Physics (Internal)

The Coulomb problem in graphene and its connections with QED in strong fields

This event is part of the Biophysics/Condensed Matter Seminar Series.

Abstract: Charged (Coulomb) impurities play an important role in the transport characteristics of graphene samples. They can come from the environment, or selectively added through in ion beam irradiation. I will present the exact solution of the Dirac equation for massless and massive fermions on a Coulomb field. This solution entails the existence of a critical coupling separating two strikingly different regimes. Whereas the undercritical situation is essentially perturbative, for supercritical couplings highly non-perturbative effects appear, including strong hole (positron) resonances characteristic of the falling to the nucleus. This transition has important consequences for the screening and transport of these Dirac fermions, and leads to the emergence of a charged vacuum, in complete analogy with the problem of supercritical nuclei in QED. In particular, since the effective fine structure constant in graphene is close to unity, I will discuss how the effect can in principle be accessed experimentally with common impurities, through signatures in the conductivity, or local density of states.