'Topological insulators' promising for spintronics, quantum computers

November 13, 2014 by Emil Venere
Purdue University doctoral student Yang Xu, lead author of a new research paper on "topological insulators," an emerging class of materials that could make possible "spintronic" devices and practical quantum computers far more powerful than today's technologies, is shown here inspecting devices made from topological insulators under a microscope before electrical measurements. Credit: Purdue University photo / Ting-fung Chung

(Phys.org) —Researches have uncovered "smoking-gun" evidence to confirm the workings of an emerging class of materials that could make possible "spintronic" devices and practical quantum computers far more powerful than today's technologies.

The materials are called "topological insulators." Unlike ordinary materials that are either insulators or conductors, topological insulators are in some sense both at the same time - they are insulators inside but always conduct electricity via the surface. Specifically, the researchers have reported the clearest demonstration of such seemingly paradoxical conducting properties and observed the "half integer quantum Hall effect" on the surface of a topological insulator.

"This is unambiguous smoking-gun evidence to confirm theoretical predictions for the conduction of electrons in these materials," said Purdue University doctoral student Yang Xu, lead author of a paper appearing this week in the journal Nature Physics.

Yong P. Chen, a Purdue associate professor of physics and astronomy and electrical and computer engineering, led a team of researchers from Purdue, Princeton University and the University of Texas at Austin in studying the bismuth-based material.

"This experimental system provides an excellent platform to pursue a plethora of exotic physics and novel device applications predicted for topological insulators," Chen said.

For example, by further combining topological insulators with a superconductor, which conducts electricity with no resistance, researchers may be able to build a practical quantum computer. Such a technology would perform calculations using the laws of quantum mechanics, making for computers much faster than conventional computers at certain tasks such as database searches and code-breaking.

"One of the main problems with prototype quantum computers developed so far is that they are prone to errors," Chen said. "But if topologically protected, there is a mechanism to fundamentally suppress those errors, leading to a robust way to do quantum computing."

The topological insulators were synthesized at Purdue and fabricated into electrical devices at the Birck Nanotechnology Center in the university's Discovery Park.

The researchers for the first time demonstrated a three-dimensional material with an electrical resistance not dependent on the thickness of the material, a departure from conventional behavior. Whereas electrons usually have a mass, in the case of topological insulators the conducting electrons on the surface have no mass and are automatically "spin polarized," leading to the unique half-integer quantum Hall effect observed and also making the material promising for various potential applications.

Topological insulators could bring future computing platforms based on "spintronics." Conventional computers use the presence and absence of electric charges to represent ones and zeroes in a binary code needed to carry out computations. Spintronics, however, uses the "spin state" of electrons to represent ones and zeros.

"Compounds based on bismuth, antimony, telluride and selenide are the cleanest and most intrinsic topological insulators demonstrated so far, with no measurable amount of undesirable conduction inside the bulk that often spoils the topological conduction properties in earlier topological insulator materials," Chen said.

The researchers also found evidence consistent with the conduction of electrons being "topologically protected," meaning its surface is guaranteed to be a robust conductor. Studying thin-slab-shaped samples cut from this material down to ever decreasing thickness while observing the conductance, the researchers found that the conductance - which occurs always and only at the surface - barely changes.

"For the thinnest samples, such topological conduction properties were even observed at room temperature, paving the way for practical applications," Xu said.

The paper was authored by Xu; Purdue research scientist Ireneusz Miotkowski, who created the high-quality materials; Princeton postdoctoral research associate Chang Liu; Purdue postdoctoral research associate Jifa Tian; UT Austin graduate student Hyoungdo Nam; Princeton graduate student Nasser Alidoust; Purdue graduate student Jiuning Hu; Chih-Kang Shih, Jane and Roland Blumberg Professor at UT Austin; M. Zahid Hasan, a Princeton professor of physics; and Chen.

In addition to the material growth and electrical measurements performed by the Purdue researchers, the Princeton and UT Austin groups contributed to this study by performing advanced characterizations that further confirmed important properties of the material as a .

Explore further: Topological insulators could exist in six new types not seen before, theorists predict

More information: Observation of topological surface state quantum Hall effect in an intrinsic three-dimensional topological insulator, Nature Physics (2014) DOI: 10.1038/nphys3140

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grondilu
5 / 5 (1) Nov 13, 2014
> and practical quantum computers far more powerful than today's technologies.

I'm a bit uneased by those claims about quantum computers being more powerful than today's. If I understand correctly, quantum computers would be efficient only in a fairly narrow set of applications. Quantum computers will not make GTA 6 run faster for instance, which of course is what really matters in the end :-)
imido
Nov 13, 2014
This comment has been removed by a moderator.
Virex
3.5 / 5 (2) Nov 14, 2014
Imido: The D-wave computer isn't a propper quantum computer, but a quantum annealer and as such, their results do not have any bearing on real quantum computers.
Selena
Nov 14, 2014
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swordsman
not rated yet Nov 14, 2014
"...a plethora of exotic physics" ? Must have been designed by the Three Amigos.
dtxx
not rated yet Nov 14, 2014
> and practical quantum computers far more powerful than today's technologies.

I'm a bit uneased by those claims about quantum computers being more powerful than today's. If I understand correctly, quantum computers would be efficient only in a fairly narrow set of applications. Quantum computers will not make GTA 6 run faster for instance, which of course is what really matters in the end :-)


I can't honestly tell you what the potential of a desktop quantum computer would be. I would guess the first ones will be hybrid with standard cpu and ram integrated.

But as to their narrowness, at least for now, they are being designed that way on purpose. Even ASICs can have surprising uses outside their designed purpose. For example, gluing a bunch of computer graphics cards together is surprisingly effective and economical way to make a world class supercomputer for tasks like protein folding. Maybe ASQCs will surprise us too.

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