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Abstract: Considering the magnetotransport data obtained on nanocrystalline variety of heavily boron-doped diamond films prepared by plasma-enhanced chemical vapour deposition technique, we have proposed a new model of unconventional superconductivity observed in this material (T C =1.66 K) which is based on the very experimental fact that symptoms of localization are precursors to the on-set of superconductivity. It is shown that the system treated as disordered Mott''s metal in which the low-temperature transport is controlled by weak localization of carriers should reveal, in the Kelvin range, superconducting transition just when the holes occupying neighbouring weakly localized orbits are paired by means of spin-flip mechanism. Besides, close analogy between properties of a hole on weakly localized orbit and vortex in a classical type-II superconductor is suggested. [Copyright &y& Elsevier]

A method for mapping the surface conductivity of hydrogen-terminated (H-terminated) diamond on a sub-100 nm scale is presented. The measuring technique relies on electrostatic force microscopy imaging of the voltage distribution of a current-carrying H-terminated diamond film. The uniform linear voltage drop in highly conductive H-terminated diamond surface layers indicates that the layers behave as homogeneous, diffusive conductors with a well-defined value of the sheet resistance. On the other hand, we observe conductive as well as insulating regions that coexist for not perfectly H-terminated diamond surfaces with poor electric conductivity. [ABSTRACT FROM AUTHOR]

In this letter we present results of magnetotransport measurements, carried out on heavily nitrogen-doped ultrananocrystalline diamond films, prepared by plasma-enhanced chemical vapor deposition. This material having at room temperature appreciably high electric conductivity (∼4200 S m-1) revealed surprisingly at Kelvin temperatures a giant negative magnetoresistance reaching up to 22% at 1.28 K and at 8 T. The analysis of experimental data has borne evidence of the fact that the transport in this subsystem has a character of low-dimensional disordered metal and it is controlled by quantum interference effects of electrons resulting in their weak localization. [ABSTRACT FROM AUTHOR]

Abstract: Analyzing the magnetotransport data obtained on nanocrystalline variety of heavily boron-doped diamond, we have proposed a new model of unconventional superconductivity in this material based on the very experimental fact that the symptoms of localization are precursors of superconducting transition. It is shown by quantitative arguments that the system treated as disordered Mott''s metal in which the transport is controlled by weak localization of carriers should reveal, in the Kelvin range, superconducting transition just when the holes occupying neighbouring weakly localized orbits are paired by means of a spin-flip mechanism. [Copyright &y& Elsevier]

Abstract: Photocurrent measurements on phosphorous-doped n-type diamond have been performed at liquid helium temperature and varying electric field. For increasing fields the onset of the experimental photocurrent versus photon energy shifts towards smaller photon energy. At relative small hν its slope is nearly constant, although smooth structures can be observed in the spectrum. These and other observations at low photon energy are interpreted using an impurity-assisted tunnelling model. The idea behind this model is that, at finite electric fields, the impurity electron tunnels a few times towards neighbouring neutral impurity atoms, until it arrives in a non-localized conduction band state and contributes to the photocurrent. The experimental results could be explained in a semi-quantitative way. The consequences for various experimental circumstances (varying field, temperature, photon energy, impurity concentration) are discussed. [Copyright &y& Elsevier]