Effect of Coulomb interaction on transport gap in ideal graphene nanoribbons

S Ihnatsenka

doi:10.1063/5.0064512

Abstract

Quantum-mechanical calculations of electron transport in ideal graphene nanoribbons show that the transport gap that is predicted by noninteracting theories vanishes if the long-range Coulomb interaction between electrons is taken into account. This is a result of charge screening with the lowest subband edge being pinned to the chemical potential. However, the transport gap reappears if a ribbon is connected to wider leads, which is typically realized in an experimental setup that is based on lithographically patterned graphene ribbons. The gap is determined by scattering at the lead-to-ribbon interface, which can already be captured by the noninteracting theory.

Highlights

Quantum-mechanical calculations of electron transport in ideal graphene nanoribbons show that the transport gap that is predicted by noninteracting theories vanishes if the long-range Coulomb interaction between electrons is taken into account
While many studies focus on the role of disorder,[9,10,11,12] which undoubtedly exists in experimental samples, the presented results demonstrate that the gap even occurs in ideal, defectless graphene nanoribbons (GNRs) if they are connected to wide leads, which is a typical connection for lithographically patterned graphene samples.[2,3,4,5,6,7,8]
Quantum-mechanical calculations of electron transport in both noninteracting and interacting approaches predict that the semiconductor/metal alternation pattern that is widely discussed in the literature for armchair GNRs is much weaker and inverted for the setup with wide leads

Summary

Introduction

A transport gap in graphene nanoribbons (GNRs) is defined as the range of gate voltages for which source-to-drain conductance is suppressed at zero bias.[1,2,3,4] This has been observed in all experiments on graphene nanoribbons, regardless of width, crystallographic orientation, kind of subtract, and cleanness.[1,2,3,4,5,6,7,8] Careful analysis has shown that the main reason for the transport gap is edge disorder,[8,9,10,11,12] which is an imperfection of an edge profile when compared to the ideal atomic arrangement of either an armchair or zigzag for a hexagonal lattice. Rough edges cause localization of electronic states inside the ribbon, and transport is dominated by the hopping mechanism[3,4] or Coulomb blockade in a chain of quantum dots.[5,6] Other reasons include lattice defects and adsorbates in the bulk[7] and inhomogeneous potential due to charged impurities.[1,2,5,6] the strong impact of disorder on transport in GNRs has been recognized, one common feature of lithographically patterned ribbons has been overlooked—they are all connected to wide regions of graphene serving as the source and drain electrodes, and that connection might in itself cause electron scattering and contribute to the transport gap. One of the aims of the present study is to analyze how the interface between wide leads and a ribbon affects the transport gap

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Methods

Results

Discussion

Conclusion