Resources

Some images to illustrate my results. Click on the images to get a high resolution picture. Unless otherwise specified, the images are under a CC-by-sa license. That means you’re able to copy, share and redistribute these images, as long as you provide appropriate credit (Julien Barrier) and share under the same license as the original.

Graphene superlattices

The following drawings present a graphene layer (blue) stacked with an hexagonal boron nitride (magenta) layer (hBN, sometimes referred to as white graphene). The stacking for aligned sheets presents a Moiré pattern, with a superlattice covering several nanometers.

graphene - hBN superlattice
superlattice-01

Here the superlattice structure is drawn in black:

graphene - hBN superlattice
superlattice-02

Brown-Zak Fermions

Brown-Zak fermions represent the family of quasiparticles appearing in moiré superlattices exposed to high magnetic fields. More details are given here and here.

The following image represents different transport regime of quasiparticle in graphene and graphene superlattices:

  • Left: an electron in a graphene sheet propagates in straight trajectories when a current is applied through the material;
  • Center: when a magnetic field is applied, perpendicular to the sheet, the electrons have circular orbits;
  • Right: For some exact values of the magnetic field in graphene-hBN lattices, we observe Brown-Zak fermions, that have a straight trajectory despite the high magnetic field. This translates in a lower resistance of the device.
Brown Zak fermion Julien Barrier electron trajectory
BrownZakfermions-01

The following picture adds a doping vs magnetic field conductance map: The magnetic field is varied along the vertical axis. Horizontal Yellow streaks show propagation of Brown-Zak fermions, propagating along straight trajectories with high mobility (low resistance), whereas slanted indigo lines show the cyclotron motion around Brown-Zak fermions. The slope of these lines enabled us to get the degeneracy (and find an additional quantum number) of these new quasiparticles.

Brown-Zak fermion Julien Barrier trajectory
BrownZakfermions-02

And with a magnetic field axis:

Brown-Zak fermion Julien Barrier magnetic field
BrownZakfermions-03

Here, only the doping vs magnetic field map is shown.

Brown-Zak fermion Julien Barrier conductance map Landau levels
BrownZakfermions-04

Personal pictures

Julien Barrier portrait
JulienBarrier-01

In the condensed matter physics laboratory at the University of Manchester:

Julien Barrier portrait photo laboratory science
JulienBarrier-02, © Steve Forrest for l'Usine Nouvelle. Contact him for reproduction rights.
Julien Barrier portrait photo laboratory science
JulienBarrier-03, © Steve Forrest for l'Usine Nouvelle. Contact him for reproduction rights.

Public speaking:

Julien Barrier portrait photo public speaking
JulienBarrier-04