Comment on "Chiral Phase Transition in Charge Ordered 1T-TiSe2" and Supplementary Material on "First-order Forbidden X-ray Diffraction"

TL;DR

This paper refutes previous claims of a chiral phase transition in TiSe2 based on x-ray diffraction data, demonstrating that there is only one achiral transition instead of multiple transitions.

Contribution

It critically reanalyzes prior x-ray diffraction evidence, showing that the supposed chiral transition in TiSe2 does not exist, clarifying the nature of its phase transition.

Findings

Prior evidence for chiral transition is incorrect

There is only one achiral phase transition in TiSe2

Previous modeling assumptions are invalid

Abstract

A prior report of the emergence of chirality for the (2x2x2) charge density wave (CDW) in TiSe2 has attracted much interest; the drastic symmetry breaking is highly unusual with few precedents [1]. In that study, key evidence was provided by x-ray diffraction measurements of two superlattice reflections, (1.5 1.5 0.5) and (2.5 1 0). The (2.5 1 0) reflection appeared to show an anomalously large intensity and a transition onset at ~7 K below that of the (1.5 1.5 0.5) reflection. These observations, aided by modeling, were cited as evidence for a separate chiral transition. In this Comment, we show that the prior conclusions based on x-ray diffraction are erroneous. There is just one transition, and it is achiral.