Gate-tunable Topological Pseudospin Transport in Bilayer Graphene

Extra quantum degree of freedom, generally referred to as pseudospin, arises in condensed matter systems when electrons from two sublattices of a crystal form degenerate bands at Fermi level. Here we describe a pseudospin system based on the ``which-layer'' quantum degree of freedom in bilayer graphene that is fully tuned by top and bottom gates. We detect topological pseudospin current - a result of the broken symmetry induced by the top and bottom gate electric fields - in a nonlocal geometry. The nonlocal pseudospin transport persists up to room temperature owing to the large, tunable band gap in our bilayer graphene devices. The gate-tunable pseudospin quantum degree of freedom in bilayer graphene may lead to future pseudospin-based electronic applications.