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Physicists take one step closer to the construction of a graphene-based topological insulator



  Physicist takes a step closer to the construction of a graphene-based topological isolator
Andrea Young. Credit: SONIA FERNANDEZ

In 2005, condensate physicists Charles Kane and Eugene considered the fate of the graph at low temperatures. Their work led to the discovery of a new matter called a "topological isolator," which would launch a new era of material science.

"A topological insulator is a material that is an insulator in its interior but is very conductive on its surface," says UC Santa Barbara assistant physics professor Andrea Young. In two dimensions, an ideal topological isolator would have "ballistic" conductance at its edges, Young explained, meaning that electrons traveling through the region would encounter zero resistance.

Ironically, Kane and Mele would work lead to the discovery of topologically insulating behavior in a wide variety of materials, their original prediction of a topological isolator in the graph having remained unrealized. In the heart of the trouble, the spin-path coupling is a weak effect in which the rotation of the electron interacts with its orbital movement at the core. Critical to all topological insulators, the spin-path coupling is extremely weak in the graph, so that any topologically insulating behavior is drowned out by other effects derived from the surface on which the graph is supported.

"The weak orbit in the graph is a great shame," says postdoctoral researcher Joshua Island, because in practice it has not worked so well for topological insulators in two dimensions. " Particularly easy to work with, "said Iceland. The conductance at the edges tends to decrease rapidly with the distance traveled by the electrons, indicating that it is far from ballistic. Realizing a topological insulator in the graph, an otherwise very perfect two-dimensional material, would be able to form the basis for ballistic electrical circuits with low dispersion or form the substrate material for topologically protected quantum bits. isolator (TI). "The aim of the project was to increase or improve spin-b the ana link in the graph, "said lead author Iceland and added that attempts have been made over the years with limited success. "One way to do this is to put a material that has a very large swivel attachment near the graph. It was hoped that your graphene electrons would take on this property of the underlying material," he explained.

The choice of material? After studying several possibilities, the researchers settled on a dicalcogenide of transition metal (TMD), consisting of transition metal tungsten and chalcogen selenium. Similar to the graph, tungsten diselenide in two-dimensional monolayers, bound by van der Waals forces, which are relatively weak and spaced-apart interactions between atoms or molecules. However, unlike the graph, the heavier atoms of TMD lead to stronger spin-path coupling. The resulting unit function is the ballistic electron conductance of the graph with the strong spin-bed coupling from the adjacent TMD layer.

"We saw a very clear improvement on this spin-off link," says Iceland.

"By adding spin-path coupling of just the right type, Joshua could find that it actually leads to a new phase that is almost topologically insulating," says Young. In the original idea, he explained that the topological isolator consisted of one monolayer of the graph with a strong spin-path link.

"We had to use a trick only available in the graph's multilayers to create the right kind of spin-twist," Young explained about their experiments using a graphene-double layer. "And then you get something that approximates two topological insulators stacked on top of each other." Functionally, however, the island's unit and other known 2-D topological insulators perform. The generally important edge states spread for at least several microns, much longer than in other known TI materials.

Further, according to Young, this Work is a step closer to the construction of a real topological isolator with the graph. "Theoretical work has since shown that The graphical trilayer, made in the same way, would lead to a true topological isolator. "Most importantly, the units realized by Iceland and Young can easily be set between a topological isolation phase and a regular isolator, which does not have leading edge states.

"You can touch these perfect leaders around you," he said, "and there is nothing that has been able to do with other materials."


Explore the new spintronics device functionalities in graphenostructures


More information:
Spin-orbit-driven band inversion in the double layer graph by van der Waals proximity effect, Nature (201
9). DOI: 10,1038 / s41586-019-1304-2, https://www.nature.com/articles/s41586-019-1304-2

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Physicist takes a step closer to the construction of a graphene-based topological isolator (2019, June 12)
June 12, 2019
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