Chiral tunneling and the Klein paradox in graphene

TL;DR

This paper demonstrates that the Klein paradox, a relativistic quantum phenomenon, can be experimentally observed in graphene, revealing unique tunneling behaviors of chiral quasiparticles in condensed matter systems.

Contribution

It proposes a simple condensed-matter experiment using graphene to test the Klein paradox, bridging high-energy physics concepts with material science.

Findings

Klein paradox can be tested in graphene-based systems.

Chiral quasiparticles exhibit highly anisotropic tunneling.

Massless and massive Dirac fermions show different tunneling behaviors.

Abstract

The so-called Klein paradox - unimpeded penetration of relativistic particles through high and wide potential barriers - is one of the most exotic and counterintuitive consequences of quantum electrodynamics (QED). The phenomenon is discussed in many contexts in particle, nuclear and astro- physics but direct tests of the Klein paradox using elementary particles have so far proved impossible. Here we show that the effect can be tested in a conceptually simple condensed-matter experiment by using electrostatic barriers in single- and bi-layer graphene. Due to the chiral nature of their quasiparticles, quantum tunneling in these materials becomes highly anisotropic, qualitatively different from the case of normal, nonrelativistic electrons. Massless Dirac fermions in graphene allow a close realization of Klein's gedanken experiment whereas massive chiral fermions in bilayer graphene offer an interesting complementary system that elucidates the basic physics involved.