Tunneling Conductance of Ba1-xKxFe2As2-GaAs Junction

We carried out point contact tunneling measurements by simply contacting degenerate GaAs semiconductor to polycrystalline Ba1-xKxFe2As2 with T-c = 31.1 +/- 1.0 K. The gap related structure was easily obtained. The gap value 2 Delta determined from peak-to-peak voltage was 18.0 meV, and 2 Delta/k(B)T(c) was 6.8. Small structures were observed at V similar to +/- 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 d(2)I/dV(2) and T-c, Delta in using Eliashberg equations by assuming alpha F-2(omega) from neutron phonon spectrum. The first phonon structure in calculated d(2)I/dV(2) is comparable to experimental one.