Wydarzenia

Seminarium Fizyki Politechniki Wrocławskiej

Enhancing the magnetooptical response of two-dimensional semiconductors

dr inż. Tomasz Woźniak

Institute of Theoretical Physics, Faculty of Fundamental Problems of Technology Wrocław University of Science and Technology

Monolayers of semiconducting transition metal dichalcogenides (TMDCs) emit light very efficiently and display rich spin-valley physics, with excitonic g-factors of about −4. Vertical heterostructures based on TMDCs can host excitonic complexes with much larger g-factors, that can be tuned by interlayer twist angle and stacking registry. These parameters are, however, not easy to control during preparation of the samples. Recently, we have shown by magnetooptical spectroscopy and density functional theory (DFT) calculations that mixed (Mo,W)Se2 monolayers at certain compositions exhibit significantly larger exciton g-factors than the parent crystals. We quantitatively identify the alloy-induced mixing between different conduction band valleys as the underlying mechanism originating the anomalous composition dependence of the neutral exciton g-factor. The theoretical framework also suggests a high strain sensitivity of the alloys, making them promising candidates for tailor-made optoelectronic devices. [1]

We have also studied theoretically the optoelectronic properties of selected MA2Z4 monolayers that form a new class of hexagonal 2D materials, isosymmetric to TMDCs. From DFT and effective Bethe–Salpeter-equation-based calculations we predict high exciton binding energies, effective g-factors and diamagnetic coefficients. In particular, large positive g-factors are predicted for excitons involving higher conduction bands. [2]