Scanning tunneling spectroscopy of SrFe₂(As_1-xP_x)₂

The antiferromagnetic parent compound SrFe₂As₂ shows a supression of the spin density wave and a subsequent superconducting state upon partial substitution of As by P. We investigated single crystals for four different P-concentrations x in the superconducting (x=0.35,0.46) as well as in the spin density wave phase (x=0,0.2). The superconducting samples display a v-shaped superconducting gap, which suggests nodal superconductivity in this system. Furthermore, we were able to determine the superconducting coherence length by measuring the spatial resolved superconducting density of states. From inelastic tunneling spectra it is possible to determine the Eliashberg function from the normal state. We thus investigated bosonic excitations for the four different P-concentrations. Indeed, evidence suggests peaks which can be related to bosonic modes. The phonon an non-phonon mechanism for the origin of these peaks will be discussed.