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The layered Mott insulator TiOCl with Ti in a 3d1 configuration exhibits two phase transitions at 67K and 95K, respectively. While from susceptibility [1], specific heat [2], and diffraction data [3] the 67K transition can be understood in terms of a (non-canonical) spin-Peierls transition [1], the nature of the other transition, also seen in the specific heat and susceptibility measurements, is still unknown. In particular, a possible relationship to the transition at lower temperature has not yet been clarified. LDA+U [4] calculations predict a valence band predominantly consisting of Ti 3dxy orbitals which overlap along the crystallographic b-direction to form linear chains.
We have performed polarization dependent angle resolved photoemission measurements along the two mutually perpendicular a and b axes to determine both the dimensionality and symmetry of the valence band. The experimental spectral function is compared to LDA+U [4], LDA+DMFT [5], NMTO+DMFT [6] calculations, and the 1D Hubbard model.
[1] Seidel A, Marianetti CA, Chou FC, Ceder G, Lee PA, Phys. Rev. B 67, 020405 (2003) [2] Shaz A, van Smaalen S., Palatinus L, Hoinkis M, Klemm M, Horn S, Claessen R, submitted (2004) [3] Hemberger J, Hoinkis M, Klemm M, Sing M, Claessen R, Horn S, Loidl A, cond-mat/0501517 [4] Saha-Dasgupta T, Valenti R, Rosner H, Gros C, Europhys. Lett. 67, 63 (2004) [5] Craco L, Laad MS, Müller-Hartmann E, cond-mat/0410472 [6] Saha-Dasgupta T, Lichtenstein A, Valenti R, cond-mat/0411631 |