Spin excitations in the fully gapped hybridized two band superconductor

Abstract In f -electron heavy fermion superconductors the presence of a spin resonance in the inelastic magnetic response is commonly associated with an unconventional nodal gap function that is not fully symmetric. However it appears possible that the resonance is still observed even when the low temperature thermodynamic behavior suggests a fully gapped state. We investigate such possibility within a two-dimensional toy model of a hybridized superconductor with a fully symmetric s ± unconventional symmetry with different sign of the gap function on disjoint Fermi surface sheets. We compute the collective magnetic response function in the hybridized superconducting state of the two-band model and show that the appearance of the resonance is also possible for the fully gapped state.