Magnetic Phase Diagram of the Hole-doped Ca2−x_{2-x}Nax_{x}CuO2_{2}Cl2_{2} Cuprate Superconductor

We report on the magnetic phase diagram of a hole-doped cuprate Ca$_{2-x}$Na$_{x}$CuO$_{2}$Cl$_{2}$, which is free from buckling of CuO$_2$ planes, determined by muon spin rotation and relaxation. It is characterized by a quasi-static spin glass-like phase over a range of sodium concentration ($0.05\leq x\leq 0.12$), which is held between long range antiferromagnetic (AF) phase ($x\leq 0.02$) and superconducting phase where the system is non-magnetic for $x\geq 0.15$. The obtained phase diagram qualitatively agrees well with that commonly found for hole-doped high-\tc cuprates, strongly suggesting that the incomplete suppression of the AF order for $x>0.02$ is an essential feature of the hole-doped cuprates.Comment: 5 pages, submitted to Phys. Rev. Let

Visualizing the emergence of the pseudogap state and the evolution to superconductivity in a lightly hole-doped Mott insulator

Superconductivity emerges from the cuprate antiferromagnetic Mott state with hole doping. The resulting electronic structure is not understood, although changes in the state of oxygen atoms appear paramount. Hole doping first destroys the Mott state yielding a weak insulator where electrons localize only at low temperatures without a full energy gap. At higher doping, the 'pseudogap', a weakly conducting state with an anisotropic energy gap and intra-unit-cell breaking of 90\degree-rotational (C4v) symmetry appears. However, a direct visualization of the emergence of these phenomena with increasing hole density has never been achieved. Here we report atomic-scale imaging of electronic structure evolution from the weak-insulator through the emergence of the pseudogap to the superconducting state in Ca2-xNaxCuO2Cl2. The spectral signature of the pseudogap emerges at lowest doping from a weakly insulating but C4v-symmetric matrix exhibiting a distinct spectral shape. At slightly higher hole-density, nanoscale regions exhibiting pseudogap spectra and 180\degree-rotational (C2v) symmetry form unidirectional clusters within the C4v-symmetric matrix. Thus, hole-doping proceeds by the appearance of nanoscale clusters of localized holes within which the broken-symmetry pseudogap state is stabilized. A fundamentally two-component electronic structure11 then exists in Ca2-xNaxCuO2Cl2 until the C2v-symmetric clusters touch at higher doping, and the long-range superconductivity appears.Comment: See the Nature Physics website for the published version available at http://dx.doi.org/10.1038/Nphys232