Conductance enhancement due to atomic potential fluctuations in graphene (original) (raw)
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Electronic transport in two dimensional graphene
2010
We provide a broad review of fundamental electronic properties of two-dimensional graphene with the emphasis on density and temperature dependent carrier transport in doped or gated graphene structures. A salient feature of our review is a critical comparison between carrier transport in graphene and in two-dimensional semiconductor systems (e.g. heterostructures, quantum wells, inversion layers) so that the unique features of graphene electronic properties arising from its gap- less, massless, chiral Dirac spectrum are highlighted. Experiment and theory as well as quantum and semi-classical transport are discussed in a synergistic manner in order to provide a unified and comprehensive perspective. Although the emphasis of the review is on those aspects of graphene transport where reasonable consensus exists in the literature, open questions are discussed as well. Various physical mechanisms controlling transport are described in depth including long- range charged impurity scattering, screening, short-range defect scattering, phonon scattering, many-body effects, Klein tunneling, minimum conductivity at the Dirac point, electron-hole puddle formation, p-n junctions, localization, percolation, quantum-classical crossover, midgap states, quantum Hall effects, and other phenomena.
Journal of Applied Physics, 2008
Motivated by recent studies on the use of graphene for new concepts of electronic/spintronic devices, the authors develop an efficient calculation method based on the nonequilibrium Green's function to solve the quantum relativisticlike Dirac's equation that governs the low-energy excited states in graphene. The approach is then applied to investigate the electronic transport and the spin polarization in a single-graphene barrier structure. The obtained results are presented and analyzed in detail aiming to highlight typical properties of the considered graphene structure as well as the efficiency of the developed approach that both may be helpful for further development in electronic devices and in spintronics.
Spin-Orbit Interaction and Isotropic Electronic Transport in Graphene
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Broken symmetries in graphene affect the massless nature of its charge carriers. We present an analysis of scattering by defects in graphene in the presence of spin-orbit interactions (SOIs). A characteristic constant ratio ( 2) of the transport to elastic times for massless electrons signals the anisotropy of the scattering. We show that SOIs lead to a drastic decrease of this ratio, especially at low carrier concentrations, while the scattering becomes increasingly isotropic. As the strength of the SOI determines the energy (carrier concentration) where this drop is more evident, this effect could help evaluate these interactions through transport measurements.
Quantum transport of Dirac fermions in graphene nanostructures
2010 14th International Workshop on Computational Electronics, 2010
An effective approach of quantum transport of Dirac carriers in mono-and bi-layer graphene structures and devices is presented. Initially based on the Green's function formalism to treat the Dirac Hamiltonian of massless particles in twodimensional mono-layer graphene, the model has been extended to to small bandgap materials and to bi-layer graphene with massive carriers. It is applied to investigate some transport problems as the minimum conductivity, the tunneling properties the spin-polarized transport through single-barrier structures, and the operation of graphene field-effect transistors.
General Scattering Mechanism and Transport in Graphene
2011
Using quasi-time dependent semi-classical transport theory in RTA, we obtained coupled current equations in the presence of time varying field and based on general scattering mechanism τ ∝ E β. We find that close to the Dirac point, the characteristic exponent β = +2 corresponds to acoustic phonon scattering. β = +1 long-range Coulomb scattering mechanism. β = −1 is short-range delta potential scattering in which the conductivity is constant of temperature. The β = 0 case is ballistic limit. In the low energy dynamics of Dirac electrons in graphene, the effect of the time-dependent electric field is to alter just the electron charge by e → e(1 + (Ωτ) 2) making electronic conductivity non-linear. The effect of magnetic filed is also considered.
Graphene: New bridge between condensed matter physics and quantum electrodynamics
Solid State Communications, 2007
Graphene is the first example of truly two-dimensional crystals-it's just one layer of carbon atoms. It turns out to be a gapless semiconductor with unique electronic properties resulting from the fact that charge carriers in graphene demonstrate charge-conjugation symmetry between electrons and holes and possess an internal degree of freedom similar to "chirality" for ultrarelativistic elementary particles. It provides unexpected bridge between condensed matter physics and quantum electrodynamics (QED). In particular, the relativistic Zitterbewegung leads to the minimum conductivity of order of conductance quantum e 2 /h in the limit of zero doping; the concept of Klein paradox (tunneling of relativistic particles) provides an essential insight into electron propagation through potential barriers; vacuum polarization around charge impurities is essential for understanding of high electron mobility in graphene; index theorem explains anomalous quantum Hall effect.
Theory of the electronic and transport properties of epitaxial graphene
2011
We discuss the novel electronic properties of graphene under an external periodic scalar or vector potential, and the analytical and numerical methods used to investigate them. When graphene is subjected to a one-dimensional periodic scalar potential, owing to the linear dispersion and the chiral (pseudospin) nature of the electronic states, the group velocity of its carriers is renormalized highly anisotropically in such a manner that the velocity is invariant along the periodic direction but is reduced the most along the perpendicular direction. Under a periodic scalar potential, new massless Dirac fermions are generated at the supercell Brillouin zone boundaries. Also, we show that if the strength of the applied scalar potential is sufficiently strong, new zero-energy modes may be generated. With the periodic scalar potential satisfying some special conditions, the energy dispersion near the Dirac point becomes quasi one-dimensional. On the other hand, for graphene under a one-dimensional periodic vector potential (resulting in a periodic magnetic field perpendicular to the graphene plane), the group velocity is reduced isotropically and monotonically with the strength of the potential.
Charge Transport in Chemically Doped 2D Graphene
Physical Review Letters, 2008
We report on a numerical study of electronic transport in chemically doped 2D graphene materials. By using ab initio calculations, a self-consistent scattering potential is derived for boron and nitrogen substitutions, and a fully quantum-mechanical Kubo-Greenwood approach is used to evaluate the resulting charge mobilities and conductivities of systems with impurity concentration ranging within [0.5, 4.0]%. Even for a doping concentration as large as 4.0%, the conduction is marginally affected by quantum interference effects, preserving therefore remarkable transport properties, even down to the zero temperature limit. As a result of the chemical doping, electron-hole mobilities and conductivities are shown to become asymmetric with respect to the Dirac point.