Arrays of "Topological Insulators": a Step Towards Exotic Electronics

LilaG writes with a paragraph from Chemical & Engineering news: "Chemists in China have precisely grown arrays of ultrathin flakes of bismuth selenide and bismuth telluride on a surface. The bismuth compounds belong to a recently discovered – and weird — class of materials called topological insulators, which conduct electrons only along their surfaces, not through their insides. Researchers think topological insulators promise a new realm of fast, energy-efficient electronic and spintronic devices. Making well-defined nanoparticle arrays such as the new study's flakes is a key step towards such devices."

Comments

Lets hope

[Anonymous Coward]

They outsource manufacturing it to USA

Well, now

[Khyber]

Modifiable bandgaps for multi-wavelength LEDs, anyone? Multi-spectrum lasers?

Re:Well, now

[Anonymous Coward]

so what ? modulated shield frequencies is what matters.

Exotic Electronics

[Anomalyst]

Oboy, body contour hugging catsuits and padded manacles made of bismuth.
Count me in!

Good paper, but not a major breakthrough

[gotfork]

Being able to grow well-ordered arrays of bismuth selenide and bismuth telluride nanoplates is a great improvement over the original VLS/Van der Waals growth method developed by Cui's group, in which you could grow similar nanoplates but they were randomly distributed across the surface (it's a pain to work with them since you have to track whichever one you want to use down by hand). However, it's not a huge breakthrough in the field and doesn't put us much closer to any of the proposed devices which would actually use topological insulators. Although they don't show any transport data in the paper the quality of the nanoplates may not be that good based on the ARPES data shown -- the fermi level falls well into the conduction band, and not in the gap as would be required by most interesting applications. Also, a more commonly used technique called molecular beam epitaxy (MBE) can also be used to grow continuous films of these materials across whole wafers, and several groups have demonstrated very high quality films this way.
TL;DR: A nice scientific paper, on an exciting topic, but no major breakthrough. Several interesting uses for TIs have been proposed but they are all very far out, everything going on right now is still basic research. (Full disclosure: I'm not affiliated with either group, but I am sitting in the lab measuring some TI-based devices right now).

insulates .. until it cracks

[citizenr]

insulates .. until it cracks and all of a sudden there IS a surface between 2 previously insulated wires.

Re:insulates .. until it cracks

[Anonymous Coward]

Simple, put on a label that says do not bend.

Douch E. Bag MBA

Re:insulates .. until it cracks

[nedlohs]

Lots of current circuit boards won't work when snapped in half either.

Cracking one can touch two wires/tracks/pins that weren't touching before too.

Re:insulates .. until it cracks

[Anonymous Coward]

If you RTFA they describe it as somewhat self-healing. I.e. if the conductive surface cracked, there would just be new surface underneath, which would become conductive by nature of its being on the surface. This is why it's different from an insulator coated with a thin conductive layer (e.g. metal).

another bismuth compound

[treeves]

coats and soothes. I do not like the taste of Pepto-Bismol though.

A rather mysterious subject, though:

[Hartree]

I've been to a couple of talks on TIs and read very briefly on them. It's at the bare edge of my admittedly atrophied knowledge (20 years of doing things other than physics makes for a lot of forgetting).

Whenever an article on TIs comes up on slashdot, it gets few replies. I suspect that even those with some idea of what all the excitement is about find it hard to explain on a level that even some fairly cluefull slashdotters can understand. I've got some ideas of what it's about, (New electronic states to explore that are different in some ways than normal ones found in more common materials.) but don't understand it well enough to explain it well.

The applications are as you say, a ways off. But there seems to be a whole academic industry in characterizing them at the moment.

Even if they don't work out to give us the "magical topologically protected states that can be used for quantum computing" (tm) it's still some very interesting physics.

Re:A rather mysterious subject, though:

[Anonymous Coward]

I suspect that even those with some idea of what all the excitement is about find it hard to explain on a level that even some fairly cluefull slashdotters can understand. I've got some ideas of what it's about.

I actually work on TI's, and I would definitely agree with this. The most exciting and interesting aspects of the theory are profound but subtle, and difficult to appreciate unless you're a physicist. It is substantially more difficult to explain to other people why I am excited about this than my other work.

Briefly and simply: Topological insulators are materials that are electrically insulating in the bulk, but have metallic, conductive surfaces. This isn't just any kind of conductive state, though; it will feature an odd number of Dirac cones, like those that exist in graphene and give it its unique electronic properties. Furthermore, this cone is characterized by a spin texture which forbids direct back scattering. Now the cool thing is, this state is robust under perturbations and disorder - you can't get rid of it unless you turn either turn on a magnetic field(even then the results are interesting), or essentially destroy the material. This is because the state is *topologically* protected; in a (very) rough sense the electronic states in the bulk of the material get twisted around one another, and when you exit the material at an interface with a normal insulator, like air or vacuum, the states have to untwist themselves. This untwisting manifests as the Dirac cone(s) at the surface.

However, what I think is a bit easier is to convey is the broader impact:
1) Until very recently, all interesting phenomenon and phases of matter were understood as breaking of symmetry. Super conductivity, ferroelectricity, ferromagnetism, etc. This is the first serious case of a phase of matter that is marked by a difference in topology - the symmetry between a topological phase and trivial phase can be exactly the same, and the transition can't be described by an order parameter. This potentially signifies that there are a lot more interesting things that matter can do than we previously understood.
2) It marks a growing mathematical sophistication of the field. Ed Witten actually has started attending talks on this and related topics.
3) This was a case where theory made a startling prediction(a new phase of matter!) that was later confirmed by experiment. The state was unknown and it didn't even occur to anyone that it might exist until 2005 when it was mathematically described and characterized. A few years later it was found in a relatively common material, exactly as described by the theory.

Not through the insides?

[Anonymous Coward]

"... which conduct electrons only along their surfaces, not through their insides." I'm a bit of an ignoramus, but I thought ALL electricity flowed along the surface of conductors. Isn't that why cars are safe from lightning strikes?

Re:Not through the insides?

[MiG82au]

No. Only high frequency currents concentrate towards the surface. And I believe this has nothing to do with cars and lightning; that's just a matter of being enclosed in a conductive cage.