Suppressed Out-of-Plane Polarizability of Free Excitons in Monolayer WSe<sub>2</sub>.
basic_science · Level V
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- Record sourced from PubMed, PMID 30768242.
- Also identified by DOI 10.1021/acsnano.8b08905.
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Abstract
Monolayer semiconductors are atomically thin quantum wells with strong confinement of electrons in a two-dimensional (2D) plane. Here, we experimentally study the out-of-plane polarizability of excitons in hBN-encapsulated monolayer WSe<sub>2</sub> in strong electric fields of up to 1.6 V/nm (16 MV/cm). We monitor free exciton photoluminescence peaks with increasing electric fields at a constant carrier density, carefully compensating for unintentional photodoping in our double-gated device at 4 K. We show that the Stark shift is smaller than 0.4 meV despite the large electric fields applied, yielding an upper limit of polarizability α <sub>z</sub> to be ∼10<sup>-11</sup> Dm/V. Such a small polarizability, which is nearly two orders of magnitude smaller than the previously reported value for MoS<sub>2</sub>, indicates strong atomic confinement of electrons in this 2D system and highlights the unusual robustness of free excitons against surface potential fluctuations.