The circular photogalvanic effect is a change in photocurrent that is measured when the helicity of light is flipped. As described in the CHESS write-up reproduced by the source digest, such a change can only occur if the electrons in the material are chiral. It therefore serves as a measurement technique for detecting chiral electronic order.
Use in detecting gyrotropic order
The technique was employed by a team led by Nuh Gedik's group at mit to demonstrate spontaneous chiral symmetry breaking by electrons in 1T-TiSe₂, despite that material's non-chiral crystal structure. In the 2020 Nature paper by Su-Yang Xu et al., the chirality of the optically induced state was confirmed by measurement of an out-of-plane circular photogalvanic current whose direction depends on the optical induction.
Context
The measurement is one of the experimental handles on Gyrotropy in condensed matter, alongside the electrical magnetochiral effect used in the 2025 MoS₂ work on voltage-controlled interfacial chirality. Both techniques detect chirality through transport signatures rather than through structural probes.
Source notes & attribution
- https://rexresearch.com/CISSMetamaterial/CISSMetamaterial.html