Graphene becomes superconductive | Hacker News Reader

Graphene becomes superconductive

tohoku.ac.jp

183 pointsjonbaer38 comments

So far, most of the comments are lamenting that the superconducting temperature of 4 K is uselessly low. That's true, but beside the point.

The point of superconducting graphene is not to use it as a general purpose superconductor where the goal is to have the highest Tc possible. The point of superconducting graphene is that graphene's electrons flow in a way that's very different from most materials.

In most materials, if you apply a voltage, the electrons will speed up (F=MA, Newton's second law). This how a voltage drives electrons into your computer.

However, because of its crystal structure, graphene is different. In graphene, electrons always travel at a constant speed, no slower and no faster. This feature of graphene is also why its electrons are sometimes called massless (despite not being truly massless). Their motion is analogous to photons, which always travel at a constant speed. And because these electrons travel like photons instead of electrons, it has a bunch of consequences in solid state physics and electronics.

The importance of superconducting graphene is that we now have a new variety of superconducting electrons to study.

How does this constant velocity / "massless motion" affect the parasitic inductance of the material ( if at all) ?

Regarding:

>it has a bunch of consequences in solid state physics and electronics.

Are these consequences purely in the realm of theory at the moment? Or do we have some idea of why they might be desirable/interesting now?

Does this mean that the electrons experience infinite acceleration? I know very little about graphene, but this seems to violate some basic laws of physics. Do the electrons actually behave this way? Or is this description of constant velocity electrons simply a close approximation/good analogy for what is actually happening?

If anyone would like to read the journal article, it can be downloaded from library genesis.

http://libgen.io/scimag/index.php?s=10.1021%2Facsnano.5b0784...

good site! thanks

Well... fortunately we have arXiv for open access e-print repository. This is what you should quote:

http://arxiv.org/abs/1508.07079

I don't know if you are aware of this but there are many scientists out there that do need the site you've mentioned in order to function. This kind of exposure is going to kill their chances sooner than expected. The first rule of Fight Club is: You do not talk about Fight Club.

I must disagree. Unlike it's predecessors, such as textz, gigapedia, and library.nu, (these are from before my time, so correct me if I'm wrong), library genesis is healthily mirrored, and everything is torrented. Any attempt to assail it will simply ensure its resilience in my opinion.

4K is not very useful, but it is progress non the less.

https://en.wikipedia.org/wiki/List_of_superconductors

Highest listed there 39K https://en.wikipedia.org/wiki/Magnesium_diboride Doesn't mention others at https://en.wikipedia.org/wiki/High-temperature_superconducti... like https://en.wikipedia.org/wiki/Hydrogen_sulfide More at https://en.wikipedia.org/wiki/Room-temperature_superconducto...

Do we know enough about physics at the atomic level to be able to predict and simulate these combinations of materials? Or do we still have no clue and it's left to experiment to be able to validate material design?

Well, we know a lot about the crystal structures of several high-temperature superconducting compounds. You could always make an educated guess of a new one based on these and then test it for the Meissner effect.

At a low enough temperature (< 4K) ...

I thought there were already demonstrations of superconductivity in graphene at higher temperatures with other dopants (I think water IIRC).

Well, this effect was discovered last year http://cleantechnica.com/2015/09/10/single-layer-graphene-su... (at ~5K). The new breakthrough seems to be in manufacturing.

Even Lead is superconductive at 7.2K.

Someone explain this to me like I'm an undergraduate in Physics, why is this significant then, just because it is Graphene?

Metal just conducts while a semiconductor is like a switch that you can turn on and off. Since graphene is a semiconductor it is more useful for creating faster devices such as transistors.

A fair number of semiconductors superconduct too (such as SrTiO3). The notable thing about graphene superconductivity is graphene's electrons, not its ability to semiconduct. Because of graphene's crystal structure, electrons propelled by a voltage will travel at constant speed, rather than accelerating. In this sense, the electrons are 'massless' (photons are massless, so they always travel at the speed of light and cannot be accelerated).

>electrons propelled by a voltage will travel at constant speed

You mean like Ohm's law with a constant electric field?

No, not like that. When electrons travel in a regular conductor, they have a distribution of speeds. Ohm's law just describes their average behavior.

Just in case I misunderstood your question, I will say a few more things:

Ohm's law applies to both graphene and regular conductors.

In graphene, electrons have only one speed, but they can still move in any direction. In a regular conductor, electrons have many speeds and move in any direction.

In either case, with no electric field applied, the average velocity of electrons will be zero. But with an electric field applied, the average velocity of electrons will be non-zero. And in both cases, the average velocity is proportional to the applied electric field, meaning that the material can be described by concepts like resistance and electron mobility.

The key difference is that graphene has electrons with one speed and a distribution of directions, whereas regular conductors have electrons with a distribution of speeds and a distribution of directions.

I thought graphene isn't a semiconductor? I mean it probably depends on topology, but by itself graphene conducts electricity very well.

The electrons in the graphene take on a special shape where they behave as if they had no mass. This means they can travel at a high speed and gives graphene its high electrical conductivity. That coupled with the superconductivity make the prospect of a tiny high speed computer possible. The other piece of importance was the manufacturing process used which will make it easier to manufacture and study graphene hopefully increasing the rate of understanding.

Lead is a metal, graphene is a zero band-gap semiconductor. Very different electronic behaviour.

Psh, Jan Hendrik Schön showed in 2001 that carbon is superconducting at high temperatures. Just kidding; he was a fraud, but it's a fascinating story: https://en.wikipedia.org/wiki/Schön_scandal

Totally fabricated and the other authors suffered no consequences.

Ignorant question but could this be useful for companies like D-wave who are trying to build quantum machines? They're cooled to well below the superconducting temperature as it is.. I guess I'm not sure what function the graphene semiconductors serve.

When I read the title I thought at first it was new marketing speak for a startup cashing a humongous funding round.

The temperature of deep space is 2.7K, so could these low temperature superconductors have easier application there?

Can someone please Explain This Like I'm 5 - The potential Graphene has when compared to the Lithium batteries we have in the market today, and if Graphene is going to make it's way into our batteries any time in the near future?

Thanks

-- EDIT --

Pardon my ignorance! It seems I was very confused about the topic in question, and mistakenly asked about super capacitors. Thanks for pointing it out!

Just to be sure, first, are you clear that your question has nothing to do with the article in question? Calcium-doped graphene superconducting at 4K means nothing for your phone battery.

The article isn't about energy storage, it's about graphene superconductivity. When it becomes superconductive, it allows the free flow of electrons without resistance which produces heat. One of the limiting factor of today's chips is heat dissipation; if no heat was generated, we could make them higher clocked and faster.

I think this is not linked with battery storage. Superconductivity allows a material to conduct electrons without any resistance, thus losing less energy and generating less heat. I could be wrong though, I am no expert.

You can use superconductors for energy storage. An inductor stores energy, but can not be used for long-term energy storage due to resistance. A superconducting inductor can be used to store energy, as there is no loss due to resistance.

https://en.wikipedia.org/wiki/Superconducting_magnetic_energ...

You might be thinking of supercapacitors, which store energy. http://physicsworld.com/cws/article/news/2010/nov/26/graphen...

My prediction for the year 2100: many more articles about graphene, little to no real world usage growth.

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