Point-contact Andreev reflection tunneling spectroscopic (PCARTS) study on Ba$_{1-x}$K$_{x}$Fe$_{2}$As$_{2}$ and Ba(Fe$_{1-x}$Co$_{x})_{2}$As$_{2}$

PCARTS is applied to investigate the gap structure in the newly-discovered iron pnictide superconductors Ba$_{1-x}$K$_{x}$Fe$_{2}$As$_{2}$ and Ba(Fe$_{1-x}$Co$_{x})_{2}$As$_{2}$. Double peaks due to Andreev reflection with strongly-sloping background are frequently observed in the conductance curves G (V) for the Au-Ba$_{1-x}$K$_{x}$Fe$_{2}$As$_{2}$ point-contact junctions on the freshly-cleaved surface along the c-axis. . If normalized by the background baseline and analyzed by Blonder-Tinkham-Klapwijk model, the data show a gap size $\sim $ 4 meV with 2$\Delta $/k $_{B}$T$_{C }\sim $ 2.6. However, it is observed that, for the Ba(Fe$_{1-x}$Co$_{x})_{2}$As$_{2}$, G(V) curves evolve from V-shape to zero-bias conductance peak with increasing tip pressure, where the tip is likely to penetrate through surface layer. The existence of surface oxide layer is confirmed by comparative XPS characterization on freshly-cleaved and uncleaved surfaces.