Determine whether the normal-state infrared phonon is intrinsically split

Determine whether the normal-state infrared phonon peak of 1T-TiSe₂ consists of two modes with a small splitting that is obscured by fluctuating charge order and the resulting increased linewidth above the charge-density-wave transition.

Background

The paper observes that the doubly degenerate E_u infrared phonon splits into two resolvable modes at the charge-density-wave transition, while the corresponding normal-state peak above the transition is broader. The authors argue that fluctuating charge order could broaden two already split modes sufficiently to make them appear as a single peak. Using the observed linewidth and a resolution criterion, they find that the modes would not be experimentally resolved just above the transition, leaving open whether the high-temperature peak is genuinely a single mode or an unresolved pair.

References

We therefore cannot exclude that the normal-state phonon peak consists of two split modes.

— Infrared evidence for strong $C_{3}$ symmetry breaking in 1$T$-TiSe$_{2}$  (2609.24705 - Grondelle et al., 21 Sep 2026) in Discussion and Summary, paragraph beginning “We conclude by discussing the possible persistence of CDW fluctuations above T_CD W”