Group Seminar via Zoom: Polarisation- and coupling effects of two-dimensional transition metal dichalcogenides (TMDCs) in the strong coupling regime at room temperature
Christoph Rupprecht, Uni Würzburg
Group meeting via video conference (Zoom)
Tuesday, December 1st, 9:00 (MEZ)
Dealing with the unique situation of partial lock downs worldwide and home office solutions at our Institute due to the current spreading of the Covid 19 virus, we are now holding our group seminars and journal clubs via video conference. This procedure enables us to continue our research, enhance discussions and exchange important information.
Atomically thin transition metal dichalcogenide crystals (TMDCs) belong to an emergent class of materials relevant to studies in fundamental- as well as application-oriented light matter interaction. They combine huge oscillator strength (optical activity) and giant exciton binding energies, making them a particularly interesting platform for cavity quantum electrodynamics. To date, the regime of strong light matter coupling in optical microcavities has been convincingly demonstrated with single monolayers, even at room temperature. First, I will discuss the influence of real and artificial magnetic fields in the strong coupling regime. Precisely, the application of external magnetic fields lifts the energetic degeneracy of 𝜎𝜎+ and 𝜎𝜎_ polarized valley excitons via the Zeeman-effect, what we could demonstrate recently at room temperature . While the position of the polariton’s polarization vector follows the polarization vector in the absence of a magnetic field (valley coherence), the lifting of the valley degeneracy by a magnetic field leads to a precession of the polaritons’ polarization vector, and a rotation of the polarization vector by up to 90°. This polarization angle can also be rotated by the angle-dependent linear polarization splitting acting as a artificial magnetic field by up to 280°.  Further, I show, that locally changing the number of layers in a WSe2/hBN/WSe2 van-der-Waals heterostructure embedded in a monolithic, high-quality-factor cavity gives rise to a local variation of the coupling strength. This effect yields a polaritonic stair case potential, which we demonstrated at room temperature . As conclusion, I will discuss first steps to trap TMDC exciton-polaritons in photonic lattices.
 C. Rupprecht, E. Sedov, M. Klaas, H. Knopf, M. Blei, N. Lundt, S. Tongay, T. Taniguchi, K. Watanabe, U. Schulz, A. Kavokin, F. Eilenberger, S. Höfling, and C. Schneider, "Manipulation of room- temperature valley-coherent exciton-polaritons in atomically thin crystals by real and artificial magnetic fields," 2D Mater. 7(3), (2020).
 C. Rupprecht, M. Klaas, H. Knopf, T. Taniguchi, K. Watanabe, Y. Qin, S. Tongay, S. Schröder, F. Eilenberger, S. Höfling, and C. Schneider, "Demonstration of a polariton step potential by local variation of light-matter coupling in a van-der-Waals heterostructure," Opt. Express 28(13), 18649 (2020).
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