DC Josephson Current through Nano-Graphite Ribbons

Abstract

The DC Josephson current through a nano-graphite ribbon placed between two conventional superconductors is theoretically studied by using thermal Green function techniques based on the tight binding model. The electronic states of nanographite ribbons strongly depend on the shapes of their edges, and give a single channel for the electron transport. The nanographite ribbons with zigzag boundaries have partly flat bands due to the edge states, in which the low-energy energy spectrum is a power function of ribbon width. The power-law partly flat bands induce the dependence of ribbon width on both the length dependence of the DC Josephson current and the coherence length. Also, because Andreev bound states highly accumulate close to the zero-energy level, the exponential decay of the DC Josephson current at the zero-energy level to the junction length strongly persists at very low temperatures.