Despite recent advances in understanding high-transition-temperature (high-T(c)) superconductors, there is no consensus on the origin of the superconducting 'glue': that is, the mediator that binds electrons into superconducting pairs. The main contenders are lattice vibrations (phonons) and spin-excitations, with the additional possibility of pairing without mediators. In conventional superconductors, phonon-mediated pairing was unequivocally established by data from tunnelling experiments. Proponents of phonons as the high-T(c) glue were therefore encouraged by the recent scanning tunnelling microscopy experiments on hole-doped Bi2Sr2CaCu2O8-delta (BSCCO) that reveal an oxygen lattice vibrational mode whose energy is anticorrelated with the superconducting gap energy scale. Here we report high-resolution scanning tunnelling microscopy measurements of the electron-doped high-T(c) superconductor Pr0.88LaCe0.12CuO4 (PLCCO) (T(c) = 24 K) that reveal a bosonic excitation (mode) at energies of 10.5 +/- 2.5 meV. This energy is consistent with both spin-excitations in PLCCO measured by inelastic neutron scattering (resonance mode) and a low-energy acoustic phonon mode, but differs substantially from the oxygen vibrational mode identified in BSCCO. Our analysis of the variation of the local mode energy and intensity with the local gap energy scale indicates an electronic origin of the mode consistent with spin-excitations rather than phonons.

Gram quantities of titania (TiO 2) nanotubes, with a typical outside diameter about 9 nm, wall thickness of about 2.5 nm, and length of about 600 nm, were synthesized from anatase nanopowder and micropowder using the hydrothermal method. The crystallization, structure, and phase stability of the nanotubes at high temperatures were studied. A morphology change from nanotube to nanowire was observed at 650 • C. The as-prepared nanotubes were usually contaminated with sodium impurities and were poorly crystallized, but under optimized synthesis conditions the impurity phase was completely removed, resulting in highly crystallized nanotubes. The volume filling fraction of the autoclave as well as the concentration of the acid treatment were found to be particularly important for controlling the purity and crystallinity of the resulting nanotubes. The various TiO 2-derived nanotube phases (sodium titanate and hydrogen titanate) reported previously by different groups were also observed under different synthesis conditions, resolving the contradiction among the previous results.

High-temperature (high-T c ) superconductivity in the copper oxides arises from electron or hole doping of their antiferromagnetic (AF) insulating parent compounds. The evolution of the AF phase with doping and its spatial coexistence with superconductivity are governed by the nature of charge and spin correlations and provide clues to the mechanism of high-T c superconductivity. Here we use a combined neutron scattering and scanning tunneling spectroscopy (STS) to study the T c evolution of electron-doped superconducting Pr 0.88 LaCe 0.12 CuO 4- obtained through the oxygen annealing process. We find that spin excitations detected by neutron scattering have two distinct modes that evolve with T c in a remarkably similar fashion to the electron tunneling modes in STS. These results demonstrate that antiferromagnetism and superconductivity compete locally and coexist spatially on nanometer length scales, and the dominant electron-boson coupling at low energies originates from the electron-spin excitations.High-temperature (high-T c ) superconductivity in the copper oxides arises from electron or hole doping of their antiferromagnetic (AF) insulating parent compounds 1,2 . The evolution of the AF phase with doping and its spatial coexistence with superconductivity are governed by the nature of charge and spin correlations and provide clues to the mechanism of high-T c superconductivity 3,4 . Electron correlation in hole-and electrondoped materials can be quite different 5 . While doped electrons reside in the Cu 3d orbitals with correlations involving primarily d-electrons 2 , doped holes form Zhang-Rice singlets moving in the background of Cu spins 1 and are subject to stronger correlations 1-7 . In electron-doped copper oxides, there are bulk signatures of coexisting AF and superconducting phases [8][9][10][11][12] . These measurements, however, cannot distinguish nanoscale spatial coexistence from larger scale phase segregation. Here we report advances made by a combined neutron scattering and scanning tunneling spectroscopy (STS) studies on nominally identical electron-doped superconducting Pr 0.88 LaCe 0.12 CuO 4- (PLCCO) samples with different T c 's obtained through the oxygen annealing process 13,14 . We find that spin excitations detected by neutron scattering 15,16 have two distinct modes that evolve with T c in a remarkably similar fashion to the electron tunneling modes 17 in STS. Spatial mapping of the modes shows nanoscale regions of coexisting AF and superconducting order in the lower T c samples. Since the annealing process is not expected to change lattice (phonon) properties 2,13,14,18 , these results demonstrate that antiferromagnetism and superconductivity compete locally and coexist spatially on nanometer length scales, and the dominant electron-boson coupling at low energies originates from the electron-spin excitations 17 rather than electron-phonon interactions 19 .There is experimental and theoretical evidence suggesting that antiferromagnetism is a competing phase to superconductivity i...

We report a simple low-temperature inverse micelle solvothermal route for the synthesis of a large quantity of single-crystalline germanium nanocrystals. X-ray diffraction measurement indicates that the as-prepared nanocrystals are composed of pure Ge with a cubic structure. The morphology, size, chemical composition, crystallinity, and structural features of the as-prepared nanocrystals were characterized by transmission electron microscopy and energy-dispersive x-ray spectroscopy.