What started as chats over tea between Physics PhD student Connor Wilson (BSc ’21, MSc ’23) and Assistant Professor of Physics Ganesh Ramachandran became a mission to solve something of a cold case in their field.

The mystery is why solid lithium — a mineral used to produce rechargeable batteries and some mental health medications — behaves differently than other solid materials at cold temperatures.

“It has been known since 1947 that lithium has strange properties,” says Ramachandran, Wilson’s PhD supervisor. “Over these decades, people have done experiments with contradictory results and lots of hypotheses put forward, but there has been no explanation so far as to why lithium’s structure is disordered in extreme cold.”

Normally, the arrangement of atoms is most “ordered” — forming a regular pattern — when a solid is cold. As the solid heats up, defects appear and atoms can become less ordered — by slipping out of alignment, for example — until the material eventually melts.

Solid lithium is highly ordered at room temperature. When cooled below -200 C, however, it suddenly loses its regular arrangement.

“It appears to form a random structure with many defects,” says Ramachandran. “Unlike other solids, lithium loses order when cooled, an abnormality that intrigues us.”

The quest to solve the puzzle began with Eric He, an undergraduate student attending another university who Ramachandran hired during the summers of 2023 and 2024 with support from the National Science and Engineering Research Council of Canada, which is funded by the federal government.

While working with Ramachandran, He produced a series of numerical calculations related to the arrangement of atoms within lithium.

Ramachandran and Wilson verified those calculations and Wilson continued to advance He’s work. After much discussion, the duo landed on a possible explanation for what happens when lithium is cold.

Lithium is closely packed with layers of atoms. At warmer temperatures, the layers self-stack on top of each other efficiently so that the atoms take up as little space as possible.

When lithium cools down, however, the stacks start to shift and “fight” with one another, says Ramachandran, with some layers stacking one way and some layers stacking another way.

“Past researchers observed that the structure of lithium seems random at low temperatures and doesn’t look like any other solid,” he says. “They thought it looked distorted but it must have some consistent structure. Our theory is that it’s not a complicated structure; rather lithium is frustrated.”

In physics, the term “frustrated” refers to a situation where competing interactions — such as shifting layers of atoms — prevent a system from reaching a stable state where all interactions are fulfilled.

Ramachandran says that, in the short term, insights gained from the team’s research will deepen other physicists’ understanding of lithium so that the theory can be advanced.

The team’s findings are found in their study, “Metallic Bonding in Close-Packed Structures: Structural Frustration from a Hidden Gauge Symmetry,” published last December in the journal Physical Review Letters.

Wilson says he appreciates the approach his supervisor took during the research process.

Having a personal connection with his supervisor and the time and space to explore concepts results in creative, exciting ideas, says Wilson, adding that similar opportunities can be rare at larger institutions.

“I can come to Dr. Ramachandran with any physics problem, and we’ll sit here for hours and drink tea and solve problems together,” says Wilson.