Electrodynamics of the vanadium oxidesVO2andV2O3

Abstract

The optical and infrared properties of films of vanadium dioxide ͑VO 2 ͒ and vanadium sesquioxide ͑V 2 O 3 ͒ have been investigated via ellipsometry and near-normal incidence reflectance measurements from far infrared to ultraviolet frequencies. Significant changes occur in the optical conductivity of both VO 2 and V 2 O 3 across the metal-insulator transitions at least up to ͑and possibly beyond͒ 6 eV. We argue that such changes in optical conductivity and electronic spectral weight over a broad frequency range are evidence of the important role of electronic correlations to the metal-insulator transitions in both of these vanadium oxides. We observe a sharp optical transition with possible final state ͑exciton͒ effects in the insulating phase of VO 2 . This sharp optical transition occurs between narrow a 1g bands that arise from the quasi-one-dimensional chains of vanadium dimers. Electronic correlations in the metallic phases of both VO 2 and V 2 O 3 lead to reduction of the kinetic energy of the charge carriers compared to band theory values, with paramagnetic metallic V 2 O 3 showing evidence of stronger correlations compared to rutile metallic VO 2 .

Modification of electronic structure in compressively strained vanadium dioxide films

“…Some of the lower energy inter-band transitions in this compressively strained sample differ significantly from those measured previously on bulk VO 2 and thin films. [12][13][14]19 The VO 2 film on quartz exhibits a broad Drude-like metallic response "q" and an interband transition "s" which are consistent with previous works. Feature "s" at 3.1 eV is attributed to transitions between the orbitals and the vanadium bands.…”

“…The dimerization would lead to a splitting of the orbitals into bonding ( and anti-bonding bands, while the antiferroelectric tilting of the vanadium pairs would lead to an upshift of the orbitals away from the Fermi energy to produce a gap between the filled bonding band and the empty band 11 . This effective band-structure scheme is qualitatively supported by experimental data on bulk crystals and thin films [12][13][14] . However, a precise quantitative understanding of how this scheme is realized-in particular the roles of electronic correlations and the structural instability in the MIT-remains a matter of debate.…”

“…Subtle evidence of a transition between the Hubbard bands was seen previously in rutile VO 2 on sapphire near 3 eV. 13 However, this feature could not be clearly resolved from the O to transition. Thus, it's also possible that this feature has in fact been shifted to a lower energy in our particular film.…”

“…Previous infrared and optical spectroscopy experiments have been performed on bulk VO 2 and thin films. [12][13][14]19,20 However, VO 2 films grown on different substrates and by different techniques can have significantly different strain states and microstructure. Because of the extreme sensitivity to external parameters in strongly correlated systems mentioned previously, accurate characterization of the strain and microstructure of various films, and the resultant emergent properties, can provide additional insight into the physics of these materials.…”

Dynamical gap and cupratelike physics from holography

“…It points to strong correlations being the source of the gap rather than the breaking of some spontaneous symmetry as in the case of superconductivity. Optical conductivity studies [30] reveal that spectral weight as far away as 6 eV contributes to the formation of the Drude peak at zero frequency once the Mott gap closes. Such UV-IR mixing is a ubiquitous feature of Mott systems.…”