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

¹ NUSNNI-NanoCore, National University of Singapore - Singapore 117576
² Department of Physics, National University of Singapore - Singapore 117542
³ Singapore Synchrotron Light Source, National University of Singapore 5 Research Link, Singapore 117603
⁴ Graphene Research Centre, Faculty of Science, National University of Singapore - Singapore 117546
⁵ Department of Chemistry, National University of Singapore - Singapore 117543
⁶ Department of Electrical and Computer Engineering, National University of Singapore - Singapore 117576

^(a) phyandri@nus.edu.sg

Received: 17 June 2012
Accepted: 18 August 2012

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, α*_g. The α*_g for GOQ indicates a strong correlation with an almost energy-independent value of about 1.37. In contrast, the α*_g value of GOC is photon energy dependent and is almost two orders of magnitude lower at low energies indicating very weak correlation.