doi:10.1038/nindia.2012.172 Published online 26 November 2012
Researchers have discovered unique signatures of conductivity fluctuations in single-layer graphene when exposed to extremely tiny electric and magnetic fields at very low temperature. This property of graphene could be exploited to make a generation of efficient memory devices, field-effect low-power transistors and even components of quantum computers.
Graphene, a one-atom thick sheet of carbon atoms arranged in a honeycomb lattice, is a unique crystal. In graphene, conduction and valence bands cross the Fermi level, the energy level that separates both the band structures, at two points leading to formation of two valleys. Like the spin of electrons, valleys are electron states in the band structure of graphene.
Although universal conductivity fluctuations (UCF) in low-temperature electrical transport in nanosized graphene have been reported, no studies have investigated the effects of valleys on UCF in graphene.
To pin down the influence of valleys on UCF, the researchers laid monolayer graphene over a silicon oxide wafer. They then exposed the monolayer graphene to tiny electric and magnetic fields at temperatures within a fraction of a degree from absolute zero.
The study found that nanoscale conductivity fluctuations weakened with increasing temperature, and valleys contributed to such fluctuations. The fluctuations were universal and unique across the entire monolayer grapheme, irrespective of geometry, charge carrier mobility and temperature.
"Unlike spin, valley information is extremely hard to detect, and this experiment shows a novel way to do so using conductivity fluctuations," says lead researcher Arindam Ghosh. Such behavior of monolayer graphene based on the influence of valleys on UCF may spawn valleytronics, a new realm of electronics similar to spintronics relying on the spin of electrons, he adds.