Europhys. Lett.
Volume 69, Number 5, March 2005
Page(s) 791 - 797
Section Condensed matter: electronic structure, electrical, magnetic, and optical properties
Published online 11 February 2005
Europhys. Lett., 69 (5), pp. 791-797 (2005)
DOI: 10.1209/epl/i2004-10424-x

Andreev edge state on semi-infinite triangular lattice: Detecting the pairing symmetry in ${{\rm Na}_{0.35}{\rm CoO}_2}
\cdot y{{\rm H}_2{\rm O}}$

T. Pereg-Barnea1, 2 and H.-H. Lin1, 3

1  Kavli Institute for Theoretical Physics, University of California Santa Barbara, CA 93106,USA
2  Department of Physics and Astronomy, University of British Columbia Vancouver, B.C. V6T 1Z1, Canada
3  Physics Division, National Center for Theoretical Sciences - Hsinchu 300, Taiwan

received 12 October 2004; accepted in final form 10 January 2005
published online 11 February 2005

We study the Andreev edge state on the semi-infinite triangular lattice with different pairing symmetries and boundary topologies. We find a rich phase diagram of zero-energy Andreev edge states that is a unique fingerprint of each of the possible pairing symmetries. We propose to pin down the pairing symmetry in recently discovered $\chem{Na}$x $\chem{CoO_2}$ material by the Fourier-transformed scanning tunneling spectroscopy for the edge state. A surprisingly rich phase diagram is found and explained by a general gauge argument and mapping to 1D tight-binding model. Extensions of this work are discussed at the end.

74.78.-w - Superconducting films and low-dimensional structures.
74.20.-z - Theories and models of superconducting state.
74.45.+c - Proximity effects; Andreev effect; SN and SNS junctions.

© EDP Sciences 2005