News, On Campus

BC Researchers Discover New Phase of Matter

Boston College physics professor Kenneth Burch collaborated with a team of researchers from other universities to publish a paper on June 8 detailing the discovery of a new phase of matter in his BC lab.

“In science in general, we’re really interested in understanding, fundamentally, how do new phases emerge?” Burch said. “When we say phases, what we mean are things like, for example, when you cool water down … it goes from a gas, to a liquid, to a solid, and its properties are very different … but it’s just water.”

According to Burch, his team made the initial discovery by analyzing an elementary particle called the Higgs boson. Burch explained how the theory of matter relies on symmetry—a property that describes an object’s uniformity around an axis.

“If I have a square, I can only rotate it 90 degrees and it looks the same, right?” Burch said. “So, those two objects, it turns out, will behave very differently, and what’s happening when you get new phases of matter is you’re getting these changes in symmetry.”

Burch said that depending on a material’s state of matter, it changes symmetry, which results in “modes” or “excitations,” which are the different patterns of the material.

“They act like particles, [but] they’re not real particles,” Burch said. “And the properties are inherited from the material in which they arise, and they really tell you about the fact that you found a new phase of matter.”

Determining a material’s state of matter is not always obvious, Burch said, but the ability to measure these modes reveals the physics behind these phases. When analyzing a mode that had previously been discovered, Burch said the team found a new behavior. 

“What we determined was that this mode [is] also magnetic and that [it] had never been seen before,” Burch said. “As a result, we knew that that meant that this new phase of matter we saw had never been seen before, right? So it meant that it was actually breaking more than one symmetry at a time.”

As a result of this discovery in 2019, Burch said he and his team wondered why and how a new phase of matter could be possible, as well as if it could be applied to any other areas of science, specifically physics. 

“This Higgs mode … idea was originally developed in materials” Burch said. “It was then readapted to understand certain important fundamental questions in particle physics.

Particle physicists suggested that there may be another type of Higgs mode that had not been seen prior to this discovery, according to Burch.

“And so one question is, for example, does the properties of our mode suggest anything about how theories could be developed in other areas of physics?” Burch said.

Yiping Wang—a BC graduate student—worked alongside Birch in 2019 and was the first author of the paper. When measuring a material, Wang discovered that it responded very differently to scattering light depending on the orientation, an observation that had never been made before.

“So you see the particle one way, and you don’t see it the other,” Burch said. “And when she first showed me that, I thought, you have to be wrong, this can’t be true.”

After reproducing the results numerous times, the team concluded that its finding was concrete, and submitted a paper to nature, a science journal.

“Eventually, we realized that what we had seen was that this mode had this very special property,” says Burch. “So, back in September, we submitted a paper to nature, and it was reviewed, and reviewed again, and reviewed a third time, and then eventually it was published.”

June 28, 2022