23 research outputs found
The Metal-Insulator Transition of NbO2: an Embedded Peierls Instability
Results of first principles augmented spherical wave electronic structure
calculations for niobium dioxide are presented. Both metallic rutile and
insulating low-temperature NbO2, which crystallizes in a distorted rutile
structure, are correctly described within density functional theory and the
local density approximation. Metallic conductivity is carried to equal amounts
by metal t_{2g} orbitals, which fall into the one-dimensional d_parallel band
and the isotropically dispersing e_{g}^{pi} bands. Hybridization of both types
of bands is almost negligible outside narrow rods along the line X--R. In the
low-temperature phase splitting of the d_parallel band due to metal-metal
dimerization as well as upshift of the e_{g}^{pi} bands due to increased p-d
overlap remove the Fermi surface and open an optical band gap of about 0.1 eV.
The metal-insulator transition arises as a Peierls instability of the
d_parallel band in an embedding background of e_{g}^{pi} electrons. This basic
mechanism should also apply to VO2, where, however, electronic correlations are
expected to play a greater role due to stronger localization of the 3d
electrons.Comment: 4 pages, revtex, 6 eps figures, additional material avalable at
http://www.physik.uni-augsburg.de/~eyert
Fermi surface of MoO2 studied by angle-resolved photoemission spectroscopy, de Haas-van Alphen measurements, and electronic structure calculations
A comprehensive study of the electronic properties of monoclinic MoO2 from
both an experimental and a theoretical point of view is presented. We focus on
the investigation of the Fermi body and the band structure using angle resolved
photoemission spectroscopy, de Haas-van Alphen measurements, and electronic
structure calculations. For the latter, the new full-potential augmented
spherical wave (ASW) method has been applied. Very good agreement between the
experimental and theoretical results is found. In particular, all Fermi surface
sheets are correctly identified by all three approaches. Previous controversies
concerning additional hole-like surfaces centered around the Z- and B-point
could be resolved; these surfaces were an artefact of the atomic-sphere
approximation used in the old calculations. Our results underline the
importance of electronic structure calculations for the understanding of MoO2
and the neighbouring rutile-type early transition-metal dioxides. This includes
the low-temperature insulating phases of VO2 and NbO2, which have crystal
structures very similar to that of molybdenum dioxide and display the
well-known prominent metal-insulator transitions.Comment: 17 pages, 21 figures, more information at
http://www.physik.uni-augsburg.de/~eyert