Alkaline-earth iron arsenide (122) is one of the most studied families of iron-based superconductors, especially for angle-resolved photoemission spectroscopy. While extensive photoemission results have been obtained, the surface complexity of 122 caused by its charge-non-neutral surface is rarely considered. Here, we show that the surface of 122 can be neutralized by potassium deposition. In potassium-coated BaFe₂(As_0.7P_0.3)₂, the surface-induced spectral broadening is strongly suppressed, and hence the coherent spectra that reflect the intrinsic bulk electronic state recover. This enables the measuring of superconducting gap with unpreceded precision. The result shows the existence of two pairing channels. While the gap anisotropy on the outer hole/electron pockets can be well fitted using an s_± gap function, the gap anisotropy on the inner hole/electron shows a clear deviation. Our results provide quantitative constraints for refining theoretical models and also demonstrate an experimental method for revealing the intrinsic electronic properties of 122 in future studies.

碱土金属砷化铁（122）是铁基超导体研究最多的家族之一，尤其是用于角分辨光发射光谱学。尽管获得了广泛的光发射结果，但很少考虑由其非中性电荷表面引起的122表面复杂性。在这里，我们表明122的表面可以通过钾沉积来中和。在涂钾的BaFe ₂（As _0.7 P _0.3）_2中，表面诱导的光谱展宽被强烈抑制，因此反映本征体电子态的相干光谱得以恢复。这样就可以以前所未有的精度测量超导间隙。结果表明存在两个配对通道。虽然可以使用s _±间隙函数很好地拟合外孔/电子腔的间隙各向异性，但内孔/电子的间隙各向异性却显示出明显的偏差。我们的研究结果为完善理论模型提供了定量约束，并在未来的研究中证明了揭示122内在电子性质的实验方法。