PORTLAND, Ore. -- The perfect crystalline structure of epitaxial graphene rearranges into a moire interference pattern of local band gaps when subjected to a magnetic field, according to researchers. The position-dependent atomic alignments between adjacent monolayers of graphene creates a regular pattern of regions where conduction is not allowed. The alignment could be magnetically switched in future carbon-based electronic devices.
"What we have discovered is a method to pattern the effective mass of graphene in an interesting way, with a magnetic switch to turn the pattern 'on' and 'off'," said Phillip First, a professor at Georgia Tech. "Whether it has practical consequences remains to be seen, but it's an essential piece of the puzzle which was both unexpected and unpredicted."
When magnetically switched on, electrons traveling though graphene must shuttle around "dead" regions, creating interference patterns that need to be well-understood if bi-layer graphene field-effect transistors are to be useful, according to First.
"Substrates or gate insulators that are lattice-matched to graphene such as boron nitride, could introduce 'ordered inhomogeneity' similar to what we observe," First added.
When subjected to a magnetic field, theory dictates that electrons in graphene travel in perfect cyclotronic orbits. But the researchers discovered that in practice isolated bandgaps on the surface created a regular patchwork of no-go areas for electrons. The mechanism is thought to be the slightly different lattice orientation of each layer, resulting in the moire pattern.
"Photonic devices such as far-infrared lasers might be made from transitions between the discrete energies of quantized cyclotron orbits," predicted First. "The new band gaps that we observe in this work could affect the performance of these photonic devices by introducing extra energy states."
Joseph Stroscio of the National Institute of Standards and Technology's Center for Nanoscale Science and Technology contributed to the research. .
Research funding was provided by the National Science Foundation, Semiconductor Research Corp., the W.M. Keck Foundation and Georgia Tech’s Materials Research Science and Engineering Center.