${\mathrm{Fe}}_{1+y}\mathrm{Te}$ with $y\lesssim 0.05$ exhibits a first-order phase transition on cooling to a state with a lowered structural symmetry, bicollinear antiferromagnetic order, and metallic conductivity, $d\rho /dT>0$. 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 incommensurate magnetic order, the development of 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.

• Received 26 July 2013

DOI:https://doi.org/10.1103/PhysRevLett.112.187202