MoWSe_Spin and pseudospin properties of energetically controllable dark and bright excitons in tailored Mo1-xWxSe2 alloys

• Applicant: Dr. Jörg Debus
• Subject Area: Experimental Condensed Matter Physics
• Term: from 2017 to 2021
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 382264508

Two-dimensional transition metal dichalcogenides, whose layered structure allows for unusually strongly bound excitons existing even at room temperature, possess unique spin and valley pseudospin features that may give rise to highly exciting and novel physics for the nanophotonics as well as spin-based nanoelectronics. In order to exploit the full potential of this new material system and to allow one to tailor the functional and structural properties of these nanomaterials, key open questions regarding the excitons in their monolayers have to be answered.For that purpose, we focus on the interaction between optically bright and dark K-valley excitons in novel Mo1-xWxSe2 alloys. The composition dependence of these mechanically exfoliated alloys shall allow us to tune the energies of the A- and B-exciton spin states, also leading to a dark- and bright-exciton mixing, in a wide range. Using the Mo1-xWxSe2 structures with tunable conduction- and valence-band levels, we expect to provide novel and thorough insights into the spin and valley pseudospin properties and dynamics, which shall be studied with regard to the tunable exciton and carrier exchange interactions and spin-orbit coupling as well as to the interaction of the excitons with the surrounding bath. The latter shall include not only nuclear spins and phonons, but also defects, substrate materials and the monolayer geometry. Optically detected magnetic resonance techniques combined with resonant and polarized laser excitation and micrometer spatial resolution shall allow for a magnetic resonance imaging of the spin-based exciton properties, thus making a step toward spin-based quantum information devices and sensor technologies. Besides the composition-dependent controllability of the dark and bright exciton energies, we will apply uni- and biaxial strain to the substrate material for fine-tuning the spin state energies, manipulating the spin-orbit coupling of the electrons and particularly holes and changing symmetry conditions. A comparative study of the K- and Gamma-valley excitons shall furthermore enhance the understanding of spin and many-carrier physics, by exploiting high-energy laser excitation with variable power, in the tailored Mo1-xWxSe2 structures.

• DFG Programme: Research Grants
• International Connection: Poland
• Partner Organisation: Narodowe Centrum Nauki (NCN)
• Co-Investigator: Professor Dr. Manfred Bayer
• Cooperation Partners: Professor Dr. Leszek Bryja, Ph.D.; Dr. Joanna Jadczak