A research team led by physicists at the University of California, Riverside has identified a property of "bilayer graphene" (BLG) that the researchers say is analogous to finding the Higgs boson in particle physics.
Graphene, nature's thinnest elastic material, is a one-atom thick sheet of carbon atoms arranged in a hexagonal lattice. Because of graphene's planar and chicken wire-like structure, sheets of it lend themselves well to stacking.
BLG is formed when two graphene sheets are stacked in a special manner. Like graphene, BLG has high current-carrying capacity, also known as high electron conductivity. The high current-carrying capacity results from the extremely high velocities that electrons can acquire in a graphene sheet.
The physicists report that in investigating BLG's properties they found that when the number of electrons on the BLG sheet is close to 0, the material becomes insulating (that is, it resists flow of electrical current) -- a finding that has implications for the use of graphene as an electronic material in the semiconductor and electronics industries.
BLG becomes insulating because its electrons spontaneously organize themselves when their number is small. Instead of moving around randomly, the electrons move in an orderly fashion. This is called 'spontaneous symmetry breaking' in physics.
An important finding of the research team is that the intrinsic "energy gap" in BLG grows with increasing magnetic field.
In solid state physics, an energy gap (or band gap) refers to an energy range in a solid where no electron states can exist. Generally, the size of the energy gap of a material determines whether it is a metal (no gap), semiconductor (small gap) or insulator (large gap). The presence of an energy gap in silicon is critical to the semiconductor industry since, for digital applications, engineers need to turn the device 'on' or conductive, and 'off' or insulating.
Single layer graphene (SLG) is gapless, however, and cannot be completely turned off because regardless of the number of electrons on SLG, it always remains metallic and a conductor. BLG, on the other hand, can in fact be turned off. But the band gap is still too small for practical applications. Scientists say that trilayer graphene and tetralayer graphene have much larger energy gaps that can be used for digital and infrared technologies. They already have begun working with these materials.
