First direct observation of Dirac fermions in graphite

TL;DR

This paper provides the first direct experimental evidence of massless Dirac fermions in graphite, revealing their coexistence with other quasiparticles and defect states, which enhances understanding of graphite's electronic properties.

Contribution

It reports the first direct observation of Dirac fermions in graphite, demonstrating their coexistence with parabolic quasiparticles and defect-induced states.

Findings

Direct observation of massless Dirac fermions in graphite.

Coexistence of Dirac fermions with parabolic quasiparticles.

Identification of defect-induced localized states.

Abstract

Originating from relativistic quantum field theory, Dirac fermions have been recently applied to study various peculiar phenomena in condensed matter physics, including the novel quantum Hall effect in graphene, magnetic field driven metal-insulator-like transition in graphite, superfluid in 3He, and the exotic pseudogap phase of high temperature superconductors. Although Dirac fermions are proposed to play a key role in these systems, so far direct experimental evidence of Dirac fermions has been limited. Here we report the first direct observation of massless Dirac fermions with linear dispersion near the Brillouin zone (BZ) corner H in graphite, coexisting with quasiparticles with parabolic dispersion near another BZ corner K. In addition, we report a large electron pocket which we attribute to defect-induced localized states. Thus, graphite presents a novel system where massless Dirac fermions, quasiparticles with finite effective mass, and defect states all contribute to the low energy electronic dynamics.