The superconductivity in high temperature supercon-ductors ordinarily arises when doped with hetero-valent ions that introduce charge carriers [1-4]. However, in ferropnictides, "iso-valent" doping, which is generally believed not to introduce charge carriers, can induce superconductivity as well [5-11]. Moreover, unlike other ferropnictides [12, 13], the superconducting gap in BaFe 2 (As 1−x P x) 2 has been found to contain nodal lines [14-16]. The exact nature of the "iso-valent" doping and nodal gap here are key open issues in building a comprehensive picture of the iron-based high temperature supercon-ductors [17-20]. With angle-resolved photoemission spec-troscopy (ARPES), we found that the phosphor substitution in BaFe 2 (As 1−x P x) 2 induces sizable amount of holes into the hole Fermi surfaces, while the d xy-originated band is relatively intact. This overturns the previous common belief of "iso-valent" doping, explains why the phase diagram of BaFe 2 (As 1−x P x) 2 is similar to those of the hole-doped compounds, and rules out theories that explain the nodal gap based on vanishing d xy hole pocket. BaFe 2 (As 1−x P x) 2 is a rather unique ferropnictide as its su-perconductivity is introduced by the iso-valent doping of P for As [5, 6]. Unlike the hetero-valent doping that alters the carrier concentration in Ba 1−x K x Fe 2 As 2 , BaFe 2−x Co x As 2 , or LaO 1−x F x FeAs [2-4], the iso-valent doping is often considered not to alter the occupation of the Fe 3d bands, as illustrated by the density functional theory calculations of BaFe 2 As 2 and BaFe 2 P 2 as well [6, 7]. Yet, surprisingly, it has a similar phase diagram just like the hetero-valent doped cases: with P doping, spin density wave (SDW) is suppressed and superconductivity (SC) emerges [6]. Since P anion is smaller than As anion, and thus introduces internal strain or distortion, i.e. chemical pressure, the su-perconductivity introduced by iso-valent doping is associated with the unprecedented pressure dependence of the supercon-ducting transition temperature (T c) generally observed in iron-based superconductors [21-24]. In fact, it is the largest among all superconductors in both relative and absolute scales. For example, a T c dependency of 2-4K/GPa and sometimes even 10K/GPa is observed in BaFe 2 (As 1−x P x) 2 , LaO 1−x F x FeAs, etc. [21, 22]; and an increase of T c from 0 to above 30 K is observed in BaFe 2 As 2 and FeSe under pressure [23, 24]. However, these remarkable pressure effects are still far from understood. Theoretically, P doping is predicted to alter the band structure and Fermi surface topology dramatically, considering it changes the electron hopping terms [17, 25]. Particularly , it is predicted that the d z 2-based band would go above the Fermi energy (E F), while the d xy-based band would move down below E F with P doping. Several theories further claim that nodes will appear in the superconducting gap when the d xy hole Fermi pocket disappears [17-19]. Figure 1 examines the dependence of the Fermi surfaces on the P co...
