Ultrafast spectroscopy of multilayer transition-metal dichalcogenides

• Applicant: Professor Dr. Christian Schüller
• Subject Area: Experimental Condensed Matter Physics
• Term: since 2024
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 544403076

In this project, the spin-, valley-, and pseudospin dynamics in MoSe2 and WSe2 multilayers shall be explored in external electric and magnetic fields. The project is based on our recent, intriguing finding of pseudospin quantum beats in MoSe2 and WSe2 multilayers, which revealed a rather unexpected nonzero in-plane g factor of these materials [Rai22]. Time-resolved Faraday ellipticity, transient differential transmission, and time-resolved photoluminescence experiments will be employed to research the origin of these quantum oscillations in depth. We will compare time-resolved optical experiments in in-plane magnetic fields on both, R-type and H-type stacked multilayers with different layer numbers N, starting with N = 2 to highlight the origin of the observed quantum beats to be of intralayer- or interlayer type. Via comparison of transient differential transmission and time-resolved photoluminescence on the same samples we will answer the question whether or not ultrafast scattering of electrons from the K to the sigma valley of the multilayers plays a role in our experiments. Following from this, we will conclude if we see in the experiments quantum beats of excitons or of only their hole part at the K valleys. Furthermore, we hypothesize that the magnitude of the nonzero in-plane g factor of multilayers is caused by hybridization of intralayer excitons with interlayer- and maybe also every-other-layer ones. Therefore, we will investigate systematically multilayers, starting with N = 2, since every-other-layer excitons are possible, starting from N = 3, only. The Stark shift, caused by an out-of-plane electric field will be employed to enhance the valley lifetime of excitons and to tune the hybridization of intralayer- and every-other-layer excitons to investigate their influence on the g factor and on the pseudospin quantum beats.

• DFG Programme: Research Grants