Regensburg 2016 – scientific programme

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O: Fachverband Oberflächenphysik

O 35: Ultrafast Phenomena I

O 35.8: Invited Talk

Tuesday, March 8, 2016, 11:45–12:15, H10

Coherent Quantum Dynamics of Excitons in Atomically Thin Semiconductors — •xiaoqin li — Univ. of Texas-Austin, Austin, USA

The transitional metal dichalcogenides (TMDs) are an emerging class of atomically thin semiconductors with tightly-bound excitons and charged excitons (i.e. trions). A fundamental property of these quasiparticles is quantum decoherence time, which reflects irreversible quantum dissipation arising from system (excitons) and bath (vacuum and other quasiparticles) interaction and determines the timescale during which excitons can be coherently manipulated. Dephasing time is also equivalent to the intrinsic homogeneous linewidth of exciton resonances. In addition, excitons in TMDs are localized at the corners of the Brillouin zone and provide a convenient way to optically manipulate the valley degree of freedom. Direct measurement of valley coherence time is challenging because it corresponds to non-radiative coherence between two degenerate states. Using ultrafast multi-dimensional optical spectroscopy, we investigate the intrinsic homogeneous linewidth of excitons, exciton valley coherence as well as coupling between excitons and trions. Our studies reveal coherent exciton dynamics on the order of ~ 100 fs in monolayer TMDs. Decoherence time is not only an important parameter for characterizing fundamental properties of excitons, but also serves as a sensitive probe for exciton-exciton and exciton-phonon interaction.