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We report the fabrication of very smooth NdBCO thin films deposited by d.c. magnetron sputtering using Nd rich target (EDX composition Nd/sub 1.12/Ba/sub 1.88/Cu/sub 3/O/sub 7-/spl delta//). Films characterized by critical temperature (R=0) higher than 90 K and maximum roughness lower than 2-3 nm on large areas are routinely obtained on SrTiO/sub 3/ non-vicinal substrates. STM studies performed in situ in UHV environment, show a 2D nucleation mechanism of the growth preserved up to a thickness higher than 100 nm. This is in contrast to the common observation of screw dislocations starting from 10-12 nm in c-axis ReBCO thin films, that gives rise to an increase of the roughness with thickness. We compare the growth modes, the superconducting, and the structural properties of our NdBCO thin films deposited by d.c. magnetron sputtering from stoichiometric and Nd-rich targets, on different kind of substrates. The experimental results are discussed in the framework of the role of Nd/Ba substitution in the properties of Nd/sub 1+x/Ba/sub 2-x/Cu/sub 3/O/sub 7-/spl delta// thin films.

We probe the local quasiparticles density of states in micron-sized SmFeAsO(1-x)F(x) single crystals by means of scanning tunnelling spectroscopy. Spectral features resemble those of cuprates, particularly a dip-hump-like structure developed at energies larger than the gap that can be ascribed to the coupling of quasiparticles to a collective mode, quite likely a resonant spin mode. The energy of the collective mode revealed in our study decreases when the pairing strength increases. Our findings support spin-fluctuation-mediated pairing in pnictides.

We report the superconducting properties of Nd1+xBa2−xCu3O7−δ thin films deposited by dc magnetron sputtering from stoichiometric Nd1Ba2Cu3O7−δ and off-stoichiometric Nd1.12Ba1.88Cu3O7−δ targets. Highly epitaxial c-axis oriented samples with thicknesses ranging from 5 to 100 nm were obtained on SrTiO3(100) substrates from both targets. A suppression of screw-dislocation mediated growth for off-stoichiometric films is observed by STM, resulting in smooth surfaces with roughness of 2–3 nm on a 1 μm2 area. The effects of the deposition conditions on the structural and superconducting properties are investigated and discussed in relation to the Nd–Ba substitution in the Nd1+xBa2−xCu3O7−δ system.

By using scanning tunneling microscopy/spectroscopy we show that the interface between LaAlO3 and SrTiO3 band insulators is characterized by in-gap interface states. These features were observed in insulating as well as conducting LaAlO3/SrTiO3 bilayers. The data show how the interface density of states evolves across the insulating to metal transition, demonstrating that nanoscale electronic inhomogeneities in the system are induced by spatially localized electrons.

Scanning tunneling spectroscopy suggests the formation of a two dimensional electron gas (2DEG) on the TiO2 terminated surface of undoped SrTiO3 single crystals annealed at temperature lower than 400 {\deg}C in ultra high vacuum conditions. Low energy electron diffraction indicates that the 2D metallic SrTiO3 surface is not structurally reconstructed, suggesting that non-ordered oxygen vacancies created in the annealing process introduce carriers leading to an electronic reconstruction. The experimental results are interpreted in a frame of competition between oxygen diffusion from the bulk to the surface and oxygen loss from the surface itself., Comment: 9 pages, 3 figures, submitted to Physical Review B