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arXiv · 1710.09739

Valley-selective optical Stark effect probed by Kerr rotation

Trevor LaMountain·Hadallia Bergeron·Itamar Balla·Teodor K. Stanev·Mark C. Hersam·Nathaniel P. Stern
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Abstract

The ability to monitor and control distinct states is at the heart of emerging quantum technologies. The valley pseudospin in transition metal dichalcogenide (TMDC) monolayers is a promising degree of freedom for such control, with the optical Stark effect allowing for valley-selective manipulation of energy levels in WS$_2$ and WSe$_2$ using ultrafast optical pulses. Despite these advances, understanding of valley-sensitive optical Stark shifts in TMDCs has been limited by reflectance-based detection methods where the signal is small and prone to background effects. More sensitive polarization-based spectroscopy is required to better probe ultrafast Stark shifts for all-optical manipulation of valley energy levels. Here, we show time-resolved Kerr rotation to be a more sensitive probe of the valley-selective optical Stark effect in monolayer TMDCs. Compared to the established time-resolved reflectance methods, Kerr rotation is less sensitive to background effects. Kerr rotation provides a five-fold improvement in the signal-to-noise ratio of the Stark effect optical signal and a more precise estimate of the energy shift. This increased sensitivity allows for observation of an optical Stark shift in monolayer MoS$_2$ that exhibits both valley- and energy-selectivity, demonstrating the promise of this method for investigating this effect in other layered materials and heterostructures.

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Trevor LaMountain, Hadallia Bergeron, Itamar Balla, Teodor K. Stanev, Mark C. Hersam, Nathaniel P. Stern. 2017-10-26. Valley-selective optical Stark effect probed by Kerr rotation. https://doi.org/10.1103/physrevb.97.045307

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