Graphene, a single-atom-thick layer of graphite, exhibits many phenomena characteristic of two-dimensional systems, such as the quantum Hall effect. But in addition to charge degrees of freedom, graphene also has the so-called spin and valley (jointly called flavor) degrees of freedom. Abanin et al. (p. 328; see the Perspective by Castro Neto) measured the nonlocal response of graphene samples close to the Dirac or neutrality point, where the charge carrier density tends to zero.
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