A material that you may never have heard of could be paving the way for a new electronic revolution.
Using the high magnetic fields available at the NHMFL, users from MIT were able to observe a quantum spin hall (QSH) state in graphene. The QSH state results in two oppositely oriented spin currents flowing clockwise and counter clockwise around the edge of the graphene flake without dissipation effects. This discovery further advances the exciting work being done to bring about spin based electronics.
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.
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Utilizing the sensitivity of the NHMFL optics facility, a team of scientists from Georgia Tech, Sandia National Laboratories, Institut Néel, Université Paris-Sud and the NHMFL were able to observe collective oscillations of Dirac Fermions in graphene nanoribbons. The observed effect is tunable by varying the width of the graphene nanoribbons and the applied magnetic field. This observation raises the possibility of graphene based tunable THz devices.
Thanks to conditions created by the MagLab’s 45 tesla hybrid magnet, scientists have made a technological breakthrough on graphene: When they placed it on top of hexagonal boron nitride, graphene became a semiconductor.
This week at the lab, a MagLab physicist is developing a measurement technique that will help scientists identify and understand new states of matter in a new class of metals analogous to graphene.
The MagLab offers dozens of measurement techniques to scientists — everything from AC magnetic susceptibility to ultrafast magneto-optics. Brad Ramshaw of the MagLab's Pulsed Field Facility at Los Alamos National Laboratory (LANL) in New Mexico, is modernizing a technique called pulsed echo ultrasound.
If you yell across a valley to a canyon on the other side, you can figure out how far it is by measuring the time between your holler and the echo it generates. "That's what pulsed echo ultrasound is, except we're not doing it in the canyon," explained Ramshaw, whose project is funded by a two-year, $430,000 grant from LANL. "We're taking a little piece of material and we're yelling at it."
The twist is that instead of measuring distance (they already know the length of the material), they are measuring the speed at which the sound travels, which differs depending on the material, magnetic field and temperature. This data can shed light on the physics happening inside the material.
Of course, it's a little more complex than shouting across a canyon, Ramshaw explained. "We have an ultrasonic transducer — like the ones used for ultrasound imaging in a hospital, but much smaller — that sends a pulse of sound at the material. Then the sound travels across it, bounces off the end and comes back to the transducer."
It's no coincidence that Ramshaw is developing the technique at the Pulsed Field Facility, which houses instruments that create brief pulses of magnetic fields (measured in milliseconds) as strong as 100 tesla, the strongest such magnets in the world.
Fields that high, used in concert with this technique, are expected to reveal new physics about Weyl metals, which can be thought of as three-dimensional analogs of graphene. A one-atom thick compound with exciting properties — incredible strength, flexibility and electrical and heat conductivity — graphene holds great promise for communications, transportation and other industries. The hope is that Weyl metals will hold similar promise for electronics applications, but will be easier to manipulate and manufacture.
Scientists have been aggressively studying graphene since they learned how to make it in 2004. The technique Ramshaw is developing will open a new playground for physicists to explore its 3-D analog, including the unusual way its electrons behave, as if they had no mass.
The Pulsed Field Facility's world-record fields are, " … enough to do crazy electronic things to these materials," said Ramshaw. "This is a capability that users want and we now have the resources to develop it."
Text by Kristen Coyne
FSU researchers use MagLab's unique 9.4 tesla ICR machine to make discovery.