A team of researchers, led by Klaus Ensslin and Thomas Ihn at the Laboratory for Solid State Physics at ETH Zurich, together with colleagues at the University of Texas in Austin (USA), has observed a novel state in twisted bi-layer graphene. In that state, negatively charged electrons and positively charged (so-called) holes, which are missing electrons in the material, are correlated so strongly with each other that the material no longer conducts electric current.
Image by Peter Rickhaus / ETH Zurich (taken from Nanowerk)
In conventional experiments, in which graphene layers are twisted by about one degree with respect to each other, the mobility of the electrons is influenced by quantum mechanical tunneling between the layers, explains Peter Rickhaus, a post-doc and lead author of the study. In our new experiment, by contrast, we twist two double layers of graphene by more than two degrees relative to each other, so that electrons can essentially no longer tunnel between the double layers.