Observation of Landau levels of Dirac fermions in graphite

TL;DR

This paper reports the direct observation of Landau levels of Dirac fermions in graphite using scanning tunnelling spectroscopy, revealing coexistence of massless and massive Dirac fermions and their unique quantum-relativistic properties.

Contribution

First direct detection of Landau levels of Dirac fermions in bulk graphite, demonstrating 2D quantum-relativistic behavior in a 3D material.

Findings

Observation of Landau levels in graphite up to 12 Tesla

Evidence of coexistence of massless and massive Dirac fermions

Identification of zero-energy Landau level as a hallmark of Dirac fermions

Abstract

The low energy electronic excitations in single layer and bilayer graphite (graphene) resemble quantum-relativistic particles also known as Dirac Fermions (DF). They possess an internal degree of freedom, chirality, that leads to unusual Landau Level (LL) energy sequences in a magnetic field and profoundly alters the magneto-transport properties. One of the consequences is an anomalous Quantum-Hall effect, recently detected in both single layer and bi-layer graphene. However the underlying cause, the unusual LL sequence, was never observed. Here we report the direct observation of LL of DF by means of low temperature Scanning-Tunnelling-Spectroscopy (STS) on the surface of graphite in fields up to 12 Tesla. We find evidence of coexistence of massless and massive DF, and identify the zero-energy LL which is a unique consequence of their quantum-relativistic nature. Surprisingly these strictly two-dimensional properties emerge even on bulk graphite in samples where the interlayer coupling is weak.