Finite conductivity minimum in bilayer graphene without charge inhomogeneities

Abstract

Boltzmann transport theory fails near the linear band crossing of single-layer graphene and near the quadratic band crossing of bilayer graphene. We report on a numerical study which assesses the role of interband coherence in transport when the Fermi level lies near the band-crossing energy of bilayer graphene. We find that interband coherence enhances conduction, and that it plays an essential role in bilayer graphene's minimum conductivity phenomena. This behavior is qualitatively captured by an approximate theory which treats interband coherence in a relaxation-time approximation. On the basis of this short-range-disorder model study, we conclude that electron-hole puddle formation is not a necessary condition for finite conductivity in bilayer graphene at zero average carrier density.

Quantum corrections in the Boltzmann conductivity of graphene and their sensitivity to the choice of formalism

“…The N = 2 case of (78) was worked out in collaboration with M. Trushin et al , see ref. [10]. The treatment in this section would until equation (75) is of order V r , r ≤ 4 it could in principle change the value or the order of the leading quantum correction.…”

“…The fourth conclusion is consistent with the recent paper ref. [10]. [68] We wish to stress that our electron-density-independent contribution ∼ ( k F ) 0 to the conductivity has a different origin than those discussed in previous studies [21,22].…”

The electronic properties of bilayer graphene

“…Transport characteristics and the nature of conductivity near the Dirac point were probed experimentally [2,3,8,19,20,[159][160][161][162] and investigated theoretically [163][164][165][166][167][168][169][170][171][172][173][174][175]. Neglecting trigonal warping, the minimal conductivity is predicted to be 8e 2 /(πh) [163,167,168], twice the value in monolayer graphene, while, in the presence of trigonal warping, it is larger, 24e 2 /(πh) [163,169], because of multiple Fermi surface pockets at low energy, section II E.…”

“…[176,177]. The characteristics of bilayer graphene in the presence of short-ranged defects and long-ranged chargedimpurities have been calculated [54,163,164,166,[171][172][173][174][175] and it is predicted that the conductivity has an approximately linear dependence on density at typical experimental densities [172]. At interfaces and potential barriers, conservation of the pseudospin degree of freedom may influence electronic transmission [178,179], as in monolayer graphene [178,180], including transmission at monolayer-bilayer interfaces [181][182][183][184], through multiple electrostatic barriers [185], or magnetic barriers [186,187].…”

Graphene conductivity near the charge neutral point

“…Thus, the puddle picture cannot be evoked in these cases, where it is likely that more general quantum phenomena play a relevant role in the transport process [15][16][17].…”