Identifying the pairing symmetry in sodium cobalt oxide by Andreev edge states

TL;DR

This paper investigates how different pairing symmetries affect Andreev edge states in Na_xCoO_2.yH_2O, revealing their dependence on boundary topology and Fermi surface nodes, with predictions for experimental detection.

Contribution

It introduces a mapping from 2D to 1D models and elucidates the relationship between pairing symmetry, boundary topology, and edge state phase diagrams.

Findings

Phase diagram depends on pairing symmetry and boundary topology

Edge state structures are influenced by Fermi surface nodal points

Predicted measurable hot spots in Fourier-transformed STM

Abstract

We study the Andreev edge states with different pairing symmetries and boundary topologies on semi-infinite triangular lattice of Na_xCoO_2.yH_2O. A general mapping from the two dimensional lattice to the one dimensional tight-binding model is developed. It is shown that the phase diagram of the Andreev edge states depends on the pairing symmetry and also the boundary topology. Surprisingly, the structure of the phase diagram crucially relies on the nodal points on the Fermi surface and can be explained by an elegant gauge argument. We compute the momentum-resolved local density of states near the edge and predict the hot spots which are measurable in Fourier-transformed scanning tunneling spectroscopy.