Probing the electronic structure of graphene near and far from the Fermi level via planar tunneling spectroscopy

TitleProbing the electronic structure of graphene near and far from the Fermi level via planar tunneling spectroscopy
Publication TypeJournal Article
Year of Publication2019
AuthorsDavenport, JL, Ge, Z, Liu, J, Nuñez-Lobato, C, Moon, S, Lu, Z, Quezada-Lopez, EA, Hellier, KL, LaBarre, PG, Taniguchi, T, Watanabe, K, Carter, SA, Ramirez, AP, Smirnov, D, Velasco, J
JournalApplied Physics Letters

Scanning tunneling spectroscopy (STS) has yielded significant insight into the electronic structure of graphene and other two-dimensional (2D) materials. STS directly measures a fundamental and directly calculable quantity: single particle density of states (SPDOS). Due to experimental setup limitations, however, STS has been unable to explore 2D materials in ultrahigh magnetic fields where electron-electron interactions can drastically change the SPDOS. Recent developments in the assembly of heterostructures composed of graphene and hexagonal boron nitride have enabled a device-based alternative to potentially overcome these roadblocks. Thus far, however, these nascent efforts are incomplete in analyzing and understanding tunneling spectra and have yet to explore graphene at high magnetic fields. Here, we report an experiment at magnetic fields up to 18 T, which uses graphene tunneling field effect transistors (TFETs) to establish a clear benchmark for the measurement and analysis of graphene planar tunneling spectroscopy. We acquire gate tunable tunneling spectra of graphene and then use these data and electrostatic arguments to develop a systematic analysis scheme. This analysis reveals that TFET devices directly probe electronic structure features near and far from the Fermi level. In particular, our study yields identification of the Dirac point and numerous Landau levels as they fill and empty with charge via the application of a gate voltage. Our work demonstrates that TFET devices are a viable platform for directly probing the electronic structure of graphene and other 2D materials in high magnetic fields, where exotic electronic states emerge.
We thank S. Tomarken for insightful discussions on tunneling spectroscopy and F. Joucken and Z. Schlesinger for helpful feedback. We also thank D. Lederman for providing the low temperature cryostat and cryostat operation expertise that facilitated data acquisition for this work.
J.V., Jr. acknowledges support from UCOP and from the Army Research Office under Contract No. W911NF-17-1-0473. K.W. and T.T. acknowledge support from the Elemental Strategy Initiative conducted by the MEXT, Japan, and the CREST (No. JPMJCR15F3), JST. A. P. Ramirez acknowledges support from the U.S. Department of Energy grant DE-SC0017862. A portion of this work was performed at the National High Magnetic Field Laboratory, which was supported by the National Science Foundation Cooperative Agreement No. DMR-1644779* and the State of Florida.