Vortex State in Na_xCoO_2.yH_2O: p_x\pm ip_y-wave versus d_{x^2-y^2}\pm id_{xy}-wave Pairing

TL;DR

This study investigates the vortex states in Na_xCoO_2·yH_2O using effective Hamiltonians and Bogoliubov-de Gennes equations, revealing distinct vortex structures and bound states for different pairing symmetries, with implications for experimental detection.

Contribution

It introduces a detailed analysis of vortex states in Na_xCoO_2·yH_2O considering p+ip and d+id pairing symmetries, highlighting their unique vortex structures and magnetic orders.

Findings

p_x± ip_y-wave favored for t<0 doping

Vortex bound states differ in energy for the two pairing types

Magnetic orders induced around vortex cores

Abstract

Based on an effective Hamiltonian specified in the triangular lattice with possible $p_x\pm ip_y$- or $d_{x^2-y^2}\pm id_{xy}$-wave pairing, which has close relevance to the newly discovered Na$_{0.35}$CoO$_2$$\cdot y$H$_2$O, the electronic structure of the vortex state is studied by solving the Bogoliubov-de Gennes equations. It is found that $p_x\pm ip_y$-wave is favored for the electron doping as the hopping integral $t<0$. The lowest-lying vortex bound states are found to have respectively zero and positive energies for $p_x\pm ip_y$- and $d_{x^2-y^2}\pm id_{xy}$-wave superconductors, whose vortex structures exhibit the intriguing six-fold symmetry. In the presence of strong on-site repulsion, the antiferromagnetic and ferromagnetic orders are induced around the vortex cores for the former and the latter, respectively, both of which cause the splitting of the LDOS peaks due to the lifting of spin degeneracy. STM and NMR measurements are able to probe the new features of vortex states uncovered in this work.