Anisotropic weakly localized transport in nitrogen-doped ultrananocrystalline diamond films

Abstract

We establish the dominant effect of anisotropic weak localization (WL) in three dimensions (3D) associated with a propagative Fermi surface on the conductivity correction in heavily nitrogen-doped ultrananocrystalline diamond (UNCD) films based on magnetoresistance 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 two-dimensional WL or strong localization regime. The corresponding dephasing time of electronic wave functions in these systems described as $\ensuremath{\sim}{T}^{\ensuremath{-}p}$ with $p<1$, follows a relatively weak temperature dependence compared to the generally expected nature for bulk dirty metals having $p\ensuremath{\ge}1$. The temperature dependence of Hall (electron) mobility together with an enhanced electron density has been used to interpret the unusual magnetotransport features and show delocalized electronic transport in these $n$-type UNCD films, which can be described as low-dimensional superlattice structures.