Fe1+yTe with y≲0.05 exhibits a first-order phase transition on cooling to a state with a lowered structural symmetry, bicollinear antiferromagnetic order, and metallic conductivity, dρ/dT>0. Here, we study samples with y=0.09(1), where the frustration effects of the interstitial Fe decouple different orders, leading to a sequence of transitions. While the lattice distortion is closely followed by \emph{incommensurate} magnetic order, the development of \emph{bicollinear} order and metallic electronic coherence is uniquely associated with a separate hysteretic first-order transition, at a markedly lower temperature, to a phase with dramatically enhanced bond-order wave (BOW) order. The BOW state suggests ferro-orbital ordering, where electronic delocalization in ferromagnetic zigzag chains decreases local spin and results in metallic transport.
@article{arxiv.1307.7162,
title = {Ferro-orbital ordering transition in iron telluride Fe$_{1+y}$Te},
author = {David Fobes and Igor A. Zaliznyak and Zhijun Xu and Ruidan Zhong and Genda Gu and John M. Tranquada and Leland Harriger and Deepak Singh and V. Ovidiu Garlea and Mark Lumsden and Barry Winn},
journal= {arXiv preprint arXiv:1307.7162},
year = {2018}
}