Experimental evidence of plasmarons and effective fine structure constant in electron-doped graphene/h-BN heterostructure

Hongyun Zhang,Kenji Watanabe,Jonathan D Denlinger,Takashi Taniguchi,Eryin Wang,Haoxiong Zhang,Alexei V Fedorov,Guorui Chen,Guangyu Zhang,Shuyun Zhou,Changhua Bao,Xiaobo Lu,Wei Yao,Qian Li,Shuopei Wang,Ke Deng

doi:10.1038/s41535-021-00386-7

Abstract

Electron-electron interaction is fundamental in condensed matter physics and can lead to composite quasiparticles called plasmarons, which strongly renormalize the dispersion and carry information of electron-electron coupling strength as defined by the effective fine structure constant {alpha }_{ee}^{* }. Although h-BN with unique dielectric properties has been widely used as an important substrate for graphene, so far there is no experimental report of plasmarons in graphene/h-BN yet. Here, we report direct experimental observation of plasmaron dispersion in graphene/h-BN heterostructures through angle-resolved photoemission spectroscopy (ARPES) measurements upon in situ electron doping. Characteristic diamond-shaped dispersion is observed near the Dirac cone in both 0° (aligned) and 13.5° (twisted) graphene/h-BN, and the electron-electron interaction strength {alpha }_{ee}^{* } is extracted to be {alpha }_{ee}^{* }approx 0.9pm 0.1, highlighting the important role of electron-electron interaction. Our results suggest graphene/h-BN as an ideal platform for investigating strong electron-electron interaction with weak dielectric screening, and lays fundamental physics for gate-tunable nano-electronics and nano-plasmonics.

Highlights

Electron-electron interaction is ubiquitous in solids and plays an important role in condensed matter physics
This ratio defines a fundamental constant αÃee 1⁄4 U=K 1⁄4 e2=ε_vF4,5, which is in analogy to the fine structure constant α = e2/ħc = 1/137 in quantum electrodynamics, with the speed of light c replaced by the Fermi velocity vF and the effective dielectric screening of the environment taken into account by ε
Electron-electron interaction can significantly affect the electronic dispersion by reshaping the graphene Dirac cone dispersion with a modified Fermi velocity[8,9,10,11]

Summary

Introduction

Electron-electron interaction is ubiquitous in solids and plays an important role in condensed matter physics. The strength of the electron-electron interaction is quantified by the ratio of the Coulomb potential U = e2kF/ε to the kinetic energy K = ħvFkF1–3, where vF and kF are the Fermi velocity and Fermi momentum respectively, and ε is the dielectric constant. This ratio defines a fundamental constant αÃee 1⁄4 U=K 1⁄4 e2=ε_vF4,5, which is in analogy to the fine structure constant α = e2/ħc = 1/137 in quantum electrodynamics, with the speed of light c replaced by the Fermi velocity vF and the effective dielectric screening of the environment taken into account by ε. Since the energy and momentum separation between the Dirac cone and plasmaron bands is determined by the observing plasmaron defisfepcetrisvieonfianlelowsstrutoctuerxetraccot nαsÃeteanetxpαeÃereim14e–1n8-, tally, which is critical for revealing the fundamental physics of electron-electron interaction in graphene-based electronics and plasmonics

Methods

Results

Conclusion