals, we have developed annealing and surface preparation procedures which yield reproducible spectra [17]. We have made reflectivity, R, measurements from the far-infrared to E = 3.5 eV (a frequency, ta, about 27000 crn ') and used the measurements of Shin et al. [18] from 3.5 to 25 eV in our Kramers-Kronig transformations to obtain the optical conductivity, tr.The main part of Fig. 1 [4,5]) which can introduce conducting states into a filled band, and it also differs from disordered doping which primarily introduces impurity states into the gap [1]. We see negligible absorption (except that due to phonons) in the energy gap, and our 0. extrapolated to E = 0 agrees with the (essentially zero) measured dc conductivity, trd"of similarly prepared samples.Qualitatively, the spectra show an energy gap, 2b"with a "soft" edge and a broad peak at higher energy. This

Calculation of metallic and insulating phases of V2O3 by hybrid density functionals

“…19,21,22 The magnetic moment of the V atom is calculated to be 1.8 μ B , close to the LDA+U value 17 of 1.7 μ B . The spin is automatically relaxed in the spin-polarized calculation, thus this value identifies the S = 1 local moment as the ground state, consistent with experiment 58 and previous analysis, 59,17 and contrary to the Castellini model. 60 Fig 5(b) shows the band structure of the AFI phase.…”

Transfer of spectral weight in spectroscopies of correlated electron systems

“…In Fig.14 we display the results for the size of the gaps ∆, which are in excellent agreement with the experimental results indicated by black squares 42 . It is interesting to note that the results of Fig.14, shown for various degrees of magnetic frustration, indicate that in V 2 O 3 frustration plays an important role.…”

Properties of oxide thin films and their adsorption behavior studied by scanning tunneling microscopy and conductance spectroscopy

“…4.38A). The bare, vanadyl-terminated oxide film exhibits a region of zero-conductance around the Fermi level, which reflects the V 2 O 3 correlation gap in the V-3d band that opens below the Mott-transition at 150 K. 263,435,436 The gap size amounts to 0.5-0.7 eV, and exhibits small spatial modulations due to local differences in the stoichiometry of the individual oxide grains (see also Fig. 3.7).…”