Electronic transport properties of NbC(C)-C nanocomposites

Abstract

We report the electronic transport properties of a composite system comprising zero dimensional superconducting NbC(C) nanocapsules and carbon nanofiber matrix. DC susceptibility measurements of the nanocomposite indicate that the critical temperature $({T}_{\mathrm{C}})$ of NbC nanocrystals is $10.7\phantom{\rule{0.3em}{0ex}}\mathrm{K}$. The temperature dependence of electrical resistivity of the specimen pellet follows the Mott's ${T}^{\ensuremath{-}1∕4}$ law in a temperature range between ${T}_{\mathrm{C}}$ of NbC and $300\phantom{\rule{0.3em}{0ex}}\mathrm{K}$, owing to a strong degree of structural disorder in the carbon matrix. Below the ${T}_{\mathrm{C}}$ of NbC, when the change of its electrostatic energy $\ensuremath{\Delta}E$ is far greater than the thermal energy, an electron will be localized on an isolated NbC nanocrystal at very low temperatures, leading to ``Coulomb Blockade.'' As a result, a collective behavior of the single-electron tunneling effect takes place in a three-dimensional granular superconductors' network composed of the NbC/carbon/NbC tunneling junctions. The superconducting gap of NbC crystals is not found in the current-voltage curves, due to the suppression of surface superconductivity through the contact between NbC and carbon shells.