Graphene superlattices

Dr Leonid Ponomarenko, Physics

Tuesday 16 December 2014, 1555-1620
Lecture Theatre 1, Management School Building

Recent advances in the fabrication of heterostructures based on two-dimensional (2D) atomic crystals have opened up several new directions in graphene research1. One of the most exciting and highly debated subjects, which was initiated with direct involvement of the speaker2 and has been recognised by Physics World as one of 2013 breakthroughs of the year, is graphene superlattices.

These novel structures are made by aligning crystallographic axes of graphene and hexagonal boron nitride, which serves as the substrate. A small lattice mismatch between two materials results in a moiré pattern and leads to dramatic changes in the electronic properties of graphene.

The behaviour becomes even more interesting when the superlattice is placed in strong magnetic field. The electron spectrum starts to develop a fractal structure known as the Hofstadter butterfly, predicted almost four decades ago by American physicist Douglas Hofstadter3 and only now observed experimentally.

"Catching" of the Hofstadter butterfly is not easy. The magnetic field required for the experiment is 30 Tesla and it is available only at a handful of dedicated facilities across the globe. Established collaboration with the National High Magnetic Field Laboratory in Grenoble (France) will allow me to answer open questions about nature and behaviour of Hofstadter butterfly in graphene superlattices.

[1] A. K. Geim and I.V.Grigorieva. Nature 499, 419 (2013)

[2] L. A. Ponomarenko et al., Science 497, 594 (2013)

[3] D. R. Hofstadter, Phys. Rev. B 14, 2239 (1976)