Abstract
The main aspects of physical phenomena associated with the optical orientation of the spin and valley degrees of freedom in transition metal dichalcogenide monolayers and in van der Waals heterostructures based on them have been briefly reviewed. Owing to features of the band structure and spin–orbit coupling in such systems, circularly polarized light induces optical transitions in different valleys K+ and K– of the Brillouin zone; consequently, the optical orientation of charge carriers and excitons is accompanied by their valley polarization. The main features of the band structure of transition metal dichalcogenide monolayers, excitonic effects, and results of theoretical studies of the valley orientation of excitons and electrons at one-photon absorption have been reported. The linear–circular dichroism and valley orientation of free charge carriers and excitons at multiphoton absorption have been studied. Effects associated with the trigonal symmetry of monolayers, including the inversion of valley polarization at two-photon transitions and the second harmonic generation, have been discussed. The considered theoretical models have been illustrated by experimental data.
Highlights
The investigation of processes of optical orientation of spins of charge carriers, spin dynamics, and manifestation of spin polarization in the optical response of semiconductors and semiconductor nanosystems has become an actively developing field of modern physics [1,2,3,4]
Structures with “extreme” two-dimensionality such as graphene, transition metal dichalcogenide (TMDC) monolayers, hexagonal boron nitride monolayers, and van der Waals heterostructures based on them have become of particular interest in the last several years in the physics of semiconductor nanosystems [5, 6]
In TMDC monolayers [7,8,9,10], among which MoS2, MoSe2, WS2, and WSe2 are the most studied and which are considered in this brief review, a direct band gap is formed at the points K+ and K– at the edges of the hexagonal Brillouin zone because of the strong spin–orbit coupling and a specific symmetry of the crystal lattice
Summary
The investigation of processes of optical orientation of spins of charge carriers, spin dynamics, and manifestation of spin polarization in the optical response of semiconductors and semiconductor nanosystems has become an actively developing field of modern physics [1,2,3,4]. Light with a given circular polarization σ+ or σ− in the dipole approximation is absorbed in the K+ or K− valley, respectively, and the spin orientation of charge carriers is accompanied by their valley orientation [9, 11,12,13,14,15,16] Another feature of TMDC monolayers is a strong Coulomb interaction, which is responsible for the connection of the optical response of such structure with Wannier–Mott excitons having a significant binding energy of 100– 500 meV [17,18,19,20].
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
