Spin-polarized cathodoluminescence in 2D materials and van der Waals heterostructures – SpinCat

Preliminary polarized micro-photoluminescence experiments has been done in encapsulated single layer WS2 prepared in out lab. The small linewidth of excitonic transitions confirms the excellent optical quality of the samples. Promising results concerning novel spin related phenomena have been observed. These measurements are currently being completed with time-resolved photoluminescence performed in the Quantum optoelectronics group (LPCNO Toulouse). These results are expected to be published by late 2020.

Sample fabrication: The SpinCAT project needs, in a first time, the development of a state of the art exfoliation setup in order to prepare good quality samples. This setup has been installed in 2019 and has allowed our group to obtain single layers of MX2 (M=Mo,W ; X=S,Se, Te) of excellent optical quality, as attested by their photoluminescence spectra at cryogenic temperatures (see Figure 1). In addition, an annealing chamber has been built in order to improve the homogeneity of the prepared flakes. Finally, the team has recently bought a glovebox in order to prepare the samples in a controlled atmosphere. We expect the glovebox to be delivered before November 2020.

The samples are of excellent quality and compared to the state of the art found in the literature. This is a key step towards the success of this project.

The next step consists in studying the cathodoluminescence of 2D materials, firstly by using a scanning tunneling luminescence microscope, and in a second step by directly using a spin polarized electron beam. Samples have already been fabricated, consisting in monolayers exfoliated onto ITO, which is a transparent yet conductive substrate, perfectly adapted to this kind of measurements.

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The roadmap of future innovative device developments foresees the reduction of material dimensions down to nanometer scale and
the incorporation of 2D compounds with novel degrees of freedom (DOF). For instance 2D semiconductors like MoS2 monolayers
exhibit a spin texture of the band structure due to a unique coupling between the spin and valley (momentum) DOF. The "SpinCAT" project aims to
explore this unique spin-valley coupling by original and versatile experimental techniques able to explore the valley dynamics and the electronic
structure of a wide variety of materials, including 2D semiconductors and their heterostructures of potential use in future
applications. The proposed approach is based on the development of a state of the art spin-polarized cathodoluminescence
spectroscopy setup complemented by scanning tunneling luminescence.
This project will benefit from very recent developments in sample fabrication and a rich scientific environment which favours
interactions with theoreticians and experts in condensed matter physics