Joseph Heremans is used to making discoveries that “look a little like magic,” detecting unexpected properties in materials and figuring out how to generate electricity with heat in ways that were once considered only theoretically possible.
With a new federal fellowship that funds tenured faculty members’ “blue sky” research pursuits, and physics. “It’s fantastic to have an established career in research, and then suddenly be given the opportunity to start a completely new direction. It is rejuvenating.
“Bindu Nair, director of the Basic Research Office for the U.S. Department of Defense, explicitly told me to take big risks in the research funded by this program.”
The DOD Basic Research Office that sponsors the fellowship received 170 white papers for this year’s competition. Expert panels invited 27 proposals as finalists, from which the 11 fellows were recommended.
“The idea has to be extremely ambitious, and yet the proposal has to provide enough preliminary data to prove that it’s possible,” Heremans said. “It doesn’t have to build on what you’ve done before – it’s based on the fact you’ve delivered in the past, but you’re now not bound by your past. You can come up with new ideas and try them.”
In early 2023, Heremans and a graduate student in his lab, Brandi Wooten, led the work behind a paper in which they predicted and confirmed theoretical properties of solid materials known as ferroelectrics – which hinted at the possibilities Heremans will pursue during the fellowship.
Spintronics makes use of the spin of electrons in materials known as ferromagnets. In these materials, the atoms behave like tiny magnets that all align with each other to form a big magnet with an overall magnetic “moment” that generates a magnetic field around it. Magnons, or spin waves, are how these tiny magnets move in relation to each other, much like a crowd doing “the wave” at a football game.
The Heremans team worked for over a decade on the propagation of spin waves under the influence of temperature differences. Heremans is now turning to another class of materials known as ferroelectrics – materials that contain positively and negatively charged atoms (ions).
At the atomic level, strong local electric fields develop between these ions. Similar to how the tiny magnets align in ferromagnets, these local electric fields align with each other to form a ferroelectric material, with a net polarization moment.
The team hypothesized that the quasi-particles moving in wave-like patterns in ferroelectrics are the vibrations of the atoms themselves, called phonons. Preliminary data show that these phonons carry enough heat to change the heat conduction of the materials when an electrical field is applied externally, leading the team to propose that, since spin waves carry a spin current, the new quasi-particle in ferroelectric materials should carry a polarization current – an entirely new concept.
In this new work, Heremans will explore the theory that the flow of electric polarization – no magnetic field required – can be demonstrated experimentally and can be used for engineering functions similar to spin currents: controlling the flow of heat, generating electricity from heat, and transporting information about a thousand times faster than magnetic spins can.
Multiple classes of applications could follow.
“In principle, you can make polarization currents work as a heat engine. Second, you can modulate the heat conduction through a solid with an electric field, allowing you to make the thermal equivalent of a transistor,” Heremans said. “Third, and the most ambitious, would be devices that have logical memory, not based on magnetic spin waves but on polarization currents. They would consume less power, heat up less and wouldn’t require big power plants to run data centers.”
One advantage for the military would be the ability to minimize electromagnetic interference – specifically, enemy attempts to jam communication signals, he added.
Heremans has received U.S. Defense funding since 2010, but this opportunity feels special and, he said, places him among the “who’s who in experts doing work relevant to the DOD.”
“It’s really a chance to let the imagination run free.”
