Coulomb potential screening via charged carriers and charge-neutral dipoles/excitons in two-dimensional case

TL;DR

This paper develops an analytical model for Coulomb potential screening in 2D materials considering both charge carriers and dipoles, providing insights into exciton behavior and aiding electronic and optoelectronic device design.

Contribution

It introduces a comprehensive linear response theory-based solution for Coulomb screening in 2D systems, extending beyond traditional models to include neutral dipoles.

Findings

The model accurately predicts exciton binding energy variations.

It aligns well with computational and experimental data.

Provides a practical tool for analyzing Coulomb interactions in 2D materials.

Abstract

With the shrinking of dimensionality, Coulomb interactions play a distinct role in two-dimensional (2D) semiconductors owing to the reduced dielectric screening in the out-of-plane direction. Apart from dielectric screening, free charge carriers and/or dipoles can also make a non-negligible contribution to Coulomb interaction. While the Thomas-Fermi model is effective in describing charge carrier screening in three dimensions, the extent of screening to two dimensions resulting from charge carriers and charge-neutral dipoles remains quantitatively unclear. Herein, we present an analytical solution based on linear response theory, offering a comprehensive depiction of the Coulomb screened potential in both 2D and 3D systems, where screening effects from both charge carriers and charge-neutral dipoles are addressed. Our work provides a useful and handy tool for directly analysing and evaluating Coulomb interaction strength in atomically thin materials, particularly in the context of electronic and optoelectronic engineering. As a demonstration, we utilized the derived modified Coulomb potential for the exciton system in 2D semiconductors to estimate the exciton binding energy variation arising from the exciton density fluctuation and temperature-dependent exciton polarizability, yielding excellent agreement with the computational and experimental findings.