Tunneling Conductance of Ba 1− x K x Fe 2 As 2 –GaAs Junction

We carried out point contact tunneling measurements by simply contacting degenerate GaAs semiconductor to polycrystalline Ba1−x K x Fe2As2 with T c=31.1±1.0 K. The gap related structure was easily obtained. The gap value 2Δ determined from peak-to-peak voltage was 18.0 meV, and 2Δ/k B T c was 6.8. Small structures were observed at V∼±23 mV in the conductance curve separately from the gap edge structure. These values are included in phonon energy region and correspond to a peak of phonon density of states. Thus, the structures are attributed to phonon structure. We calculated d2 I/dV 2 and T c, Δ in using Eliashberg equations by assuming α 2 F(ω) from neutron phonon spectrum. The first phonon structure in calculated d2 I/dV 2 is comparable to experimental one.