Berkeley Lab Researchers Discover a Tiny Twist in Bilayer Graphene That May Solve a Mystery
August 12, 2013
Lynn Yarris (510) 486-5375 firstname.lastname@example.org
“Researchers with the U.S. Department of Energy (DOE)’s Lawrence Berkeley National Laboratory (Berkeley Lab) have discovered a unique new twist to the story of graphene, sheets of pure carbon just one atom thick, and in the process appear to have solved a mystery that has held back device development.
Electrons can race through graphene at nearly the speed of light – 100 times faster than they move through silicon. In addition to being superthin and superfast when it comes to conducting electrons, graphene is also superstrong and superflexible, making it a potential superstar material in the electronics and photonics fields, the basis for a host of devices, starting with ultrafast transistors. One big problem, however, has been that graphene’s electron conduction can’t be completely stopped, an essential requirement for on/off devices.
The Dirac spectrum of bilayer graphene when the two layers are exactly aligned (left) shifts with a slight interlayer twist that breaks interlayer-coupling and potential symmetry, leading to a new spectrum with surprisingly strong signatures in ARPES data. (Image courtesy of Keun Su Kim)
Working at Berkeley Lab’s Advanced Light Source (ALS), a DOE national user facility, a research team led by ALS scientist Aaron Bostwick has discovered that in the stacking of graphene monolayers subtle misalignments arise, creating an almost imperceptible twist in the final bilayer graphene. Tiny as it is – as small as 0.1 degree – this twist can lead to surprisingly strong changes in the bilayer graphene’s electronic properties.
Aaron Bostwick at Berkeley Lab’s Advanced Light Source led the discovery of a tiny twist in the formation of bilayer graphene that has a large impact on electronic properties. (Photo by Roy Kaltschmidt)
‘The introduction of the twist generates a completely new electronic structure in the bilayer graphene that produces massive and massless Dirac fermions,’ says Bostwick. ‘The massless Dirac fermion branch produced by this new structure prevents bilayer graphene from becoming fully insulating even under a very strong electric field. This explains why bilayer graphene has not lived up to theoretical predictions in actual devices that were based on perfect or untwisted bilayer graphene.’”
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A U.S. Department of Energy National Laboratory Operated by the University of California
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