Berlin 2008 – scientific programme

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TT: Fachverband Tiefe Temperaturen

TT 34: Correlated Electrons: Metal-Insulator Transition 2

TT 34.6: Talk

Thursday, February 28, 2008, 15:15–15:30, H 2053

Spectral weight transfer upon doping in the low-dimensional Mott-Hubbard systems TiOCl and TiOBr — •Sebastian Glawion, Karin Goss, Markus Scholz, Michael Sing, and Ralph Claessen — Experimentelle Physik 4, Universität Würzburg, D-97074 Würzburg

Transition metal oxyhalides have seen increasing interest in the past few years due to their non-canonical phase transitions into incommensurate and commensurate spin-Peierls phases and their potential as prototypical 3d¹ Mott insulators. For pristine TiOCl and TiOBr, a transition into a metallic phase under pressure has been reported which, however, seems to be structurally driven. Using XPS and ARPES we investigated the possibility of band-filling controlled metal-insulator transitions using n- and p-type doping. The layered crystal structure allows for easy intercalation of different dopant species into the van-der-Waals gaps between the Cl-separated Ti-O double layers. Indeed, XPS shows that the Ti valency is reduced through charge transfer from the dopant. While the new spectral weight in the charge gap, as observed by ARPES, nicely follows the expected behaviour for the correlated bands of a Mott insulator, no quasiparticle peak can be found at the chemical potential. The seeming abscence of a metallic QP can be reconciled in a picture where its coherent weight is transferred to higher binding energies due to coupling to polaronic or other degrees of freedom.