Subharmonic Gap Structure of Normal-State Conductance and Thermoelectric Effect in a Graphene-Based Nano Device

Abstract

Using the quantum transport of chiral Dirac fermions in graphene, we investigate the normal-state conductance and thermoelectric effect of a nano device under the ballistic superconductorgraphene-superconductor (SGS) model. Because of the Josephson effect and Andreev reflections, there exists an oscillatory behavior of the normal-state conductance flowing through the successive discrete energy levels on a finite-sized graphene contacted to the superconducting leads. The normal-state conductance displays a rich structure of subharmonic gaps controlled by means of a gate voltage on the discrete energy levels near the Fermi energy. Since the Fermi energy is an essential factor in determining the nature of conduction such as n or p type, we study the thermoelectric effect over the graphene-based nano device. It is shown that the thermoelectric effect can provide information on the location of the Fermi energy with respect to the energy levels of the finite-sized graphene.