Friday, January 17, 2014

\(Na_3Bi\), a three-dimensional cousin of graphene, discovered

Synchlavier, a FB contact of mine, has focused my attention on a Berkeley Lab press release:
Natural 3D Counterpart to Graphene Discovered:
Researchers at Berkeley Lab’s Advanced Light Source Find New Form of Quantum Matter
It promotes an October 2013 experimental paper
Discovery of a Three-dimensional Topological Dirac Semimetal, \(Na_3Bi\) by Z.K. Liu and 11 co-authors (arXiv, PDF, APS meeting)
This unusual molecule involving sodium and bismuth is claimed to have similar, but three-dimensional, properties that make it a higher-dimensional counterpart of the miraculous two-dimensional carbon-based material called graphene (one layer of hexagonal carbon atoms).

The material is the first example of a three-dimensional (3D) topological Dirac semi-metal (TDS, so 3DTDS if you combine the acronyms) that may be interpreted as the critical point in the transition between a regular insulator and a topological insulator.

At this special point, the material has many unusual properties. For example, the electrons have a much higher velocity and mobility. If you don't know, electrons' speed in graphene is 100 times higher than in silicon. See some values of velocity and mobility in silicon. Just to be sure, we often talk about the mobility \(\mu\) which is the coefficient in front of the electric field \(E\) in the formula for the drift velocity \(v_d\)\[

v_d = \mu E

\] which implies that the units of \(\mu\) are \({\rm cm}^2/({\rm V}\cdot{\rm s})\). You may calculate the velocity for the electric field \(100\,{\rm V/m}\), for example.

Although some functions of the circuits don't really depend on the drift velocity (which may be really, really low), it's still good to have a higher drift velocity so it's a good guess that the new class of materials might be helpful in speeding up the microprocessors and similar chips. The material's better magnetoresistance makes it ready for dramatic improvements of the classical hard drive. And other properties make it a candidate for good new optical sensors.

If you don't know how to think about graphene to realize where its remarkable properties come from, don't worry. Sheldon Cooper had the same trouble despite his IQ 187. But he got it, see 2:59 of the video above. See also his failed attempts to visualize the physics of graphene that involved colorful balls. ;-)


  1. I think that it was Steve Giddings.

    No, I disagree. I think it's an intellectually shallow, ideology-driven effort that is unlikely to succeed because any direct - at the current level - test of any theory of quantum gravity probably requires unrealistically extreme energies etc.

    I know roughly which experiments he talks about and these ideas are mostly misguided but a separate discussion would be needed for each.

  2. Nope, it was Steven Gubser commenting in Sabine's post "shooting strings"; if you believe it the kind of experiments he was talking about were related to QGP.

    QGP cannot justify String theory! And we are talking about Steven Gubser here with numerous contributions in String theory. Sometimes I don't understand how people think.

    Such statements make me angry.

  3. Yep, that post on Backreaction was annoying ...

    You and Cliff made quite a good stand ;-)

    Steven Gubser's comment I did not yet see, will have to check it ...

  4. As a solid-state physicist this is a really exciting development. Aside from the speculated applications there are likely to be uses as yet unimagined.

  5. I'm currently indisposed. Sorry about that. I blame it on the Eyeties — it's their Peroni.

    Meanwhile, if you want to know anything technical, especially about the universe, or any other aspect of reality, please ask Luboš. He deputises for me while I'm 'away' — he's pretty good. He seems to be up to speed on most things.

    However, he is still very young, and hasn't quite mastered the Bolloxian Dialectic. But then I suspect he never will. Indeed, I think he might be a Goy!

    Am I bovvered [by that]? Well, am I?

    Answers on a postcard to ...


    Banning countdown: 10, 9, 8.9999999, 8.9999999-ε...

  6. Wow. I would think twice before ringing at your door ;-)

  7. Years ago, I met a cop who told me that whenever he goes to answer his door, he's armed. He said, "It's incredibly effective at separating the legitimate from the illegitimate."

    I doubt that Werdna is right with "presumption," but this is pretty technical and I'm not sure. The police would try to figure out whether she was in genuine fear of death or serious injury. I think she'd lose if she said, "I presumed ...," at least in some jurisdictions.

  8. Dear Shannon, Dieudonné is not a humorist but a vile hater.

    I agree with you, however, that curtailment of free speech is not the answer.

  9. I know Eugene. However he should have the right to say whatever he wants in his shows. If people don't like him they don't go and see him full stop.

  10. Well, that's what I said, isn't it? ;)

    But read the interview with Gaspar Koenig; using the courts as a club to silence someone is not new in France. Even Marine Le Pen does it.

  11. I'd say she would have difficulties to prove the guy's intentions if she shoots him before he tries anything. It's tough but that the way it is in law.

  12. Well Eugene it doesn't seem to me we agree here ;-). When does Marine Le Pen uses courts to silence someone? When judges in France are rating all politicians and journalists on their "mur des cons" it is precisely to silence someone in agreement with their Union.

  13. If you're unlucky, the people breaking down your door at 3 a.m. will be police conducting a "no-knock raid" that was supposed to target your next-door neighbor the suspected drug dealer. Bleary-eyed and sleepy, you don't recognize their uniforms and unload a S&W .38. In court, the cops all swear that they loudly identified themselves as police... and you get sent away for 25 to life. (This has actually happened.)

  14. From the interview:

    Marine Le Pen a promis d'attaquer pour diffamation quiconque la qualifie "d'extrême droite"

    My French is not too good but I translate that as "Marine has vowed to slap anyone with a lawsuit for defamation who calls her an extreme right-winger".

  15. It's a good approach - of course, an important question is whether she will win the lawsuit. ;-)

    I have never had anything to do with courts but some of these libels seemed tempting to me.

  16. Eugene, anyone is allowed to use the law when they feel they are being treated unfairly. I am surprised that you seem to have a problem with this.

  17. Anyone can sue anyone for anything, that's right. But if it's a bad idea to use the courts to silence Dieudonné from spewing his hate, why should it be O.K. for MLP to threaten anyone with an expensive lawsuit who calls her an extreme right-winger?

  18. She can threaten but the Law will decide who is right. In the case of Dieudonne the local court ALLOWED him to run his shows in the name of "freedom of speech". It is only by a never-seen-before intervention from Manuel Valls that his show was forbidden an hour the start.

  19. Valls couldn't unilaterally decree that, he had to go before the highest competent court in the land and the court agreed with him. So the "Law" in France says it's o.k. to curtail free speech. I think that's a problem. Likewise, I think it's a problem if MLP can have a reasonable expectation that some court will grant her relief if she charges someone with defamation for nothing more than calling her an extreme right-winger. Defending against such a charge can easily set you back ten thousand euros. You may get lucky and be supported financially by some free-speech advocacy organization, but it's nothing you can count on beforehand.

    I would prefer that people engage in argument, not litigation or the threat of it. Unfortunately that does not seem to be a popular viewpoint in France. The Liberal Democrat Party in France, whose page advocating free speech I linked to, does very poorly at the polls.

  20. Dieudonné indeed is a disgusting anit-semite, of the same kind as Julius Streicher ( ), William Joyce ( ), Céline (éline ) and others. Note that the first two were hanged, although they never killed anybody or did anything in any way different from what Dieudonné does, and the third one was sentenced to one year in prison in absentia (having escaped from France), even though he was one of the greatest French writers of the 20th century and did not actually directly collaborate with the Germans (except for stating many times that they were “too gentle” in their treatment of the Jews and continuing to deny the Holocaust.

    Dieudonné has done everything that these three have done and in addition he is a fellow traveller of the far left, the very worst Islamists and, significantly but not surprisingly, of the supporters of Le Pan. Common hatred makes for strange bed companions.

    However, while I have no problem at all with the handing of Streicher and Joyce (I would not have done that to Celine, but for reasons that would take to long to explain) I would not be in favour of doing this to Dieudonné. Or rather, the relevant question is, whether France is now at peace or at war. If it is at peace than even Dieudonné is entitled to free speech, but then so are all those people who want to burn the Koran on the streets of Paris - which would greatly upset the great majority of his fans. If however France is at war with the Islamists, then he is a traitor and should be treated accordingly. The problem is the French are unable to decide whether they are at peace or at war although sooner or later they will have to.

    By the way, Dieudonné is, of course, like Celine and an unabashed Holocaust denier. So this brings up the issue: should Holocaust denial be illegal? Well, being a strong supporter of free speech I believe that any kind of historical or scientific “denial”, however idiotic or disgusting, should be legal. I don’t think the state should ever intervene in such cases. However, I also believe that you cannot go around slandering people in most disgusting ways without facing the consequences. Holocaust denial involves slander of the worst kind against an enormous number of witnesses, many of them still alive. It implies that they are the worst kind of liars and if believed would be a huge blot on the reputation. In most countries slandering people publicly in this way will lead to a court suits, in which if the victim can prove his case, the culprit will suffer heavy financial consequences. In my opinion victims and families of victims of the Holocaust should be able to sue people like Dieudonné, and if they can prove their case, the consequences should be the same as in other cases of very serious defamation. But this should not be an issue in which the State is involved directly.

    Finally, now that the issue of anti-semitism has come up again, I can’t resist the temptation of a little black humour:

  21. Regretfully, I do not agree with you. As tempting as it is to continue this conversation, I have to get back to work so will have to bow out at this point.

  22. MoptopTheLibertarianJan 18, 2014, 1:56:00 PM

    They define species pretty generously these days. For instance, a polar bear that hunts on the ice and lives on seals is considered a different species than a polar bear that hunts on land and lives on salmon, for example. So a polar bear could actually change species during its lifetime.

    I don't know the particulars of your case, but they also are pretty careless with mouse species too, basically, a city mouse and a country mouse can be considered different species even if genetically identical based on cultural grounds.

  23. Engineering is things, chemistry is stuff. Things can be manufactured and sold, PERT-charted and on spec, so engineers are management darlings. Stuff is very different. Stuff is dirty, risky, and paradigm-shifting (Stephanie Kwolek, you just wouldn't let go, would you?). Scientists are insubordinate pains in the ass. Eject the scientist, keep the stuff.

    Na3Bi threatens to bollox graphene investments. Cd3As2 threatens to bollox Na3Bi. Synthetic organic architectures have never been "interesting" conductors. Perhaps an undergrad screwing around will stumble on upone, as BCS heresy MgB2 was discovered by disobeying orders, and polyacetylene synthesis was a cgs/mks error.

  24. Forget shooting the ones coming for your air conditioning. Just shut off all fossils fuels to them. No oil, no natural gas, no gasoline. See how far they get with wind turbines and solar panels.

  25. Speaking of solar/pattern climate.
    What can be done about the mini ice age? Are we going to see AGC alarmists groups forming?

  26. Is everyone assuming I am a woman?

  27. I wouldn't know about others but for what it's worth to you I have been unconsciously assuming you are a man, and that's despite the 'a' at the end of your name, which is new to me. I simply took it as a pseudonym.

    By the way, you never struck me as being backward, even though your question has only now prompted me to see the possibility. ;)

    Maybe you're made of antimatter? Is that it? :)

  28. I thought you were a man but then SmokingFrog said "she"... Since you don't say I am now thinking that you are androgynous. But then I wonder about androgenes psychology towards guns, and justice, in Florida...?

  29. The problem in France is that it is always only one side who is willing to engage in argument. The other side (government, media) have enough power to avoid any subjects they want ignore. That's why these days we have all the buzz about you know what with Hollande, then Dieudonné etc... It is buying time before two crucials elections coming up. More revelations are soon to come out, this is good for the government, and always enjoyable for the journalists.

  30. Well, I looked up Werdna on the Internet and found that he (yes, he) was a evil wizard.
    Everything seemed to fit ;-)

  31. Well, such differences can be sometimes very interesting and are not well understood. One of the most curious is that between the so called "transient" killer whales (orcas) and "resident ones". They differ primarily in their diet: the residents eat only fish (even sharks) while the transients never touch fish and eat seals, sea lions, dolphins, even , very rarely, swimming polar bears (however amazing that might seem). It's not know if the two kinds of orcas should be considered the same of different species but they don't interbreed and have not done so for a couple of million years.

  32. When Germany and Austria passed laws criminalizing holocaust denial, the aims were noble. Legislators recognized that the spreading of falsehood about this very well documented chapter of history not only did great injury to survivors. It also prepared to make future genocide possible by exculpating the perpetrators of the previous one. They thought that not only would a prohibition of holocaust deniaö help to make a repeat of a genocide of Europe's Jews impossible, it would also help to forestall future genocides of any peoples, anywhere. The aim was to eradicate antisemitism and similar hatreds root and branch by criminalizing their worst manifestations.

    The reality has turned out different. Hatred of Jews is alive and well in Europe and some other parts of the world. It is not a worldwide phenomenon -- for example, it is unknown in China and India -- but many Europeans and especially Muslims will never let go of it. It serves their needs too well. The laws against holocaust denial have stirred up resentments about "special treatment" for a "favored group" and prompted critics to complain of infrignements of academic freedom and free expression, often disingenuously.

    Sadly, the noble experiment has not proceeded as hoped for. The time has come, in my opinion, to repeal the failed laws. There are other ways to combat holocaust denial than through the courts. When it comes to involving the state, I make no distinction in principle between a criminal prosecution and a civil action in tort for defamation: both make use of the court system, which is a function of the state par excellence. In a civil society where enough people are fundamentally decent, it should be sufficient to shun holocaust deniers: do not buy their books, do not attend their readings, and express strong disapproval of people and organizations who patronize them by withdrawing your friendship and custom. It's not a guarantee of preventing another genocide, but no such guarantee can be had.

  33. Hi, all,

    I just published a popular article (at least, I hope it will be popular) on the new 3D topological Dirac semimetals - . If you want to read a bit more about the discoveries, hhave a look on me!


  34. nice short summary, thanks!

  35. Fact is that presently research is cut to only short term projects that's "immediately" get profit. Fact is that in history each big discovery were with big rank of fortuity. I am big fan of string theory, it makes me nervous that almost no alternative for it and no support of String theory at all.

  36. ConsiderMyselfAsAScientistFeb 16, 2014, 10:52:00 PM

    Scientific theories need to be falsifiable: but they aren't actually!! For example, no one has a few billion dollars to replicate the experiments by CERN and so to test them...this is not science...