3 research outputs found
Anisotropic weakly localized transport in nitrogen-doped ultrananocrystalline diamond films
We establish the dominant effect of anisotropic weak localization (WL) in
three dimensions associated with a propagative Fermi surface, on the
conductivity correction in heavily nitrogen doped ultrananocrystalline diamond
(UNCD) films based on magneto-resistance studies at low temperatures. Also, low
temperature electrical conductivity can show weakly localized transport in 3D
combined with the effect of electron-electron interactions in these materials,
which is remarkably different from the conductivity in 2DWL or strong
localization regime. The corresponding dephasing time of electronic
wavefunctions in these systems described as ~ T^-p with p < 1, follows a
relatively weak temperature dependence compared to the generally expected
nature for bulk dirty metals having . The temperature dependence of
Hall (electron) mobility together with an enhanced electron density has been
used to interpret the unusual magneto-transport features and show delocalized
electronic transport in these n-type UNCD films, which can be described as
low-dimensional superlattice structures.Comment: 27 pages, 6 figures, To be published in Physical Review
Degradation behavior of MgB<SUB>2</SUB> superconductor
The degradation behavior of polycrystalline MgB2 superconductor, exposed to water and ambient atmosphere, has been studied. We have found that prolonged exposure to water completely destroys superconductivity. Optical microscopic and X-ray diffraction analyses indicate that, on exposure to water, the material becomes amorphous like. X-ray photoelectron spectroscopic measurements reveal the strongly hygroscopic character of MgB2 and we have found that, even at room temperature, water and air change it into Mg(OH)2, MgCO3 and B2O3