Evidence for Interlayer Electronic Coupling in Multilayer Epitaxial Graphene from Polarization Dependent Coherently Controlled Photocurrent Generation

TL;DR

This study uses polarization-dependent THz emission to reveal weak interlayer electronic coupling in multilayer epitaxial graphene, challenging the assumption of decoupled layers due to rotational stacking.

Contribution

It introduces a novel nonlinear optical method to probe interlayer coupling in multilayer graphene through third order nonlinear tensor measurements.

Findings

Polarization dependence indicates interlayer coupling.

Model calculations qualitatively match experimental polarization data.

Evidence suggests layers are weakly coupled, not fully decoupled.

Abstract

Most experimental studies to date of multilayer epitaxial graphene on C-face SiC have indicated that the electronic states of different layers are decoupled as a consequence of rotational stacking. We have measured the third order nonlinear tensor in epitaxial graphene as a novel approach to probe interlayer electronic coupling, by studying THz emission from coherently controlled photocurrents as a function of the optical pump and THz beam polarizations. We find that the polarization dependence of the coherently controlled THz emission expected from perfectly uncoupled layers, i.e. a single graphene sheet, is not observed. We hypothesize that the observed angular dependence arises from weak coupling between the layers; a model calculation of the angular dependence treating the multilayer structure as a stack of independent bilayers with variable interlayer coupling qualitatively reproduces the polarization dependence, providing evidence for coupling.