News from Nanotechjapan

物性・原理

Transfer of polarization information loaded on an exciton as future information media---First observation of Exciton Hall effect in monolayer MoS2---

 The University of Tokyo issued a press release on 3rd October 2017 that a collaborative research group from the university and Osaka University has succeeded in observing a Hall effect of excitons in monolayer MoS2 and polarization-selective spatial transport of excitons on a micrometer scale. The results were published in Nature Materials * with Professor Yoshihiro Iwasa as the senior author.

 Excitons are composite particles of electrons and holes combined by Coulomb force in semiconductors. Light absorption creates excitons, and excitons move around inside solids. Two kinds of excitons are created having the same energy, but different polarization. The research group directly observed the exciton transportation in monolayer MoS2 by polarization-resolved photoluminescence mapping. They found that excitons created by photons with right circular polarization move in a different direction from those created by photons with left circular polarization. The experimental results show spontaneous Hall effect under an internal magnetic flux, and can be used to control the information flow, such as spin and momentum.

 The result offers a route to explore exciton-based "valleytronics" (freedom in momentum in crystal utilized instead of spin in spintronics) in two-dimensional materials.

* Masaru Onga, Yijin Zhang, Toshiya Ideue & Yoshihiro Iwasa,  "Exciton Hall effect in monolayer MoS2", Nature Materials (2017) doi:10.1038/nmat4996; Published online 02 October 2017