Imaging Cyclotron Orbits of Electrons in Graphene

TL;DR

This paper demonstrates imaging of electron cyclotron orbits in graphene using a cooled scanning gate microscope, revealing classical trajectories and flow patterns at low temperatures under magnetic focusing conditions.

Contribution

It introduces a method to directly image electron trajectories in graphene, combining magnetic focusing with scanning gate microscopy at cryogenic temperatures.

Findings

Imaged cyclotron orbits extending between contacts.

Observed magnetic focusing peaks as a function of magnetic field and electron density.

Studied orbit deflections caused by a local tip potential.

Abstract

Electrons in graphene can travel for several microns without scattering at low temperatures, and their motion becomes ballistic, following classical trajectories. When a magnetic field B is applied perpendicular to the plane, electrons follow cyclotron orbits. Magnetic focusing occurs when electrons injected from one narrow contact focus onto a second contact located an integer number of cyclotron diameters away. By tuning the magnetic field B and electron density n in the graphene layer, we observe magnetic focusing peaks. We use a cooled scanning gate microscope to image cyclotron trajectories in graphene at 4.2 K. The tip creates a local change in density that casts a shadow by deflecting electrons flowing nearby; an image of flow can be obtained by measuring the transmission between contacts as the tip is raster scanned across the sample. On the first magnetic focusing peak, we image a cyclotron orbit that extends from one point contact to the other. In addition, we study the geometry of orbits deflected into the second point contact by the tip.