The quasi-one-dimensional Chevrel phases, $A_2{\mathrm{Mo}}_6{\mathrm{Se}}_6$ ($A=\mathrm{Tl}$, In, K, Rb, Cs), are of interest due to their atypical electronic properties. The Tl and In analogs undergo a superconducting transition whereas the alkali metal analogs show charge gapping of another, not well understood type. We report the results of inelastic neutron scattering on polycrystalline ${\mathrm{In}}_2{\mathrm{Mo}}_6{\mathrm{Se}}_6$ ($T_{\mathrm{c}}=2.85$ K) and ${\mathrm{Rb}}_2{\mathrm{Mo}}_6{\mathrm{Se}}_6$ (nonsuperconducting) samples, which reveal a column of intensity with linear dispersion from [0 0 1/2] to [0 0 1] in both compounds. The observed temperature and $\left|Q\right|$ independence together suggest the presence of unconventional carriers with a spin contribution to the excitation. This is contrary to the prevailing model for these materials, which is that they are nonmagnetic. The excitation has similar dispersion and $S\left(Q,\mathrm{E},T\right)$ behavior as one observed in the structurally related superconducting compounds $A_2{\mathrm{Cr}}_3{\mathrm{As}}_3$ and $A_2{\mathrm{Mo}}_3{\mathrm{As}}_3$ ($A=\mathrm{K}$, Rb, Cs), which has been interpreted as magnetic in origin and related to Fermi surface nesting. The connection is unexpected because the calculated Fermi surface of the arsenides differs substantially from the $A_2{\mathrm{Mo}}_6{\mathrm{Se}}_6$ compounds, and many consider them distinct classes of materials. This observation suggests a hidden link in the physics between both classes of superconductors, perhaps originating from their quasi-low-dimensional character.

• Received 19 November 2021
• Accepted 18 October 2022

DOI:https://doi.org/10.1103/PhysRevMaterials.6.124804