Twisting Light: New Metasurfaces Unlock Room-Temperature Valleytronics

Transition metal dichalcogenides (TMDs) such as MoSe2 possess a unique property called 'valley pseudospin', which allows for the coupling of photon and electron spin—a promising avenue for next-generation information processing known as valleytronics. However, a significant barrier has been 'valley-dephasing', a process where these delicate states break down rapidly, typically preventing high-performance operation at room temperature.

In a major breakthrough, scientists have demonstrated that a chiral resonant metasurface can enable valley-selective emission in MoSe2 monolayers at room temperature. A metasurface is an engineered material with properties not found in nature; in this case, it is designed to be chiral, meaning it has a distinct structural 'handedness'. This platform provides circular eigen-polarisation states with a high quality factor (Q-factor) of up to 450, significantly boosting the interaction between light and matter.

The results are groundbreaking for the field. The study reveals a degree of circular polarisation (DOP) reaching a record high of 0.5 at room temperature, independent of the excitation polarisation. Measurements indicate this stability is due to a significantly increased 'chiroptical local density of states', which enhances valley-specific radiative transition rates by a factor of approximately 13. This work effectively bypasses the rapid dephasing issues of the past, paving the way for the development of ultracompact chiral classical and quantum light sources.