2015/11/03 by Y. H. Jeong, Jeong, Y. H., S. -R. Eric Yang +1
Physics and Astronomy · #FOS: Physical sciences #Mesoscale and Nanoscale Physics (cond-mat.mes-hall) #cond-mat.mes-hall
paper · pdf · doi:10.48550/arxiv.1511.00805
7 pages, 9figures
arxiv created 2015/11/03 · arxiv updated 2015/11/04
A graphene nanoribbon is a good candidate for a (1+1) Chern-Simons topological insulator since it obeys particle-hole symmetry. We show that in a finite semiconducting armchair ribbon, which has two zigzag edges and two armchair edges, a (1+1) Chern-Simons topological insulator is indeed realized as the length of the armchair edges becomes large in comparison to that of the zigzag edges. But only a quasi-topological insulator is formed in a metallic armchair ribbon with a pseudogap. In such systems a zigzag edge acts like a domain wall, through which the polarization changes from 0 to e/2, forming a fractional charge of one-half. When the lengths of the zigzag edges and the armchair edges are comparable a rectangular graphene sheet (RGS) is realized, which also possess particle-hole symmetry. We show that it is a (0+1) Chern-Simons topological insulator. We find that the cyclic Berry phase of states of a RGS is quantized as π or 0 (mod 2π), and that the Berry phases of the particle-hole conjugate states are equal each other. By applying the Atiyah-Singer index theorem to a rectangular ribbon and a RGS we find that the lower bound on the number of nearly zero energy end states is approximately proportional to the length of the zigzag edges. However, there is a correction to this index theorem due to the effects beyond the effective mass approximation.