Electronic structure of the spin-12quantum magnet TiOCl

We have studied the electronic structure of the spin-$1∕2$ quantum magnet TiOCl by polarization-dependent momentum-resolved photoelectron spectroscopy. From that, we confirm the quasi-one-dimensional nature of the electronic structure along the crystallographic $b$ axis and find no evidence for sizable phonon-induced orbital fluctuations as the origin for the noncanonical phenomenology of the spin-Peierls transition in this compound. A comparison of the experimental data to our own $\mathrm{LDA}+\mathrm{U}$ and Hubbard model calculations reveals a striking lack of understanding regarding the quasi-one-dimensional electron dispersions in the normal state of this compound.