Zusammenfassung
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.
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