S=12chains and spin-Peierls transition in TiOCl

Abstract

We study TiOCl as an example of an $S=\frac{1}{2}$ layered Mott insulator. From our analysis of susceptibility data, combined with local-density-approximation (LDA) and $\mathrm{LDA}+U$ band-structure calculations, we conclude that orbital ordering produces quasi-one-dimensional spin chains and that TiOCl is an example of Heisenberg chains that undergo a spin-Peierls transition. The energy scale is an order of magnitude larger than that of previously known examples. The effects of nonmagnetic Sc impurities are explained using a model of broken finite chains.