1T-TiSe₂ is a transition-metal dichalcogenide semimetal that is the subject of the 2020 Nature paper "Spontaneous gyrotropic electronic order in a transition-metal dichalcogenide" by Su-Yang Xu et al. (Nature 578, 545–549, doi:10.1038/s41586-020-2011-8, Epub 26 February 2020). The source digest reproduces the abstract and links a companion CHESS write-up by Elke Arenholz.
Reported result
The material has a non-chiral crystal structure, yet a team led by Nuh Gedik's group at mit demonstrated spontaneous chiral symmetry breaking by electrons in it. Shining mid-infrared circularly polarized light on 1T-TiSe₂ while cooling it below the critical temperature leads to the preferential formation of one chiral domain. The chirality of this state is confirmed by measurement of an out-of-plane Circular Photogalvanic Effect current whose direction depends on the optical induction.
Significance
The result is presented as the realization of optical chiral induction and the observation of a gyrotropically ordered phase — a state in which electrons spontaneously organize to exhibit macroscopic chirality in an originally achiral lattice, proposed as the quantum analogue of cholesteric liquid crystals. The abstract notes that although the role of domain walls requires further investigation with local probes, the methodology can be applied to realize and control chiral electronic phases in other quantum materials.
Source notes & attribution
- https://rexresearch.com/CISSMetamaterial/CISSMetamaterial.html