Separation between long- and short-range part of the Coulomb interaction in low dimensional systems: implications for the macroscopic screening length and the collective charge excitations

TL;DR

This paper develops a method to distinguish long- and short-range Coulomb interactions in low-dimensional systems, enabling accurate analysis of collective charge excitations and screening lengths from first-principles calculations, with applications to 2D materials.

Contribution

It introduces a novel approach to separate Coulomb interaction ranges in low-dimensional systems, facilitating the study of collective excitations and screening effects from microscopic data.

Findings

Successfully applied to 2D materials like NbSe2, BN, and MoS2.

Enabled extraction of macroscopic screening lengths from first-principles calculations.

Provided a framework to analyze collective charge excitations in low-dimensional systems.

Abstract

Collective charge excitations directly probed in electron energy loss and inelastic X rays scattering spectroscopies play a key role in different fields of condensed matter physics. Being induced by the long-range part of the Coulomb interaction between particles, in standard bulk systems they appear as well-defined features in the spectra associated to the zero crossing of the real part of the macroscopic dielectric function. However, this simple criterion cannot be used to identify collective excitations in low dimensional systems where the macroscopic dielectric function is not a well defined concept. In this work, we discuss how this problem can be traced back to the definition of the long-range Coulomb interaction and we show how the appropriate separation between long- and short-range Coulomb interaction allows one to correctly express the low dimensional macroscopic dielectric function in terms of microscopic quantities accessible in first-principles calculations. This allows disentangling collective charge excitations in low dimensional materials in analogy with what one does in standard bulk systems. In addition, we show how important macroscopic quantities, such as the screening length scale, can be extracted from full first principle calculations. As an illustrative example we perform a study of the screening effects and the collective excitations in prototypical 2D materials including metals (NbSe2) as well as semiconductors (BN and MoS2).