# Suppressed out-of-plane polarizability of free excitons in monolayer WSe$_{2}$

## TL;DR

This study demonstrates that free excitons in monolayer WSe2 exhibit extremely suppressed out-of-plane polarizability under strong electric fields, indicating strong electron confinement and robustness of excitons in 2D materials.

## Contribution

The paper provides the first experimental measurement showing suppressed out-of-plane polarizability of free excitons in monolayer WSe2, contrasting with previous reports on other 2D materials.

## Key findings

- Out-of-plane polarizability is less than 10^{-11} Dm/V
- Stark shift remains below 0.4 meV at high electric fields
- Free excitons are highly robust against surface potential fluctuations

## Abstract

Monolayer semiconductors are atomically thin quantum wells with strong confinement of electrons in two-dimensional (2D) plane. Here, we experimentally study the out-of-plane polarizability of excitons in hBN-encapsulated monolayer WSe$_{2}$ in strong electric fields of up to 1.6 V/nm (16 MV/cm). We monitor free and bound exciton photoluminescence peaks with increasing electric fields at a constant carrier density, carefully compensating for unintentional photodoping in our double-gated device at 4K. We show that the Stark shift is < 0.4 meV despite the large electric fields applied, yielding an upper limit of polarizability {\alpha}$_{z}$ to be ~ 10$^{-11}$ Dm/V. Such a small polarizability, which is nearly two orders of magnitude smaller than the previously reported value for MoS$_{2}$, indicates strong atomic confinement of electrons in this 2D system and highlights the unusual robustness of free excitons against surface potential fluctuations.

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Source: https://tomesphere.com/paper/1812.00675