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Alexis Coissard presents

 The many-body ground states of the graphene quantum Hall effect and their edge channels

Monday, 22 Novembre 2021 at 2:00 pm

Seminar room, Building A, Institut Néel : number of person limited to 30 

Zoom link : https://univ-grenoble-alpes-fr.zoom.us/j/96190000633?pwd=cWVRWFk1ZTR6Q0I1UHNiL0VIUSs2QT09

Meeting ID : 961 9000 0633
Code : 352692

The presentation will be in English.


Abstract :

Graphene exhibits a two dimensional electron gas directly exposed to vacuum, thus accessible by scanning tunneling microscopy (STM) and spectroscopy. In this PhD defense we present a systematic STM spectroscopy study performed on high-quality graphene samples, where the charge carrier density is tuned with a back-gate, and in which we have investigated the physics of the graphene quantum Hall regime under strong magnetic fields using a home-made AFM/STM operating at 4 K and up to 14 T. By carrying out high-resolution Landau level spectroscopy we unveil the pinning of the Fermi level in the Landau levels, a key phenomenon in the quantum Hall physics. We performed the first Landau level spectroscopy at the native edges of a graphene flake residing atop an insulating substrate and we show that the quantum Hall edge channels are confined in a few magnetic lengths from the graphene edges. When the Fermi level fills the zeroth Landau level, we observed the opening in the bulk of the interaction-induced gap at charge neutrality, resulting from a magnetic-like Stoner instability. This gap is found to be in excellent agreement with the Coulomb energy scale. We further show that the Coulomb interaction can be screened using a suitable high-k dielectric substrate. Last, scanning graphene at the atomic scale enabled us to image the lattice-scale orders of broken-symmetry states, which emerge in the zeroth Landau level as a function of the strength of the Coulomb interaction. Our results evidence a quantum phase transition driven by the substrate-screening of the Coulomb interaction.


Jury members : 
Christian Glattli, CEA Saclay
Dimitri Roditchev, ESPCI Paris
Mitali Banerjee, Ecole Polytechnique Fédérale de Lausanne
Clément Faugeras, LNCMI
Mark Oliver Goerbig, LPS