Electrically tunable transverse magnetic focusing in graphene

TL;DR

This paper demonstrates electrically tunable transverse magnetic focusing in high mobility graphene devices, revealing continuous control from hole to electron regimes and enabling room temperature electron-optic applications.

Contribution

First experimental observation of TMF in graphene with tunable carrier density and temperature, using TMF as a spectroscopy tool for electronic structure analysis.

Findings

TMF observed in mono-, bi-, and tri-layer graphene

TMF persists up to 300 K in graphene

TMF enables electronic structure investigation via electric field tuning

Abstract

Electrons in a periodic lattice can propagate without scattering for macroscopic distances despite the presence of the non-uniform Coulomb potential due to the nuclei. Such ballistic motion of electrons allows the use of a transverse magnetic field to focus electrons. This phenomenon, known as transverse magnetic focusing (TMF), has been used to study the Fermi surface of metals and semiconductor heterostructures, as well as to investigate Andreev reflection, spin-orbit interaction, and to detect composite fermions. Here we report on the experimental observation of transverse magnetic focusing in high mobility mono-, bi-, and tri-layer graphene devices. The ability to tune the graphene carrier density enables us for the first time to investigate TMF continuously from the hole to the electron regime and analyze the resulting focusing fan. Moreover, by applying a transverse electric field to tri-layer graphene, we use TMF as a ballistic electron spectroscopy method to investigate controlled changes in the electronic structure of a material. Finally, we demonstrate that TMF survives in graphene up to 300 K, by far the highest temperature reported for any system, opening the door to novel room temperature applications based on electron-optics.