A topological insulator’s surface is not an ordinary metal. The direction and spin of the surface electrons are locked together and change in concert. Perhaps the most surprising prediction is that the surface electrons cannot be scattered by defects or other perturbations and thus meet little or no resistance as they travel. The surface states remain “topologically protected” – they can’t scatter without breaking the rules of quantum mechanics.
“One way that electrons lose mobility is by scattering on phonons,” says Alexei Fedorov, staff scientist at Berkeley Lab’s Advanced Light Source. Phonons are the quantized vibrational energy of crystalline materials, treated mathematically as particles. “Our recent work on a particularly promising topological insulator shows that its surface electrons hardly couple with phonons at all. So there’s no impediment to developing this TI for spintronics and other applications.”
The TI in question is bismuth selenide, on whose surface electrons can flow at room temperature, making it an attractive candidate for practical applications like spintronics devices, plus farther-out ones like quantum computers. Much of the research on electron-phonon coupling in bismuth selenide was conducted at beamline 12.0.1 by a team including Fedorov, led by Tonica Valla of Brookhaven National Laboratory.