Nonequilibrium excitations and transport of Dirac electrons in electric-field-driven graphene

Abstract

We investigate nonequilibrium excitations and charge transport in charge-neutral graphene driven with dc electric field by using the nonequilibrium Green's function technique. Due to the vanishing Fermi surface, electrons are subject to non-trivial nonequilibrium excitations such as highly anisotropic momentum distribution of electron-hole pairs, an analog of the Schwinger effect. We show that the electron-hole excitations, initiated by the Landau-Zener tunneling with a superlinear IV relation I ∝ E 3/2 , reaches a steady state dominated by the dissipation due to optical phonons, resulting in a marginally sublinear IV with I ∝ E, in agreement with recent experiments. The linear IV starts to show the sign of current saturation as the graphene is doped away from the Dirac point, and recovers the semi-classical relation for the saturated velocity. We give a detailed discussion on the nonequilibrium charge creation and the relation between the electron-phonon scattering rate and the electric field in the steady-state limit. We explain how the apparent Ohmic IV is recovered near the Dirac point. We propose a mechanism where the peculiar nonequilibrium electron-hole creation can be utilized in an infra-red device.

Impact of nuclear vibrations on van der Waals and Casimir interactions at zero and finite temperature

“…Macroscopic treatments of vdW or Casimir interactions involving graphene rely on continuum models of its optical susceptibility, which enter into the familiar Lifshitz formula as idealized reflection coefficients of perfectly thin sheets [1]. These models typically start with quantum-mechanical tightbinding Hamiltonian for the localized π-bonding orbitals [40][41][42][43][44][45], while neglecting contributions from phonons to the material response and dissipation (though such contributions can be mitigated quantum mechanically through the addition of appropriate coupling [64] and reservoir [60] potentials.) This quantum-mechanical tight-binding electronic Hamiltonian is also commonly approximated as having linear dispersion around the Dirac points, in which case the susceptibility is derived as the lowest-order linear response to an applied perturbative electric field, consistent with the random-phase approximation (RPA).…”

“…Additionally, compared to the fullerene or carbyne wire, we expect graphene to have more channels for dissipation in its response. However, in undoped graphene, the dissipation rates due to electron-electron or electron-acoustic phonon scattering typically do not exceed 10 12 rad/s [60]. For computational convenience, we employ a somewhat larger dissipation rate of 10 13 rad/s, encoded in B I .…”

Observation of Anomalous Non-Ohmic Transport in Current-Driven Nanostructures

“…Electrons and/or phonons may also form a nonequilibrium distribution within the respective subsystem, which cannot be characterized by an effective temperature [19][20][21]. Significant progress has been recently achieved in the understanding of nonequilibrium states of electrons and phonons at nanoscale [22][23][24][25][26]. However, a comprehensive microscopic understanding of current-induced thermal energy generation and transport has not yet emerged.…”

Non-equilibrium Effects in Dissipative Strongly Correlated Systems

“…The results discussed in this chapter are directly comparable to experimental data. For further details, we refer the reader to the publication [66].…”