Unveiling phase diagram of the lightly doped high-T-c cuprate superconductors with disorder removed

The currently established electronic phase diagram of cuprates is based on a study of single- and double-layered compounds. These CuO2 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 Ba2Ca5Cu6O12(F,O)(2) with inner CuO2 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. The phase diagram of cuprates is mostly based on data for single- and double-layered compounds in which the CuO2 planes are affected by the disorder. Here the authors report new features in the phase diagram of cuprates with low disorder by investigating the inner CuO2 planes of the six-layered compound.

Automated summary

By studying the inner CuO2 planes of a six-layered compound, the authors find that even the slightest amount of carriers can turn a Mott insulating state into a metallic state with long-lived quasiparticles. Furthermore, they observe a phase transition from the superconducting to the metallic states at 4% doping.