Erik Henriksen, assistant professor of physics in Arts & Sciences at Washington University in St. Louis, has been awarded a prestigious Faculty Early Career Development (CAREER) Award by the National Science Foundation. His grant, expected to total $850,000 over the next five years, is for research that explores many-particle interactions in graphene and other single-atom-thick materials.
The behavior of electrons determines the fundamental properties of any material — such as its ability to conduct electricity, or its reflectivity. But these electron interactions are mostly impossible to directly perceive.
“The odd reason that no one has been able to investigate this is that spectroscopic techniques are blind to correlated motion of electrons in most materials,” Henriksen said. “In graphene, amusingly enough, spectroscopy does work and can directly observe the appearance of such many-particle effects.”
Henriksen painstakingly built a unique facility at Washington University that allows him to shine infrared light through graphene under the influence of a strong magnetic field, at extremely low temperatures — revealing the fundamental ways in which electrons jostle with each other as part of a larger system.
“We want to perform spectroscopy of the fractional quantum Hall effect, a remarkable many-particle correlated electron effect discovered in the 1980s,” he said. Henriksen’s graduate adviser Horst L. Stormer was awarded the 1998 Nobel Prize in physics for his role in that discovery. “This effect is characterized by strange features such as apparent fractional electron charges and electrons that bind to magnetic field lines.”
Henriksen also will use funds from his CAREER grant to place atomically small slivers of materials between two mirrors, trapping the light such that it bounces back and forth through the slivers thousands of times.
“Ultimately, this creates novel particles that are a quantum mixture of light and matter: a new form of stuff that doesn’t normally exist,” Henriksen said. “With graphene and our low-temp facility, we can do this in a new regime no one has looked at before.
“Hopefully, this means we’ll find new behaviors,” he said. “Or, at the very least, we can enhance the correlated effects.”
Henriksen plays a key role in the university’s Center for Quantum Sensors. To that end, he also is working to develop novel graphene-based infrared sensors and light emitters operating in the so-called ‘terahertz gap,’ a part of the infrared spectrum that is historically bereft of convenient sources and detectors.
In a forthcoming paper at Physical Review X, a scientific journal of the American Physical Society, Henriksen directly observed many-particle effects and how they show up as unusual gaps in the electronic structure of graphene.
“Many materials can be understood as if the electrons inside were unaware of or unaffected by each other,” Henriksen said. “It’s weird but true. But when you find a material where this is not the case, things get very interesting!”