Abstract
We construct the symmetry adapted low-energy effective Hamiltonian for the electronic states in the vicinity of the Fermi level in iron-based superconductors. We use Luttinger's method of invariants, expanding about and points in the Brillouin zone corresponding to a two-iron unit cell, and then matching the coefficients of the expansion to the five- and eight-band models. We then use the method of invariants to study the effects of the spin-density wave order parameters on the electronic spectrum, with and without spin-orbit coupling included. Among the results of this analysis is the finding that the nodal spin-density wave is unstable once spin-orbit coupling is included. Similar analysis is performed for the spin singlet superconducting state. Without spin-orbit coupling there is one pairing invariant near the point but two near the point. This leads to an isotropic spectral gap at the hole Fermi surface near , but anisotropic near . The relative values of these three parameters determine whether the superconducting state is , , or nodal. Inclusion of spin-orbit coupling leads to additional mixing of spin triplet pairing, with one additional pairing parameter near and one near . This leads to an anisotropic spectral gap near both hole and electron Fermi surfaces, the latter no longer cross but rather split.
11 More- Received 18 April 2013
DOI:https://doi.org/10.1103/PhysRevB.88.134510
©2013 American Physical Society