Static and dynamic properties of low-temperature order in the one-dimensional semiconductor (NbSe_4)_3I

摘要

We investigated static and dynamic lattice properties in a quasi-one-dimensional charge-ordered semiconductor (NbSe_4)_3I 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~* ≈ 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.