Topological Crystalline Insulator Phase in Graphene Multilayers

While the experimental progress on three dimensional topological insulators is rapid, the development of their 2D counterparts has been comparatively slow, despite their technological promise. The main reason is materials challenges of the to date only realizations of 2D topological insulators, in semiconductor quantum wells. Here we identify a 2D topological insulator in a material which does not face similar challenges and which is by now most widely available and well charaterized: graphene. For certain commensurate interlayer twists, graphene multilayers are insulators with sizable band gaps. We show that they are moreover in a topological phase protected by crystal symmetry. As its fundamental signature, this topological state supports one-dimensional boundary modes. They form low-dissipation quantum wires that can be defined purely electrostatically.