The chiral phase transition in charge ordered 1T-TiSe2

TL;DR

This paper provides experimental evidence for a sequence of phase transitions in 1T-TiSe2, revealing a transition from disordered to non-chiral, and finally to chiral charge order, confirming theoretical predictions about its chiral phase behavior.

Contribution

It experimentally confirms the predicted hierarchy of charge ordered phases, including a novel chiral phase transition in 1T-TiSe2.

Findings

Identification of a phase transition ~7 K below the main charge order transition.

Observation of a transition from non-chiral to chiral charge order.

Experimental validation of the theoretical model predicting chirality emergence.

Abstract

It was recently discovered that the low temperature, charge ordered phase of 1T-TiSe2 has a chiral character. This unexpected chirality in a system described by a scalar order parameter could be explained in a model where the emergence of relative phase shifts between three charge density wave components breaks the inversion symmetry of the lattice. Here, we present experimental evidence for the sequence of phase transitions predicted by that theory, going from disorder to non-chiral and finally to chiral charge order. Employing X-ray diffraction, specific heat, and electrical transport measurements, we find that a novel phase transition occurs ~7 K below the main charge ordering transition in TiSe2, in agreement with the predicted hierarchy of charge ordered phases.