One-dimensional versus two-dimensional correlation effects in the   oxyhalides TiOCl and TiOBr
  We have performed a comparative study of the electronic structures of the spin-Peierls systems TiOCl and TiOBr by means of photoemission spectroscopy and density functional calculations. While the overall electronic structure of these isostructural compounds is qualitatively similar, the bromide appears to be less one-dimensional. We present a quantitative analysis of the experimental dispersions in terms of exchange constant J and hopping integral t as well as a discussion of the qualitative spectral features. From that we conclude that despite the one-dimensional physics triggering the ground state in both compounds a proper description of the normal state electronic structure has to take into account the anisotropic frustrated interchain interactions on the underlying triangular lattice. 
M. Hoinkis, M. Sing, S. Glawion, L. Pisani, R. Valenti, S. van   Smaalen, M. Klemm, S. Horn, and R. Claessen