Static and dynamic properties of low-temperature order in the one-dimensional semiconductor(NbSe4)3I

We investigated static and dynamic lattice properties in a quasi-one-dimensional charge-ordered semiconductor ${({\mathrm{NbSe}}₄)}₃\mathrm{I}$ by using Raman, femtosecond pump-probe spectroscopy and x-ray diffraction. In addition to a well-documented pseudo-Jahn-Teller ferrodistortive structural transition at ${T}_C=274$ K, where the displacements of Nb ions lead to ferroelectric (FE) in-chain polarization with opposite direction in adjacent chains, all methods suggest an additional lowering of symmetry at ${T}^*\ensuremath{\approx}160$ K. Although antiferroelectric (AFE) phase is partially formed at ${T}_C$, our results consistently point to an enhancement of the interchain order at ${T}^*$, thus leading to AFE order-disorder transition, as supported by the earlier dielectric and structural studies.