A team of researchers from Columbia University, City
University of New York, the University of Central Florida (UCF), and Tohoku University
and the National Institute for Materials Science in Japan, have directly
observed a rare quantum effect that produces a repeating butterfly-shaped
energy spectrum, confirming the longstanding prediction of this quantum fractal
energy structure called Hofstadter’s butterfly. The study, which focused on
moiré-patterned graphene, is published in the May 15, 2013, Advance Online
Publication (AOP) of Nature.