A tunable electronic beam splitter realized with crossed graphene nanoribbons

Pedro Brandimarte,Mads Engelund,Nick Papior,Daniel Sánchez-Portal,Thomas Frederiksen,Aran Garcia-Lekue

doi:10.1063/1.4974895

Abstract

Graphene nanoribbons (GNRs) are promising components in future nanoelectronics due to the large mobility of graphene electrons and their tunable electronic band gap in combination with recent experimental developments of on-surface chemistry strategies for their growth. Here, we explore a prototype 4-terminal semiconducting device formed by two crossed armchair GNRs (AGNRs) using state-of-the-art first-principles transport methods. We analyze in detail the roles of intersection angle, stacking order, inter-GNR separation, GNR width, and finite voltages on the transport characteristics. Interestingly, when the AGNRs intersect at θ=60°, electrons injected from one terminal can be split into two outgoing waves with a tunable ratio around 50% and with almost negligible back-reflection. The split electron wave is found to propagate partly straight across the intersection region in one ribbon and partly in one direction of the other ribbon, i.e., in analogy with an optical beam splitter. Our simulations further identify realistic conditions for which this semiconducting device can act as a mechanically controllable electronic beam splitter with possible applications in carbon-based quantum electronic circuits and electron optics. We rationalize our findings with a simple model suggesting that electronic beam splitters can generally be realized with crossed GNRs.

Highlights

We discovered that when the two armchair GNRs (AGNRs) cross at an intersection angle θ = 60◦, a substantial current can be passed from one ribbon to the other and, that electrons injected from one terminal can be split into two outgoing waves with a tunable ratio around 50% and with almost negligible back-reflection
We will refer to the AGNR attached to the electrodes 1 and 2 as GNR12 and, analogously, the ribbon attached to the electrodes 3 and 4 as GNR34
In this paper we studied the electronic and transport properties of a 4-terminal junction defined by two crossed AGNRs from first-principles with the Siesta/TranSiesta codes

Summary

Introduction

The wave nature of electrons that propagate coherently in ballistic, one-dimensional conductors has certain qualities in common with photons propagating in vacuum. This analogy has spawned the field of electron quantum optics, in which a number of optical setups have been realized in the form of their electronic counterparts, such as the Hanbury Brown and Twiss geometry for studies of Fermion anti-bunching and the two-particle Aharanov-Bohm effect as well as Mach–Zehnder interferometry with charged quasiparticles. The advent of coherent single-particle sources and entangled electron pair generators has further provided exciting possibilities for novel quantum technologies and information processing.Graphene nanoribbons (GNRs) have some highly desirable properties for their use in molecular-scale electronics devices—they can be designed with specific band gaps and long defect-free samples can be fabricated with both armchair (AGNR) and zigzag (ZGNR) edge topology via on-surface synthesis. The wave nature of electrons that propagate coherently in ballistic, one-dimensional conductors has certain qualities in common with photons propagating in vacuum.. The wave nature of electrons that propagate coherently in ballistic, one-dimensional conductors has certain qualities in common with photons propagating in vacuum.1 This analogy has spawned the field of electron quantum optics, in which a number of optical setups have been realized in the form of their electronic counterparts, such as the Hanbury Brown and Twiss geometry for studies of Fermion anti-bunching and the two-particle Aharanov-Bohm effect as well as Mach–Zehnder interferometry with charged quasiparticles.. In the standard bottom-up approach it is difficult to fully explore the GNR electronic properties due to interactions with the metallic substrates used for the synthesis. Simple 4-terminal tunneling junctions can be fabricated by crossing 1D-structures such as carbon nanotubes or GNRs. in the context of electron

Results

Discussion

Conclusion