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arXiv · 2006.02640

Enhanced exciton-exciton collisions in an ultra-flat monolayer MoSe2 prepared through deterministic flattening

T. Hotta·A. Ueda·S. Higuchi·M. Okada·T. Shimizu·T. Kubo·K. Ueno·T. Taniguchi·K. Watanabe·R. Kitaura
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Abstract

Squeezing bubbles and impurities out of interlayer spaces by applying force through a few-layer graphene capping layer leads to van der Waals heterostructures with ultra-flat structure free from random electrostatic potential arising from charged impurities. Without the graphene capping layer, a squeezing process with an AFM tip induces applied-force-dependent charges of n ~ 2 x 10^12 cm^-2 uN^-1, resulting in strong intensity of trions in photoluminescence spectra of MoSe2 at low temperature. We found that a hBN/MoSe2/hBN prepared with the "modified nano-squeezing method" shows a strong excitonic emission with negligible trion peak, and the residual linewidth of the exciton peak is only 2.2 meV, which is comparable to the homogeneous limit. Furthermore, in this high-quality sample, we found that formation of biexciton occurs even at extremely low excitation power (Phi ~ 2.3 x 10^19 cm^-2 s^-1) due to the enhanced collisions between excitons.

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T. Hotta, A. Ueda, S. Higuchi, M. Okada, T. Shimizu, T. Kubo, K. Ueno, T. Taniguchi, K. Watanabe, R. Kitaura. 2020-06-04. Enhanced exciton-exciton collisions in an ultra-flat monolayer MoSe2 prepared through deterministic flattening. https://doi.org/10.1021/acsnano.0c08642

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