Unveiling phase diagram of the lightly doped high-Tc cuprate superconductors with disorder removed
Kifu Kurokawa, Shunsuke Isono, Yoshimitsu Kohama, So Kunisada, Shiro Sakai, R. Sekine, Makoto Okubo, Matthew D. Watson, T. K. Kim, Céphise Cacho, Shik Shin, Takami Tohyama, K. Tokiwa, Takeshi Kondo
Abstract
Abstract The currently established electronic phase diagram of cuprates is based on a study of single- and double-layered compounds. These CuO 2 planes, however, are directly contacted with dopant layers, thus inevitably disordered with an inhomogeneous electronic state. Here, we solve this issue by investigating a 6-layered Ba 2 Ca 5 Cu 6 O 12 (F,O) 2 with inner CuO 2 layers, which are clean with the extremely low disorder, by angle-resolved photoemission spectroscopy (ARPES) and quantum oscillation measurements. We find a tiny Fermi pocket with a doping level less than 1% to exhibit well-defined quasiparticle peaks which surprisingly lack the polaronic feature. This provides the first evidence that the slightest amount of carriers is enough to turn a Mott insulating state into a metallic state with long-lived quasiparticles. By tuning hole carriers, we also find an unexpected phase transition from the superconducting to metallic states at 4%. Our results are distinct from the nodal liquid state with polaronic features proposed as an anomaly of the heavily underdoped cuprates.