Manchester team discovers “radically different” physics in graphene super lattices

A group of researchers led by Sir Andre Geim and Dr Alexey Berdyugin at the University of Manchester has discovered and characterized a new family of quasiparticles called “Brown-Zak fermions” in graphene-based super lattices.

The team achieved this breakthrough by aligning the atomic lattice of a graphene layer with that of a boron nitride insulating sheet, dramatically changing the properties of the graphene sheet.

The study follows years of successive advances in graphene-boron nitride superlattices, which allowed the observation of a fractal pattern known as the Hofstadter butterfly – and today (Friday, November 13), researchers are reporting very surprising behavior of particles in such structures. subjected to field magnets.

Changing trajectories

“It is known that in a zero magnetic field, electrons move in straight paths and if a magnetic field is applied, they begin to bend and move in a circle,” explained Julien Barrier (pictured below center), who did the work. experimental with Dr Piranavan Kumaravadivel (bottom right).

“In a layer of graphene that has been aligned with boron nitride, the electrons also start to bend – but if you set the magnetic field to specific values, the electrons again move in straight lines, as if there were none. more magnetic field! “

Dr Kumaravadivel added: “Such behavior is radically different from textbook physics.”

“We attribute this fascinating behavior to the formation of new high magnetic field quasiparticles,” said Dr. Alexey Berdyugin (top left). “Those quasiparticles have their own unique properties and exceptionally high mobility despite the extremely high magnetic field.”

The work describes how electrons behave in a very high quality graphene super lattice with a revised structure for the fractal characteristics of the Hofstadter butterfly. Fundamental improvements in graphene device fabrication and measurement techniques over the past decade have made this work possible.

New possibilities in superlattices

The authors propose that “Brown-Zak fermions” are the family of quasiparticles existing in high magnetic field super lattices. These Brown-Zak fermions define new metal states that are generic for any super lattice system, not just graphene, and offer a playground for new condensed matter physics problems into other material-based 2D super lattices.

Julien Barrier added: “The results are obviously important for fundamental studies on electron transport, but we believe that understanding quasiparticles in new super lattice devices under high magnetic fields can lead to the development of new electronic devices.”

Read the full report on our Graphene blog, or read the paper, Long-Range Ballistic Transport of Brown-Zak Fermions in Graphene Superlattices, as published in Nature Communications.

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