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.
High precision NMR studies of dilute impurities in solid 4He have demonstrated the existence of an unexpected lattice relaxation at low temperatures (T<0.2K). This new effect is attributed to the quantum plasticity reported in studies of the elastic constants in the same temperature regime.
High magnetic fields have been shown to induce strong electric polarizations in the doped organic quantum magnet, dichloro-tetrakis-thiourea, or DTN. The introduction of disorder in DTN leads to the formation of Bose glass states and the electric polarization is particularly enhanced at the transitions to the glass state.
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.
New research at the lab’s High B/T facility supports the proposal that the disordered ground state of terbium titanate is a quantum spin ice.
This week at the lab our new chief scientist is on the road, connecting the dots that are the National MagLab’s many instruments, techniques and experts.
Physicist Laura Greene, who was named the lab’s chief scientist last year, traveled from the lab’s Florida State University headquarters to the University of Florida in Gainesville, home to two of the lab’s seven user facilities: the High B/T Facility and the Advanced Magnetic Resonance Imaging and Spectroscopy facility (AMRIS).
Greene (pictured above left with Tom Mareci and Joanna Long of AMRIS) will learn about the special capabilities the facilities offer, including dynamic nuclear polarization (DNP), a promising technique under development at AMRIS and at the MagLab’s Tallahassee-based Nuclear Magnetic Resonance Facility. More familiar to biologists and chemists, DNP may also be a powerful tool for condensed matter physicists, said Greene. President-elect of the American Physical Society, Greene says a big part of her MagLab job will be identifying and building these types of fertile, cross-disciplinary relationships.
When scientists learn from colleagues at a different facility or lab about the research they are working on it, "People are astounded and excited by it," said Greene. "But then they go back and they’re busy. So it’s going to be my job to help keep the flywheel going … to keep it as single MagLab, make sure we learn from each other."
Greene hopes the connections she is fostering will result both in more scientific publications authored by MagLab staff from multiple facilities as well as publications spawned by collaborations with other national labs and industry. Through her work with the Center for Emergent Superconductivity, Greene has close ties to both Brookhaven and Argonne national laboratories.
Photo by Elizabeth Webb / Text by Kristen Coyne
This week at the lab, a Canadian scientist working in Gainesville, Florida, is trying to detect something never before seen in experiments that require temperatures so frigid not even a Mountie could endure them.
And because cold makes everything from parka-puffy children to atoms slow down, he is in the Sunshine State for the long haul. While experiments at the MagLab's six other facilities typically last a week, scientists using the instruments at the MagLab's High B/T Facility on the University of Florida campus usually hunker down for several months.
The "B" and "T" in "High B/T" stand for magnetic field and temperature, respectively. Scientists who use these unique systems are looking at samples at very high fields and at temperatures so low they hover just above absolute zero. It takes weeks to get the magnet that cold and for the samples inside it to adjust.
"At these extremely low temperatures, there's very little motion left, very few degrees of freedom," explained High B/T Facility Director Neil Sullivan. "So you can wait a long, long time to get to the state of thermal equilibrium."
Simon Bilodeau, a graduate student in the group of Guillaume Gervais at McGill University in Montreal, is a few weeks into a three-month stint in Gainesville using a 16.5 tesla superconducting magnet. The experiments require constantly adjusting the magnetic field for new data.
"You might get two measurements done in the course of a day at one temperature, one field," said Sullivan. "Then you move on to the next one — move the temperature, move the field, wait for equilibrium again, prove you've got equilibrium, measure the temperature, then go ahead and take the measurement. You might get two points on a graph in a day. So if the graph has, say, 100 points, there's 50 days."
While the details on this experiment are being kept under wraps for the time being, Bilodeau is looking for a new effect that has been predicted but so far not proven, said Sullivan. It's a very difficult but exciting "high-risk" experiment: It could end with a big publication or be more or less a bust.
"If we aren't occasionally taking risks and doing experiments that look for new effects," said Sullivan, "even where we might fail, then, maybe, we aren't doing the right thing."
Main image by Dave Barfield / Secondary image courtesy of Neil Sullivan / Text by Kristen Coyne.
This week at the lab, a dozen elementary school teachers toured the MagLab’s High B/T Facility as part of a science conference on the University of Florida (UF) campus.
The teachers are participating in the Annual Florida Regional Junior Science, Engineering, and Humanities Symposium. Hosted by UF's Center for Precollegiate Education and Training, the symposium provides opportunities for high school students and K-12 teachers to visit UF's research facilities and meet and interact with scientists and engineers.
The teachers were eager to see science in action at the High B/T Facility, where scientists conduct months-long experiments at extremely high magnetic fields (that's what the "B" stands for) and extremely low temperatures (that's the "T"), environments that make this facility unique in the world.
Facility Director Neil Sullivan led the group through the lab with the help of Postdoctoral Associate Alessandro Serafin and Senior Engineer Naoto Masuhara. Serafin showed the teachers the "ultra-quiet shielded room" for one of the experimental areas, where he is laying the groundwork for an upcoming experiment on magnetic torque in a topological insulator. This follows a year-long experiment by a Wayne State University scientist.
Sullivan then explained the facility's helium cooling system, which uses helium-3, a rare helium isotope, and magnetic refrigeration to cool the sample to temperatures near absolute zero. "We are looking for people who are both scientists and plumbers," Sullivan said, pointing to the network of pipes and valves that regulate helium in the facility.
The last stop on the tour was the basement, where participants could see the concrete tripods that support and protect the magnets by dampening vibrations that threaten to raise the low temperatures needed for these experiments. "These tripods are 35 feet below ground," Sullivan explained. He added that there are additional measures in place above ground to protect the workspace from radio waves that would also increase molecular vibrations and the temperature of the sample.
The teachers left engaged and excited by the tour, snapping photos of a chalkboard full of calculations and drawings to show their students.
Text and photo by Elizabeth Webb