Nov 06 2018

Electron Quantum Metamaterials

Material science is, in my opinion, one of the most underappreciated of the sciences. Perhaps because it is so wonky, it doesn’t seem to get much public attention, and yet the development of new materials arguably has the potential to change our civilization more than any other single advance. Our level of technology is largely defined by the materials we have mastered, and discovering a new material is literally a technological game changer.

It’s always hard to predict the next big advance, but there are some intriguing candidates. Interest seems to be clustering around anything on the nano scale – such as carbon nanofibers. Two-dimensional materials that are only one or a few atoms thick (which includes carbon nanofibers) is an area of intense research as well. There is also a relatively new class of materials called metamaterials, which do interesting things with light and other forms of electromagnetic radiation. Metamaterials essentially have emergent properties, and could have potentially exotic applications such as rendering objects invisible in certain frequencies.

A new paper attempts to codify and name one particular type of metamaterial that the authors (Justin C. W. Song & Nathaniel M. Gabor)  are proposing be called “electron quantum metamaterials.”

These types of materials are comprised of two or more layers of two-dimensional nanomaterial that are rotated with respect to each other so that special patterns emerge. This is likened to a moire pattern, where two sets of thin parallel lines are offset from each other by a certain amount and that creates an interference pattern. The interference patterns emerges from the specific relationship between the lines.

Similarly, if you take two layers of, say, carbon nanosheets and rotate or shift them with respect to each other, at certain angles of rotation you get emergent properties that affect how electrons move through the material. In this way you can “tune” the material to make it a superconductor, or insulator, or anything in between. They write:

An alternative, and rapidly progressing, nanotechnology is that of van der Waals (vdW) heterostructures1, wherein stacks of atomically thin materials are assembled to form a complex quantum system. This has been driven from multiple angles, including the proliferation of available atomic-layered materials1,2,3 over a wide range of phases such as semiconductors, semimetals, superconductors, ferromagnets and topological insulators; means of assembling high-quality vdW stacks (for example through mechanical pick-up/transfer assembly4,5); and theoretical proposals of how these materials, when combined, can conspire to produce new physical phenomena.

This approach has been applied to light in metamaterials, but they authors argue there is even more potential with electrons because electrons interact with each other much more than photons. Therefore the potential for emergent interference type effects is much greater. The result may be designer materials with not only optimal properties in terms of electronics and other applications, but perhaps new functions entirely.

The paper itself gets very technical, and you essentially have to be a physicist to follow much of it, which again is likely why I think public attention is less than what it deserves. Also, material science is a couple of steps away from specific applications. It takes a little more imagination to realize how important such material can be to our lives. These kinds of developments are worth paying attention to, however.

It seems were are in a phase with this technology that the basic science is advancing quickly, and demonstrating amazing potential. Translating this to specific products, however, is proving difficult. The limiting step is producing nanomaterials in bulk with sufficient quality control and at an acceptable cost. We may be able to develop amazing materials, but they will remain prohibitive to produce. They may still find appilcations in NASA probes and other extremely high-end applications, but we won’t be seeing them in our smart phones anytime soon.

This is often the variable that is hardest to predict, and is also the one that I find is the least reported on. Unless you are in the industry, it’s hard to know where we are with this. The media tends to report only the exciting basic science with speculation about amazing applications, but knowing how plausible or close those applications are is rarely reported in any detail. When I do try to understand and report on it, it is often the case that someone on the inside will e-mail me to let me know the actual situation is far different than what is being reported. That’s OK – at least then I know who to talk to in order to get a better picture of what’s going on.

In any case – it seems that electron quantum metamaterials are a potentially new class of materials with exciting properties. The authors lay out the relevant physics. I still have no idea whether this is the kind of thing we will be seeing in applications in 10 years or 50 years. Perhaps someone reading this has a better sense.


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