Observing the Quantization of Zero Mass Carriers in Graphene

• Published in: Science (American Association for the Advancement of Science) Vol. 324; no. 5929; pp. 924 - 927
• Main Authors: Miller, David L, Kubista, Kevin D, Rutter, Gregory M, Ruan, Ming, de Heer, Walt A, First, Phillip N, Stroscio, Joseph A
• Format: Journal Article
• Language: English
• Published: Washington, DC American Association for the Advancement of Science 15.05.2009; The American Association for the Advancement of Science
• Subjects: Atoms & subatomic particles; Carbon; Charge carriers; Condensed matter: electronic structure, electrical, magnetic, and optical properties; Electronic structure and electrical properties of surfaces, interfaces, thin films and low-dimensional structures; Electronic transport in multilayers, nanoscale materials and structures; Electrons; Energy; Exact sciences and technology; Graphene; Graphite; Line spectra; Magnetic fields; Magnetic spectroscopy; Materials science; Physics; Quantum physics; Sampling bias; Spectral index; Magnetooscillatory properties; Graphene; Tunnel effect; Magnetic field effects; Electron hole pair; Landau levels; Massless particles; Magnetoresistance
• ISSN: 0036-8075; 1095-9203
• DOI: 10.1126/science.1171810

Application of a magnetic field to conductors causes the charge carriers to circulate in cyclotron orbits with quantized energies called Landau levels (LLs). These are equally spaced in normal metals and two-dimensional electron gases. In graphene, however, the charge carrier velocity is independent of their energy (like massless photons). Consequently, the LL energies are not equally spaced and include a characteristic zero-energy state (the n = 0 LL). With the use of scanning tunneling spectroscopy of graphene grown on silicon carbide, we directly observed the discrete, non-equally-spaced energy-level spectrum of LLs, including the hallmark zero-energy state of graphene. We also detected characteristic magneto-oscillations in the tunneling conductance and mapped the electrostatic potential of graphene by measuring spatial variations in the energy of the n = 0 LL.