Time-dependent pair creation and the Schwinger mechanism in graphene

Abstract

The momentum spectrum of positively and negatively charged carriers created in intrinsic graphene submitted to a time-dependent external electric field is evaluated for many external field configurations. Owing to the formal analogy between relativistic quantum mechanics and the description of graphene quasiparticles in terms of the massless Dirac equation, the electron momentum density is evaluated within two-dimensional massless quantum electrodynamics coupled to a strong classical field. This allows the treatment of dynamical effects in electron-hole creation and gives a physical description in terms of the time-dependent Schwinger mechanism. At zero transverse momentum, it is shown that the Fermi bound in the electron-hole momentum spectrum is saturated in a certain momentum window and the pair density depends only on the potential difference between asymptotic potentials before and after the interaction. The pair density for nonzero transverse momenta is evaluated using numerical calculations. The numerical results demonstrate that an important number of pairs can be created by an external field through both tunneling and multiphoton processes. It is argued that these features of the dynamical pair production may facilitate the detection of the Schwinger mechanism using graphene as a condensed matter analog to quantum electrodynamics.

Schwinger mechanism revisited

“…Besides the production of elementary particles by external fields in vacuum, the Schwinger mechanism can also lead to the production of quasi-particle excitations in more exotic materials such as graphene [160][161][162][163][164], where it may be easier to achieve experimentally. The possibility of using ultracold atoms in an optical lattice as a simulator for the Schwinger mechanism was considered in ref.…”

Particle creation by peak electric field

“…Switch-ing the peak field on and off, we can imitate electric fields that are specific to condensed matter physics, in particular to graphene or Weyl semimetals as was reported, e.g., in Refs. [31][32][33][34][35][36][37][38][39].…”

Low-dimensional approach to pair production in an oscillating electric field: Application to bandgap graphene layers

“…Contrary to that, for smaller field strengths below E 3 × 10 4 V/cm, the pair density produced by an OEF is significantly larger than the CEF outcome. The reason is that in an OEF pairs can be generated both by the field amplitude but also by the time dependence of the field [36,37]; the latter channel is absent in a CEF. Accordingly, for ξ g < 1, the creation mechanism by multiphoton absorption can become dominant, leading to enhanced pair creation in an OEF as compared with a CEF.…”

“…It is reached when the interaction time with the external CEF approaches T sat ∼ p max /(eE). For larger interaction times, also particles with momenta exceeding p max are created which are not properly described by the Dirac equation [35,37].…”

“…The process was examined by methods of 2 + 1-dimensional QED in a constant electric background [29], 2 a Sauter-like field [35], and an electric field oscillating in time [36,37]. The lack of an energy gap at the K ± points in graphene implies, however, that the charge carriers behave like massless Dirac fermions.…”