Studies of the magnetotransport of strongly interacting 2D holes in high mobility, gated, GaAs quantum wells have been carried out a very low temperatures to search for possible anisotropy in the field-induced re-entrant insulating phase. The latter phase was observed in the resistivity at a magnetic field that depended on hole density but that was independent of current direction. This shows that the re-entrant insulating phase is not due to a proposed anisotropic stripe order, but is instead caused by Wigner crystallization.
New physics has had to be invoked to explain the existence of exotic quantum Hall states such as the n =5/2 and 7/2 states. Recent progress in fabrication of high-quality low-density samples allows one to probe these states in a new regime where the electron-electron interactions are strong. The results reveal the existence of anisotropic transport for n = 7/2 in a high-quality very dilute 2D electron system. The new behavior is attributed to a large Landau level mixing effect that perturbs the pairing stability of composite fermions in the dilute limit.
A layer of graphite one atom thick holds great promise for the future of microelectronics. It's called graphene, and University of Manchester physicists Andre Geim and Kostya Novoselov this week won a 2010 Nobel Prize for creating it.
"It's thrilling when scientists affiliated in some way with the Mag Lab receive such a well-deserved honor," said Greg Boebinger, director of the National High Magnetic Field Laboratory. Boebinger co-authored a landmark 2007 Science paper, "Room-Temperature Quantum Hall Effect in Graphene," with the Nobel laureates.
"What started as a small but exciting development has evolved into a major research effort," said Boebinger, noting that 17 different user groups studied graphene at the Magnet Lab in 2009, and that interest in the material shows no signs of abating.
Geim and Novoselov famously created graphene using a simple "Scotch tape" technique — humble beginnings for a material that could transform computers, cell phones, and other technologies. They placed a piece of tape on some graphite and pulled it off. When they examined the material trace with a microscope, they were able to find flecks that were only one layer of atoms thick.
Graphene is a hexagonal array of carbon atoms so thin it's virtually see-through. It has remarkable electronic and mechanical properties, and is as good a conductor of electricity as copper and is stronger than steel. Because of its amazing properties, some scientists speculate that graphene could one day replace silicon as the principal component in semiconductor devices, leading to smaller, faster and more versatile electronic devices.
But as with so many things in science, there's still a lot to learn about graphene before the engineers start using it for practical purposes. The race for answers has placed the material at the intellectual frontier of condensed matter physics, which means increased demand for magnet time at the Mag Lab. Of the 17 user groups researching graphene in 2009, six of the groups consisted of new users, and between the lab's DC Field and Pulsed Magnet user programs, that number is expected to grow larger still.
"Graphene is a fascinating material for about 20 different reasons, but to a lot of physicists, the most interesting thing about it is what happens to it when it's put in a magnetic field," said Paul Cadden-Zimansky, a postdoctoral associate who splits his time between the Magnet Lab and Columbia University. "The higher the field, the more interesting it gets."
Driving that point home, Pulsed Field Facility user Layla Booshehri from Professor Jun Kono research group Rice University recently collaborated with Pulsed Field Facility Director Chuck Mielke to probe single-layer graphene at fields up to 170 tesla using the lab's single-turn magnet. The magneto absorption measurements reveal a wavelength-dependent resonance at high magnetic fields, allowing the researchers to pinpoint the Fermi energy of the doped graphene.
The National High Magnetic Field Laboratory develops and operates state-of-the-art, high-magnetic-field facilities that faculty and visiting scientists and engineers use for research. The laboratory is sponsored by the National Science Foundation and the state of Florida. To learn more visit www.magnet.fsu.edu.
Researchers from Columbia University working at the MagLab have observed a physical phenomenon in bilayer graphene that could usher in a new generation of quantum computers.
New kind of quantum Hall state observed in graphene superlattices.
Discovering previously unobserved quantum states nested inside the quantum Hall effect in a single-layer form of carbon known as graphene, researchers have found evidence of a new state of matter that challenges scientists' understanding of collective electron behavior.
This experiment probes the nature of the 12/5 Fractional Quantum Hall state by using a hydraulic-driven rotator to tilt the two-dimensional system in a magnetic field.
The work by Chen et. al. explores the quantum hall effect (QHE) that develops in BiSbTeSe2 at low temperatures and high magnetic fields. BiSbTeSe2 is a topological insulator, meaning it is a bulk insulating material that at low temperatures develops a quantum mechanical state that allows conduction of electrons at the surface similar to a metal. The observation of the QHE in BiSbTeSe2 is further confirmation of the theory governing these unique materials.
Using the 45T hybrid magnet, researchers uncover the quantum Hall effect in hydrogenated graphene.
Two independent research teams observed same behavior in double bilayer graphene.