Optical conductivity study of screening of many-body effects in graphene interfaces

TL;DR

This study uses spectroscopic ellipsometry to measure and compare many-body electron interactions in graphene interfaces with insulators and metals, revealing how substrate screening affects these interactions.

Contribution

It demonstrates that spectroscopic ellipsometry can quantitatively assess electron-electron and electron-hole interactions in graphene interfaces, highlighting substrate-dependent screening effects.

Findings

In graphene on quartz, strong many-body interactions with a high effective fine structure constant (~1.37).

In graphene on copper, screening reduces interactions, lowering the effective constant at low energies.

Spectroscopic data enables quantification of interaction strength and substrate effects in graphene.

Abstract

Theoretical studies have shown that electron-electron (e-e) and electron-hole (e-h) interactions play important roles in many observed quantum properties of graphene making this an ideal system to study many body effects. In this report we show that spectroscopic ellipsometry can enable us to measure this interactions quantitatively. We present spectroscopic data in two extreme systems of graphene on quartz (GOQ), an insulator, and graphene on copper (GOC), a metal which show that for GOQ, both e-e and e-h interactions dominate while for GOC e-h interactions are screened. The data further enables the estimation of the strength of the many body interaction through the effective fine structure constant, $\alpha_{g}^{*}$. The $\alpha_{g}^{*}$ for GOQ indicates a strong correlation with an almost energy independent value of about 1.37. In contrast, $\alpha_{g}^{*}$ value of GOC is photon energy dependent, is almost two orders of magnitude lower at low energies indicating very weak correlation.