Professor of Physics David Hall ’91, working with a team of recent physics graduates, has published a paper about his recent discovery of a three-dimensional skyrmion in an experiment with unusual electromagnetic-like properties.
Though trained as an atomic physicist, Hall was drawn to topology, a branch of mathematics that focuses on the continuous deformation of shapes. “Topology is that thing that lets you distinguish shapes from one another, and it involves taking a shape and possibly deforming it in some way,” he said.
In order to conduct his studies on quasiparticles, Hall and his team first formed a superfluid by lowering atoms to billionths of a degree below zero, creating a “flow of atoms without any viscosity.”
He then studied how quasiparticles introduced to the superfluid behave. Hall’s earlier research discussed how monopoles — “simple point objects,” according to Hall — acted in superfluid. He then worked with knots, which is essentially an extended object — “a twisting that can’t untwist itself,” explained Hall.
Hall’s most recent work has focused on skyrmions. His recent publication indicates that “not only is the [skyrmion] knotted, but the electromagnetic field-equivalent is also knotted.”
Throughout his topological studies, Hall has collaborated with Aalto University in Finland. He discussed how, prior to their cooperation on publications, he studied vortex-like particles similar to those that Aalto researchers were working on.
“We did this neat vortex experiment… I was working with some theorists at UMass, and we were actually competitors there, at the beginning … and they published their paper first, much to my chagrin,” said Hall.
Mikko Möttönen, the principal investigator from the Aalto research team, reached out to offer advice on adjusting their experiment. Over time, the professors from both universities developed a partnership.
Two of Hall’s former thesis students, Andrei Horia Gheorghe ’15 and Wonjae Lee ’16, were also involved in the research on the three-dimensional skyrmion.
“I was really interested in this project, as we discovered that the spin texture of the skyrmion shows the electromagnetic knot structure, which is analogous to the ball lightning,” Lee said in an email interview. “Ball lightning is a natural phenomenon which hasn’t been explained yet, and we think that studying this skyrmion structure will help us with understanding the ball lightning structure too.”
Hall added that his future research will likely focus on the dynamics of these quasiparticles. “The first thing we wanted to do was learn how to make [skyrmion], and the second thing we want to do is then discover what they do,” said Hall. “It may give us a hint into what’s happening in the universe.”
