In a lab at Cornell University, physicist Paul Malinowski and his colleagues did something scientists had struggled with for years: they found a way to carefully control a stubborn material called iron selenide. And what they discovered turned a long-held idea about superconductors on its head.
Superconductors are materials that carry electricity with zero resistance — no wasted energy at all. But most only work at extremely cold temperatures. "High-temperature" superconductors work at slightly warmer (though still very cold) conditions, and scientists badly want to understand them because a room-temperature superconductor could transform everything from power grids to medical imaging.
For years, researchers assumed that the key to tuning a material like iron selenide was simply adding more electrons. More electrons, the thinking went, meant stronger superconductivity — up to a point. That rising-and-falling arc of strength is called the "superconducting dome," and it appears in many superconductor families.
But iron selenide refused to behave. Its chemistry resisted the usual ways of adding electrons, so Malinowski and his team had to invent a new approach. Instead of growing a brand-new material each time they wanted a different electron count, they grew one thin film using a method called molecular beam epitaxy, then sprayed electrons onto its surface using a gas of cesium atoms. Because the Shen lab is expert at making thin films, the team could measure the material's behavior immediately, without ever removing or regrowing the sample.
The results, published in the Proceedings of the National Academy of Sciences on August 20, surprised everyone. The dome in iron selenide was not driven by how many electrons were added. It was driven by disorder — tiny imperfections in the crystal lattice, like an atom sitting slightly out of place, that slow electrons down as they travel.
"It's not driven by how many electrons you're adding in, but rather, it's driven by the obstacles the electrons are hitting," said Malinowski, a former Klarman Postdoctoral Fellow. "How perfect or imperfect is the crystal lattice?"
This makes iron selenide stand apart from other families of high-temperature superconductors. In materials called cuprates, scientists believe electron number is the main driver. Here, the very act of adding electrons also adds disorder, and that disorder is what really shapes the dome.
The finding matters because it gives theorists a new clue about how high-temperature superconductivity actually works at the microscopic level. As lab director Kyle Shen put it, the team's precise control of the material was the key. The more scientists understand what controls these remarkable materials, the closer they get to unlocking their potential — and the closer we get to a future where electricity flows with nothing wasted.