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Physics Discovery Unlocks Ingredients of 2-D Sandwich

Everything that exists in the digital world—photos, tweets, online courses, this article—is stored as 1’s and 0’s. At the software level, this information is written as computer code. At the hardware level, that code is brought to life by billions of transistors turning on (1) and off (0).

Transistors are in everything from computers and smartphones to MP3 players and digital cameras. But the power and efficiency of transistors is limited by the materials available to construct them.

Now, researchers from Northeastern University have made a discovery that opens up a whole new field exploring materials for transistors, photodetectors, flexible electronics, and other applications.

The work—published recently in the journal Science Advancesinvolves 2-D crystals, which are super-thin materials only a few atoms tall. Combining two 2-D crystals forms a heterostructure. Until now, physicists thought 2-D crystals had to be very similar, with all the atoms to lining up perfectly, in order to form a new heterostructure.

“But nature always throws a curveball at you,” says Arun Bansil, University Distinguished Professor of Physics and one of the paper’s authors.

Associate professor Swastik Kar co-authored the paper with Bansil and other colleagues at Northeastern. They observed for the first time that two completely dissimilar 2-D crystals can be arranged one on top of the other, atom by atom, in such a way that they fit together nearly perfectly and produce completely new properties.

“It would be like making a club sandwich,” Kar said. “You can have something that tastes like bread and something that tastes like meat.”

But the key, Bansil explains, is not just to assemble a sandwich where you can taste each layer separately. “You want to have some cooking going on so you can get some new flavors.”

In the world of condensed matter physics, discovering that two very different 2-D crystals can form a heterostructure is like combining water and flour for the first time and creating dough. It gives way to virtually limitless possibilities for new 2-D materials.

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