Dielectric screening in two-dimensional insulators: Implications for excitonic and impurity states in graphane

TL;DR

This paper derives an exact analytic form of the screened potential in 2D insulators, revealing nonlocal screening effects that influence excitonic and impurity states, with implications for electronic applications.

Contribution

It provides a simple, accurate model for 2D dielectric screening that matches complex many-body calculations and explains impurity localization in graphane.

Findings

Screened potential in 2D insulators shows nonlocal behavior with a logarithmic divergence.

Impurity hole-doping in graphane causes strongly localized states.

A simple p approach effectively describes electronic properties despite nonlocal screening.

Abstract

For atomic thin layer insulating materials we provide an exact analytic form of the two-dimensional screened potential. In contrast to three-dimensional systems where the macroscopic screening can be described by a static dielectric constant in 2D systems the macroscopic screening is non local (q-dependent) showing a logarithmic divergence for small distances and reaching the unscreened Coulomb potential for large distances. The cross-over of these two regimes is dictated by 2D layer polarizability that can be easily computed by standard first-principles techniques. The present results have strong implications for describing gap-impurity levels and also exciton binding energies. The simple model derived here captures the main physical effects and reproduces well, for the case of graphane, the full many-body GW plus Bethe-Salpeter calculations. As an additional outcome we show that the impurity hole-doping in graphane leads to strongly localized states, what hampers applications in electronic devices. In spite of the inefficient and nonlocal two-dimensional macroscopic screening we demonstrate that a simple $\mathbf{k}\cdot\mathbf{p}$ approach is capable to describe the electronic and transport properties of confined 2D systems.