Periodic Reporting for period 1 - IMME-NEM (Imaging the Motion of Magneto-Excitons in New Emerging Materials)
Período documentado: 2017-10-01 hasta 2019-09-30
The main purpose of this research project was to provide a fundamental understanding of valley-exciton dispersion and, resulting transport, combining two main research objectives: (R1) to determine the exciton dispersion and the corresponding transport using momentum- and real-space imaging, and (R2) to achieve an external control of the exciton dispersion via applied magnetic fields.
Research objective R2 was addressed in the WP2, consisting of four tasks investigating the control of valley exciton dispersion using high magnetic fields. Tasks 2.1 and 2.2 was to ‘Design and build of the imaging system for dc magnetic fields’ and ‘Test the imaging system’. These tasks were achieved by re-developing and extending the setup designed in WP1 for the use in dc magnetic fields. Task 2.3 was to manipulate the exciton dispersion and transport via applied magnetic fields. Several experiments were performed on neutral and charged exciton (trion) in single-layers TMDs samples. Two main effects of magnetic field on the photoluminescence (PL) profiles of excitons were observed: (i) the extent of both exciton and trion PL emission decreases with increasing field and, (ii) the halo-like shape of the trion emission PL profiles vanishes in field. Task 2.4 was to analyse the data and write publications. The data has been analysed and the results are summarized in a paper that is now in preparation.
Main Results:
• First development of polarization-resolved optical imaging setup able to take both real- and momentum-space images at low temperatures in high fields of excitons in single-layer TMDs.
• First successful tests of optical imaging setup. The equipment can be used for other material systems as well, such as exciton-polaritons in semiconductor microcavities, black phosphorous, van der Waals heterostructures, and other semiconductor nanostructures.
• First measurements of intra- and inter-layer exciton diffusion in high fields up to 30T.
• Systematic characterization of exciton diffusion at different temperatures and excitation conditions (laser energy, polarization).
• Analysis of neutral and charged exciton photoluminescence profiles evolution as a function of increased perpendicular magnetic field.
• First observation of exciton bright exciton splitting in strained single layer TMDs.
• Observation of anomalous rotation of the linearly polarized emission of bright excitons in strained single layer TMDs under high magnetic fields.
• Observation of magneto-optical alignment of localized excitons in single-layer TMDs quantum dots.
• Observation of chiral exciton-phonon coupling in strained single-layer TMDs.
This project has helped to determine the exciton dispersion and the corresponding transport in atomically flat single-layers of transition-metal dichalcogenides. In addition, the project has helped to better understand the effect of (uniaxial) strain on exciton properties (the splitting in the spectral lines of the exciton emission, the modification in both the linear and circular polarization properties, caused by a strong mixing between the exciton levels, the variation of g-factors in an applied magnetic field), and on valley coherence.
Impact of Projected Results:
The IMME-NEM project proved to significantly advance our fundamental understanding of valley-exciton dispersion and resulting transport in two-dimensional single-layer transition-metal dichalcogenides, and therefore it advances our understanding of Dirac materials. It provides a wealth of experimental data for the understanding of many-body physics.
It is expected that the project will have a great impact on the research community, as well as on existing and new users of HFML-Nijmegen. The unique combination of optical imaging with high magnetic field opens access to international scientists working on other material systems, such as exciton-polaritons in semiconductor microcavities, black phosphorous, and other semiconductor nanostructures. Furthermore, it offered the possibility to gain fundamental knowledge about the peculiar properties of excitonic particles in 2D TMDs and deepen my understanding of the emerging phenomena crucial for the use of excitons in new photonic and/or valleytronic devices.