Large negative magnetoresistance and strong localization in highly disordered electrospun pregraphitic carbon nanofiber

A highly disordered pregraphitic carbon nanofiber with the product of its quasi-Fermi wave vector and mean free path close to 1 was fabricated using electrospinning technique. Strong localization made the conductivity vary with temperature as σ [proportional to]Τ-1/2 from 300 to 5 K, suggesting variable range hopping as the conductivity mechanism, and resulted in a large negative magnetoresistance from 300 K down to 1.9 K that can still be quantitatively described using weak localization and electron interaction models. Comments Postprint version. Published in Applied Physics Letters, Volume 89, Issue 12, Article 123119, September 2006, 3 pages. Publisher URL: http://dx.doi.org/10.1063/1.2338573 This journal article is available at ScholarlyCommons: http://repository.upenn.edu/ese_papers/212 Large negative magnetoresistance and strong localization in highly disordered electrospun pregraphitic carbon nanofiber Yu Wang and Jorge J. Santiago-Avilés Department of Electrical and Systems Engineering, University of Pennsylvania, 200 South 33rd Street, Philadelphia, Pennsylvania 19104 Received 24 March 2006; accepted 18 July 2006; published online 21 September 2006 A highly disordered pregraphitic carbon nanofiber with the product of its quasi-Fermi wave vector and mean free path close to 1 was fabricated using electrospinning technique. Strong localization made the conductivity vary with temperature as ln T−1/2 from 300 to 5 K, suggesting variable range hopping as the conductivity mechanism, and resulted in a large negative magnetoresistance from 300 K down to 1.9 K that can still be quantitatively described using weak localization and electron interaction models. © 2006 American Institute of Physics. DOI: 10.1063/1.2338573 Disorder in electronic system is known to produce nonperiodic Anderson potentials. For weak disorder and small Anderson potential, their effect is to introduce a finite mean free path l. For strong disorder and Anderson potential, however, the electron is localized. Localization not only severely shortens the mean free path, but also gives rise to mobility edge Ec in the conduction band. 1,2 The product kFl, where kF is the quasi-Fermi wave vector, reflects the degree of the disorder and localization. For kFl 1 disorder and localization are weak, quasi-Fermi level EF is close to Ec, and localized electrons can be thermally activated to the conducting band higher than Ec, where they can move by diffusion. Scaling theory predicts the logarithmic relation