Determining gap nodal structures in Fe-based superconductors: Theory of the angle dependence of the low-temperature specific heat in an applied magnetic field

Since the discovery of high-T_c LaO_1−xF_xFeAs and other such systems based on FeAs layers, several proposals have been made for the superconducting order parameter Δ_k, on both phenomenological and microscopic grounds. Here we discuss how the symmetry of Δ_k in the bulk can be determined, assuming that single crystals will soon be available. We suggest that a measurement of the dependence of the low-temperature specific heat on the angle of a magnetic field in the FeAs plane is the simplest such method, and calculate representative specific heat vs field angle oscillations for the various candidate states, using a phenomenological band structure fitted to the density functional theory Fermi surface.