Determination of the pairing state in iron-based superconductors through neutron scattering

We calculate the spin susceptibility in the s_{+-} and s_{++} superconducting states of the iron pnictides using the effective five orbital model and considering the quasiparticle damping. For the experimentally evaluated magnitude of the quasiparticle damping and the superconducting gap, the results at the wave vector ~ (pi,0) show that the s_{+-} state is more consistent with the neutron scattering experiments, while for larger quasiparticle damping and the superconducting gap, the s_{++} state can be more consistent. To distinguish between two cases that reproduce the experiments at the wave vector ~ (pi,0), we propose to investigate experimentally the wave vector ~ (pi,pi).Comment: 5pages, 3 figures, Accepted in Phys. Rev.

Inhomogeneity Effects in Topological Superconductors

We have constructed a quasiclassical framework on superconductors with strong spin-orbit couplings, applicable to CuxBi2Se3[Y. Nagai, H. Nakamura, and M. Machida: arXiv:1305.3025]. The notable point is that in this framework the Bogoliubov-de Gennes Hamiltonians with suggested odd-parity pairing states turn to quasiclassical ones with usual spin-triplet Cooper pairs. Using this quasiclassical theory, we can investigate inhomogeneity effects such as the phenomena with vortices and surfaces in this superconductors and shed light on the pairing state of topological superconductors. In this paper, we apply the quasiclassical framework to the surface bound states with the Dirac-cone energy dispersion originated from the topological invariant in the parent compound Bi2Se3 in order to investigate the robustness of these bound states under the superconducting order parameter. The odd-parity gap functions can not open on the Dirac-cone-dispersion band in the Cu-doped Bi$_{2}$Se$_{3}$ superconductor. We show that the massless Dirac quasiparticles originated from the normal-state topological invariant and the Majorana quasiparticles coexist with each other on the surface in the odd-parity topological superconductivity. Inhomogeneity effects can be easily investigated with the use of our quasiclassical framework in topological superconductors.Comment: 6 pages, 2 figures, submitted to SCES 2013 proceeding