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Marco GUERRA presents

Electron optics in ballistic graphene studied by scanning gate microscopy

Monday 28th of June 2021 at 9.30 am

Link : https://univ-grenoble-alpes-fr.zoom.us/j/94928514917?pwd=cmV6am1STG9KdkRtcHQ3eGE4ZzYvZz09

Amphi of the A Building: number of person limited to 30

The presentation will be in English.


Abstract :

Graphene p-n junctions are ideal platforms for electron optical experiment, where electron waves can experience negative refraction at the junction, described by an effective Snell-Descartes law for ultra relativistic Dirac fermions. This effect allows Veselago lensing, with the formation of a perfect focal point after the transmission of an electron beam through a potential step.

In this PhD thesis, I fabricated encapsulated graphene heterostructures equipped with a backgate made of pristine graphite, which provides straight electrostatic interface essential for refraction processes. We investigated refraction and reflection phenomena with a scanning gate microscope (SGM), unveiling real-space signatures of Veselago focusing, as well as unexpected frustrated total internal reflections. The observed data were corroborated with semi-classical transport simulations. Our work demonstrates that graphene is an excellent candidate for novel electron optical devices.

A second part of the PhD thesis is dedicated to SGM experiments providing spatial information on the backscattering between chiral quantum Hall edge states in graphene. We indentified real-space signatures of single-charge transport through a localized state, confirming its key role in the quantum Hall percolation through a disordered potential landscape.

Thesis Directors: Hermann Sellier & Benjamin Sacépé