Nearly a decade ago, theorists predicted the upside-down world of topological insulators, which were supposed to possess the peculiar property of being insulators on the inside but conductors on the outside. While the theories were experimentally confirmed just a couple of years later, making practical devices out of the material has remained a largely unsolved challenge.
Now researchers at Purdue University claim they have found evidence that is the “smoking gun” proving that topological insulators are indeed a path towards realizing practical quantum computers as well as “spintronic” devices that are far more powerful than today’s number crunchers.
The “smoking gun” in this case comes in the form of something called a half-integer quantum Hall effect on the surface of a topological insulator. This is an effect that is seen in graphene in which there is a no resistance plateau at a zero magnetic field.
“This is unambiguous smoking-gun evidence to confirm theoretical predictions for the conduction of electrons in these materials,” said Purdue doctoral student Yang Xu, lead author of the paper detailing the discovery, in a press release.
The research, which appears in the journal Nature Physics, demonstrated for the first time that a three-dimensional material’s electrical resistance did not have to be dependent on the thickness of the material.
The researchers discovered further evidence that the conduction of electrons were topologically protected in these materials, which means their surfaces are guaranteed to be robust conductors. In the experiments, the researchers would slice off thin layers from the surface of the material and after each thinning of the material, the surface maintained its conductance without the slightest change.
“For the thinnest samples, such topological conduction properties were even observed at room temperature, paving the way for practical applications,” Xu said in the release.
This conduction on the surface of topological insulators is important for spintronic devices. The unique applicability of topological insulators to spintronic devices comes from the fact that the conducting electrons on the surface have no mass and are automatically “spin polarized,” leading to the unique half-integer quantum Hall effect that was observed in this research.
This past summer, researchers at Penn State and Cornell University provided one of the first promising indications that it might actually be possible to derive practical applications such as spintronic devices from these topological insulator materials.
In addition to spintronics, researchers believe that topological insulators, when combined with superconductors, could lead to a practical quantum computer.
“One of the main problems with prototype quantum computers developed so far is that they are prone to errors,” said Yong P. Chen, a Purdue associate professor, in the press release. “But if topologically protected, there is a mechanism to fundamentally suppress those errors, leading to a robust way to do quantum computing.”
Chen added: "This experimental system provides an excellent platform to pursue a plethora of exotic physics and novel device applications predicted for topological insulators.”