Rostock 2019 – scientific programme

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MO: Fachverband Molekülphysik

MO 21: Coupled Systems

MO 21.6: Talk

Thursday, March 14, 2019, 15:30–15:45, S HS 001 Biologie

Broadband Time-Resolved Circular Dichroism Spectroscopy of Monolayer MoS₂ — •Heiko Hildenbrand¹, Andreas Steinbacher¹, Hope Bretscher², Akshay Rao², and Tobias Brixner¹ — ¹Institut für Physikalische und Theoretische Chemie, Universität Würzburg, Am Hubland, 97074 Würzburg — ²Department of Physics, Cavendish Laboratory, University of Cambridge, 19 JJ Thompson Avenue, Cambridge, CB3 0HE, UK

Circular dichroism (CD) is a common technique for analyzing chiral samples by their difference in absorption of left and right circularly polarized light. Here we present broadband time-resolved CD spectroscopy which is based on the pump–probe technique paired with a setup capable of mirroring an arbitrary polarization state of an ultrashort laser pulse [1]. Hence, by passing a circularly polarized broadband probe pulse through this setup, we can switch between opposite handedness on a shot-to-shot basis. In combination with a chopping scheme, this allows us to simultaneously acquire data of transient CD and absorption changes.

To demonstrate the capabilities of this approach we selectively excite the K and K’ valley of a MoS₂ monolayer on a quartz substrate with circularly polarized femtosecond pulses. Since the valley degree of freedom is only accessible via helicity-sensitive techniques, we investigate the ultrafast valley dynamics by time-resolved CD spectroscopy and complement the results with information obtained via transient absorption spectroscopy of the A and B excitonic bands.

[1] Steinbacher et al., Opt. Express 25, 21736 (2017)