Using a novel technique to fabricate bilayer graphene devices with ultra-high mobility we observe the fractional quantum Hall effect and demonstrate that the associated ground state is tunable by application of a transverse displacement field. Our result was featured on the cover of science!
When graphene is placed in contact with hexagonal boron, a moire pattern develops with long range order, which in turn looks like a crystal field to the free electrons in the graphene layer. We were able to exploit the large length-scale of the moire superlattice (~15 nm) to observe the long predicted Hofstadter butterfly fractal energy spectrum - a result physicists have been chasing for more than 30 years! Our resuls appeared in the magazine Nature .
-UPDATE- Physics world has identified our results as one of the "top ten breakthroughs of 2013".