Scientists create 2D electronic kagome lattice

Wednesday, 05 December, 2018

Scientists create 2D electronic kagome lattice

Australian and Chinese scientists have created an atomic-scale, two-dimensional electronic kagome lattice — named after a traditional Japanese woven bamboo pattern composed of interlaced triangles and hexagons — with potential applications in electronics and quantum computing.

As explained by Dr Yi Du, based at the University of Wollongong (UOW), scientists have long been interested in making a 2D kagome lattice because of the useful theoretical electronic properties such a structure would have.

“Theorists predicted a long time ago that if you put electrons into an electronic kagome lattice, destructive interferences would mean the electrons, instead of flowing through, would instead turn around in a vortex and would become locked in the lattice,” he said. “It is equivalent to someone losing their way in a maze and never getting out.

“The interesting point is that the electrons will be free only when the lattice is broken, when you create an edge. When an edge forms, electrons will move along with it without any electric resistance — it has very low resistance, so very low energy and electrons can move very fast, at the speed of light. This is of great importance for designing and developing low-energy-cost devices.

“Meanwhile, with a strong so-called spin-orbital coupling effect, novel quantum phenomena, such as frictional quantum Hall effect, are expected to happen at room temperature. This will pave a way for quantum devices in the future.”

But while the theoretical properties of an electronic kagome lattice made it of great interest to scientists, creating such a material has proved extremely challenging. Dr Du explained, “For it to work as predicted, you have to make sure the lattice is constant, and that lengths of the lattice are comparable to the wavelengths of the electron, which rules a lot of materials out.

“It has to be a type of material on which the electron can only move on the surface. And you have to find something that is conductive, and also has a very strong spin-orbital coupling effect.

“There are not many elements in the world that have these properties.”

One element that does is silicene — a silicon-based, one-atom thick, Dirac fermion material with a hexagonal honeycomb structure, which electrons can speed across at close to the speed of light. When silicene is twisted into a kagome lattice, however, the electrons should become ‘trapped’, circling around in the hexagons of the lattice.

Working with Beihang University, Nankai University and the Chinese Academy of Sciences, Dr Du and his UOW colleagues created their own 2D electronic kagome lattice by layering and twisting two nanosheets of silicene. At a rotation angle of 21.8° they formed a kagome lattice — and when the researchers put electrons into it, it behaved as predicted.

“We observed all the quantum phenomena predicted theoretically in our artificial kagome lattice in silicene,” Dr Du said.

Described in the journal Science Advances, the expected benefits of this breakthrough will be much more energy-efficient electronic devices and faster, more powerful computers.

Top image caption: Diagram of destructive quantum interference inducing an FB in the kagome lattice. Three different sites (A, B and C) are marked with three different colours (blue, white and red, respectively). Image has been cropped from the original and is shared courtesy of the study authors under CC BY-NC 4.0

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