Arguably the most intriguing aspect of the physics of cuprates is the close proximity between the record high-Tc superconductivity (HTSC) and the antiferromagnetic charge-transfer insulating state driven by Mott-like electron correlations. These are
responsible for the intimate connection between high and low-energy scale physics, and their key role in the mechanism of HTSC was conjectured very early on. More recently, the detection of quantum oscillations in high-magnetic field experiments on YBa2Cu3O6+x (YBCO) has suggested the existence of a Fermi surface of well-defined quasiparticles in underdoped cuprates, lending support to the alternative proposal that HTSC might emerge from a Fermi liquid across the whole cuprate phase diagram. Discriminating between these orthogonal scenarios hinges on the quantitative determination of the elusive quasiparticle weight Z, over a wide range of hole-doping p. By means of angle-resolved photoemission spectroscopy (ARPES) on in situ doped YBCO, and following the evolution of bilayer band-splitting, we show that the overdoped metal electronic structure (0.25<p<0.37) is in remarkable agreement with density functional theory and the Z=2p/(p+1) mean-field prediction. Below p~0.10-0.15, we observe the vanishing of the nodal quasiparticle weight Z_N; this marks a clear departure from Fermi liquid behaviour and -- consistent with dynamical mean-field theory -- is even a more rapid crossover to the Mott physics than expected for the doped resonating valence bond (RVB) spin liquid.
The surfaces generated by cleaving non-polar, two-dimensional oxides are often considered to be perfect or ideal. However, single particle spectroscopies on Sr2RuO4, an archetypal non-polar two dimensional oxide, show significant cleavage temperature
dependence. We demonstrate that this is not a consequence of the intrinsic characteristics of the surface: lattice parameters and symmetries, step heights, atom positions, or density of states. Instead, we find a marked increase in the density of defects at the mesoscopic scale with increased cleave temperature. The potential generality of these defects to oxide surfaces may have broad consequences to interfacial control and the interpretation of surface sensitive measurements.
