Assistant Professor of Theoretical Physics
Gil Refael | California Institute of Technology
Secrets of Superconductivity
Gil Refael is an expert on the puzzling problem of superconductivity, electrons flowing without resistance. To grasp it, think of bumper cars.
Normally, when electrons try to carry electrical current through metals, they collide with each other as well as with other obstacles -- like bumper cars at an arcade. And that leads to a mess.
In a superconductor, electrons zip past at top speed, ignoring obstacles, like cars on a superhighway. Parts of superconductivity have baffled theorists for decades and applications for the current technology are scarce - cell phone towers, power lines, a few kinds of motors. Refael may be able to help.
The specialized work of understanding disordered superconductors -- those that make it particularly tough for their electrons to flow -- has been central to Refael's work since the beginning of his career.
His research boils down to the question: "What's the secret of the worst superconductor ever?"
By the "worst superconductor," Refael means a metal in which otherwise orderly electrons behave in ways that are anything but orderly, as they might in a vacuum.
"If the superconductor is cluttered with junk, impurity atoms, little structures, distractions on a road to nowhere, how does that change the electron behavior?" he wonders.
In superconducting metals, like lead or tin, you have something like a crystal structure that allows organized motion by electrons. They move predictably from atom to atom to atom.
But the metal compounds he studies are not like that. "Some metals are like glass - just molecules set in a random fashion. In them, electrons are bumping into themselves randomly."
To use the colliding bumper cars analogy, the electrons couldn't cross the track without having a collision, or many.
Particular metals - called amorphous metals, like molybdenum germanium or indium oxide -- can be used to make small superconducting devices, but because of the disorder, they are less than ideal from an engineering perspective, Refael says. "To know how to make superconductors, we need to understand more about the nature of these materials."
This sort of theory may help explain the behavior of electrons on the tiny films and wires that will be used in future generations of superconducting nanodevices.
Refael studied first in Tel Aviv, then received a Ph.D. at Harvard in theoretical condensed matter physics, and did post-doctoral work at UC Santa Barbara before joining Caltech in 2005. In 1994, he won a bronze medal for Israel at the International Physics Olympiad in China.
One problem bothering theorists is that a magnetic field can suppress superconductivity in films, driving the film into the opposite state - an insulator, where electrons cannot move at all. "We don't understand why superconducting films become insulators," Refael says. Figuring out the answers, he says, is still far down the theoretical road. But the knowledge will be valuable indeed.
"You've got to anticipate," he says. "If you know what happens to a superconductor with a current, with a magnetic field, then you will know the technical limits, and how to overcome them."
The physics describing many interacting electrons is still out there to discover, Refael says, and it is a challenge indeed. But he says the prime notion that gives hope that we can get there, is the principle of universality. "Just zoom out, and you will see the patterns that apply no matter what the small details are," he said.
And that's his goal: zooming out, seeing those patterns and grasping the behavior of the electrons in disordered superconductors, in the thinnest of films and wires that one day may revolutionize electronics.
Education Component
Refael will seek to make the learning of physics more interconnected across courses. He will devise a competition, throughout the year, in which students will compete to solve complex problems requiring them to use ideas from various classes. The problems will have no easy answers, like, say the motion of debris in space, or satellites, or even earthquakes or lightning. They may take up to five hours to solve, and prizes will be based on ability to integrate course materials.
