Lene Gammelgaard: Lithographic band structure engineering of graphene

posted 27 May 2019, 11:56 by info admin   [ updated 12 Aug 2019, 02:26 ]
Lene Gammelgaard, Bjarke Sørensen Jessen, Peter Bøggild,  Department of Physics, Technical University of Denmark, Kongens Lyngby, Denmark

Two-dimensional materials such as graphene allow direct access to the entirety of atoms constituting the crystal. While this makes lithographic shaping particularly attractive as a tool for band structure engineering through quantum confinement effects, edge disorder and contamination have so far limited progress towards experimental realization. We demonstrate here band structure engineering by direct, ultra-dense lithographic patterning of graphene [1]. Specifically, we have fabricated a triangular superlattice of etched holes with a period of 35 nm and a separation of 12-15 nm in a graphene sheet encapsulated in hexagonal boron nitride. We observe a distinct magnetotransport regime in the nanostructured graphene, with a nonlinear Landau level fan; in contrast to pristine graphene, and a band gap of 156 meV, which can be tuned with an external magnetic field. The rich magnetotransport measurements are accurately described by both tight-binding simulations and an analytical model based on Dirac fermions in ring geometries [2]. Furthermore, we observe strong indications that the lithographically engineered band structure at the main Dirac point is cloned to a satellite peak that appears due to moiré interactions between the graphene and the encapsulating hexagonal boron nitride. Band structure design in two-dimensional materials by top-down patterning enables the exploration of many exciting predictions and opportunities such as valleytronics [2] and spin qubits [3], as well as potential platform for “twistronic” circuits.

[1] B. S. Jessen, L. Gammelgaard, et al., Nat. Nano. 14, 340-346, (2019)
[2] M. R. Thomsen, et al., Phys. Rev. B, 95, 235427, (2017)
[3] T. G. Pedersen et al. Phys. Rev. Lett, 473,136804, (2008)

Lene Gammelgaard obtained her PhD in experimental physics at the Technical University of Denmark (DTU) in 2016 with the title “2D Material Device Architectures: Process Optimization and Characterization”. She is currently a postdoctoral researcher in the group of Prof. Peter Bøggild at DTU Physics. Her interests are physics and fabrication of nanodevices, including stacking of van der Waals heterostructures, cleanroom fabrication of devices by shaping and electrical contacting, and fabrication of dense nano-structures by electron beam lithography.