"Forbidden" phonon: dynamical signature of bond symmetry breaking in the iron chalcogenides

Abstract

Investigation of the inelastic neutron scattering spectra in Fe${}_{1+y}$Te${}_{1-x}$Se${}_x$ near a signature wave vector $\mathbf{Q}=(1,0,0)$ for the bond-order wave (BOW) formation of parent compound Fe${}_{1+y}$Te [Phys. Rev. Lett. 112, 187202 (2014)] reveals an acoustic-phonon-like dispersion present in all structural phases. While a structural Bragg peak accompanies the mode in the low-temperature phase of Fe${}_{1+y}$Te, it is absent in the high-temperature tetragonal phase, where Bragg scattering at this $\mathbf{Q}$ is forbidden by symmetry. Notably, this mode is also observed in superconducting FeTe${}_{0.55}$Se${}_{0.45}$, where structural and magnetic transitions are suppressed, and no BOW has been observed. The presence of this "forbidden" phonon indicates that the lattice symmetry is dynamically or locally broken by magneto-orbital BOW fluctuations, which are strongly coupled to lattice in these materials.

5 pages, 4 figures; supplement: 8 pages, 9 figures

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Cited by in corpus (5)

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• Empty perovskites as Coulomb floppy networks: entropic elasticity and negative thermal expansion
• Neutron Scattering Signature of Phonon Renormalization in Nickel (II) Oxide
• Unexpected Enhancement of Three-Dimensional Low-Energy Spin Correlations in Quasi-Two-Dimensional Fe${}_{1+y}$Te${}_{1-x}$Se${}_x$ System at High Temperature