Doping-dependence of nodal quasiparticle properties in high-TcT_{\rm c} cuprates studied by laser-excited angle-resolved photoemission spectroscopy

We investigate the doping dependent low energy, low temperature ($T$ = 5 K) properties of nodal quasiparticles in the d-wave superconductor Bi$_{2.1}$Sr$_{1.9}$CaCu$_2$O$_{8+\delta}$ (Bi2212). By utilizing ultrahigh resolution laser-excited angle-resolved photoemission spectroscopy, we obtain precise band dispersions near $E_{F}$, mean free paths and scattering rates ($\Gamma$) of quasiparticles. For optimally and overdoped, we obtain very sharp quasiparticle peaks of 8 meV and 6 meV full-width at half-maximum, respectively, in accord with terahertz conductivity. For all doping levels, we find the energy-dependence of $\Gamma \sim |\omega |$, while $\Gamma$($\omega =0$) shows a monotonic increase from overdoping to underdoping. The doping dependence suggests the role of electronic inhomogeneity on the nodal quasiparticle scattering at low temperature (5 K \lsim 0.07T_{\rm c}), pronounced in the underdoped region

Local epitaxy of Ag on Bi2Sr2CaCu2O8+x(001)

Thin films of Ag have been deposited onto cleaved Bi2Sr2CaCu2O8+x(001) surfaces at room temperature. Ag 3d x-ray photoelectron diffraction experiments show very poor local order at coverages of up to 7 Å. For higher Ag coverages, a distinct diffraction pattern is forming, indicative of local epitaxy in the form of two domains of Ag(110) patches with one diagonal of the rectangular surface unit cell aligned along the substrate a axis. Comparison with previously published scanning-tunneling-microscopy results [Y. S. Luo et al., Phys. Rev. B 46, 1114 (1992)] leads us to the conclusion that Ag epitaxy is promoted by local disruption of the substrate upon initial Ag depositio

Angle-resolved photoemission experiments on Bi2Sr2CaCu2O8+?(001)

Core-level X-ray photoelectron-diffraction patterns have been measured from cleaved Bi2Sr2CaCu2O8+δ (001) surfaces for all elements present in this compound. The incommensurate modulation alongb ([010]) leads to a strong inequivalence ofa- andb-directions for Bi, Sr and Cu photoelectrons, while Ca and O emission show less effect. Ultraviolet-photoemission experiments recording the emission intensity at the Fermi energy over a large solid angle are also presented, providing a direct mapping of the Fermi surface. Ac(2×2) superstructure is observed on the Fermi surface suggesting antiferromagnetic correlations within the Cu−O planes. The effects of the lattice modulation are clearly observable at the Fermi energy, and they are enhanced for binding energies higher than a few tens of meV