Andreev bound states in sodium cobalt oxide

We study the Andreev bound states with different pairing symmetries and boundary topologies on semi-infinite triangular lattice of the sodium cobalt oxide. A general mapping from the two dimensional lattice to the one-dimensional tight-binding model is developed. Due to the hidden structure of these effective one-dimensional models, the Andreev bound states can be categorized into the positive and negative Witten parity states in supersymmetric algebra. By solving these parity states, the momentum-resolved local density of states near the edge is revealed and can be used to predict the position of the sharp peaks that can be observed in FT-STS experiments. (C) 2009 Elsevier B.V. All rights reserved.