In the s = 1/2 antiferromagnetic spin chain material TiPO4 the formation of a spin gap takes place in a two step process with two characteristic temperatures, T*=111 K and TSP=74 K. We observe an unusual lattice dynamics over a large temperature regime as well as evidence for an orbital instability preceding the spin-Peierls transition. We relate different intrachain exchange interactions of the high temperature compared to the spin-Peierls phase to a modification of the orbital ordering pattern. In particular, our observation of a high energy excitation of mixed electronic and lattice origin suggests an exotic dimerization process different from other spin-Peierls materials.
@article{arxiv.1311.6538,
title = {Lattice and orbital fluctuations in TiPO4},
author = {Dirk Wulferding and Angela Möller and Kwang-Yong Choi and Yurii G. Pashkevich and Roman Yu. Babkin and Karina V. Lamonova and Peter Lemmens and Joseph M. Law and Reinhard K. Kremer and Robert Glaum},
journal= {arXiv preprint arXiv:1311.6538},
year = {2013}
}