Münster 1999 – wissenschaftliches Programm

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TT: Tiefe Temperaturen

TT 20: Metall-Isolator-Überg
änge

TT 20.7: Vortrag

Donnerstag, 25. März 1999, 17:00–17:15, F2

Octahedral deformations and the metal-insulator transition in VO₂ — •V. Eyert^1,2, W.-D. Yang², and K.-H. H"ock² — ¹Hahn-Meitner-Institut, D-14109 Berlin — ²Institut f"ur Physik, Universit"at Augsburg, D-86135 Augsburg

The classical metal-insulator transition in VO₂ is accompanied by two fundamental structural distortions of the characteristic vanadium chains, namely, a V-V dimerization and a zigzag-like antiferroelectric V displacement. We present results of electronic structure calculations using both the structures of the rutile and the monoclinic M₁ phases. They reveal strong bonding-antibonding splitting of the V 3d_x²−y² states due to the dimerization and upshift of the remaining t_2g bands due to the antiferroelectric mode. Additional calculations for the metastable insulating monoclinic M₂ phase of VO₂ , where only half of the chains dimerize, result in a similar picture on these chains, while electronic states on the other chains exhibit a band splitting due to antiferromagnetic order. Either type of symmetry breaking opens a way to the observed insulating behaviour. However, due to limitations of the local density approximations, opening of the bandgap is still incomplete. The metal-insulator transition of VO₂ thus arises predominantly from structural instabilities of the rutile phase which may be assisted by electronic correlations.