Uniform Mixing of Antiferromagnetism and High-Temperature Superconductivity in Electron-Doped Layers of Four-Layered Ba_2Ca_3Cu_4O_8F_2: A New Phenomenon in an Electron Underdoped Regime

摘要

We report ~(63,65)Cu- and ~(19)F-NMR studies on a four-layered high-temperature superconductor Ba_2Ca_3Cu_4O_8F_2((0234F(2.0)) with apical fluorine (F~(-1)), an undoped 55 K superconductor with a nominal Cu~(2+) valence on average. We reveal that this compound exhibits the antiferromagnetism (AFM) with a Neel temperature T_N = 100 K despite being a T_c = 55 K superconductor. Through a comparison with a related trilayered cuprate Ba_2Ca_2Cu_3O_6F_2(0233F(2.0)), it is demonstrated that electrons are transferred from the inner plane (IP) to the outer plane (OP) in 0234F(2.0) and 0223F(2.0), confirming the self-doped high-temperature superconductivity (HTSC) having electron and hole doping in a single compound. Remarkably, uniform mixing of AFM and HTSC takes place in both the electron-doped OPs and the hole-doped IPs in 0234F(2.0).