Ordinary materials are either insulators or conductors, but topological insulators are both — they insulate inside but conduct electricity on the surface. They might be used for spintronic devices and to make powerful quantum computers.

This microscope image shows a new device used to measure the “persistent spin polarization” for a rechargeable spin battery.
(Photo credit: Purdue University/Jifa Tian)

Electrons have two spin states: up or down, and a phenomenon known as superposition allows electrons to be both at the same time. This could be harnessed to perform calculations using the laws of quantum mechanics, creating computers that are much faster at certain tasks.

The conducting electrons on the surface have a key property known as “spin-momentum locking,” in which the direction of the motion of electrons determines the direction of its spin.

“Because of the spin-momentum locking, you can make the spin of electrons line up or ‘lock’ in one direction if you pass a current through the topological insulator material, and this is a very interesting effect,” says Yong P. Chen, professor of physics and astronomy and electrical and computer engineering. He is the director of the Purdue Quantum Center.

Applying an electric current induces an electron “spin polarization.” Ordinarily, the current must remain turned on, but Purdue researchers are the first to induce a spin polarization lasting two days even when the current is turned off.

The findings are detailed in a research paper, which appeared April 14 in the journal Science Advances. The experiment was led by postdoctoral research associate Jifa Tian.

The paper was authored by Tian; Seokmin Hong, former Purdue doctoral student and engineer at Intel Corp.; research scientist Ireneusz Miotkowski; Supriyo Datta, Purdue’s Thomas Duncan Distinguished Professor of Electrical and Computer Engineering; and Chen.