Tuesday, January 14, 2020

The Wolf Prize and how condensed matter physics works

The Wolf Prize in Physics for 2020 was announced yesterday, and it's going to Pablo Jarillo-Herrero, Allan MacDonald, and Rafi Bistritzer, for twisted bilayer graphene.  This prize is both well-deserved and a great example of how condensed matter physics works.  

MacDonald and Bistritzer did key theory work (for example) highlighting how the band structure of twisted bilayer graphene would become very interesting for certain twist angles - how the moire pattern from the two layers would produce a lateral periodicity, and that interactions between the layers would lead to very flat bands.  Did they predict every exotic thing that has been seen in this system?  No, but they had the insight to get key elements, and the knowledge that flat bands would likely lead to many competing energy scales, including electron-electron interactions, the weak kinetic energy of the flat bands, the interlayer coupling, effective magnetic interactions, etc.  Jarillo-Herrero was the first to implement this with sufficient control and sample quality to uncover a remarkable phase diagram involving superconductivity and correlated insulating states.  Figuring out what is really going on here and looking at all the possibilities in related layered materials will keep people busy for years.   (As an added example of how condensed matter works as a field, Bistritzer is in industry working for Applied Materials.)

All of this activity and excitement, thanks to feedback between well-motivated theory and experiment, is how the bulk of physics that isn't "high energy theory" actually works.  

17 comments:

Henry Axt said...

In relation to the last comment:

What do you think have been the main driving forces between the differing evolution of the fields of condensed matter physics and HEP? Do you think it is fundamental to the physics of the field, or fundamental to the "culture" of the disciplines?

Jay said...

Doug, I'm interested in a little more insight into what you meant by

"(As an added example of how condensed matter works as a field, Bistritzer is in industry working for Applied Materials.)"

Because, it doesn't seem like Bistritzer is NOT working on anything remotely related to the work the prize is for, or graphene, or even materials, for that matter. He's working on computer vision and machine learning algorithmic research.

Could you elaborate on what you meant by your above comment ?

Douglas Natelson said...

Henry, I think the scale of experiment is a major factor. Traditional accelerator-based physics is (in recent decades) a huge endeavor requiring multidisciplinary teams of hundreds if not more, extremely complex facilities, and necessarily a completely different kind of planning cycle than condensed matter. For the energy frontier of HEPX, the LHC is the only game in town, with two major detector collaborations. Contrast that with condensed matter, where experimental teams are much smaller and many more groups are able to jump in and realistically contribute on pending problems. HEP theory has the problem that many of the mechanisms they are postulating are inherently at energy scales incredibly hard (or presently impossible) to access in experiment or observation. In condensed matter theory, one of the first questions about any new theoretical idea is, how could we test this experimentally?

Jay, perhaps I was too careless in my wording. I know he's working on machine learning stuff, but I do think it's interesting that there is an industrial connection at least nominally connected to materials.

Anonymous said...

For the kind of work that Bistritzer is doing at AMAT, I suspect that someone with a high energy physics background who does a lot of data analysis would be equally suited. It's not like he is working at an industrial lab like Bell Labs or IBM Research where he gets to use his condensed matter background.

Anonymous said...

It's a bit bitter sweet to see Bistritzer get the Wolf prize. He did all the hard work to get this prestigious award, but didn't get a faculty position and ultimately left condensed matter research for industry.

Anonymous said...

If you read "news" on HEP from people like Woit/Hossenfelder who don't contribute meaningfully to the field and write blog posts instead of research papers, than good luck to you.

"HEP theory has the problem that many of the mechanisms they are postulating are inherently at energy scales incredibly hard (or presently impossible) to access in experiment or observation. .. one of the first questions about any new theoretical idea is, how could we test this experimentally?"
This is what hep-pheno pretty much is all about - and still people complain.. The problems are just very hard, but this doesn't mean there is no progress. People look all the time at new signatures and propose detectors. Some even got funding already. Remember there will be also High Luminosity era of LHC.
Look eg. at https://arxiv.org/ftp/arxiv/papers/1903/1903.04497.pdf for LHC alone and in general at latest 2019 PBS group review: arXiv:1901.09966 to get a clue.

Douglas Natelson said...

Anon@4:48, I'm not throwing any stones at high energy phenomenologists, and I appreciate that there are a bunch of people working hard on how to find detectable signatures of interesting physics at the LHC and its future upgrades. I know the HL-LHC will be turning out enormous volumes of data into the 2030s. The more out-there characters, though, some of whom are actively arguing that testability is not a big deal, do seem to be the ones in the public eye a lot, rather than the hep-pheno folks. I appreciate that this is a sensitive topic - any flippancy on my part is from accumulated years of seeing "physics" used in the public space as if it comprises only hep theory.

Anonymous said...

Anon@4:48, Woit and Hossenfelder's extremely meaningful and crucial contribution to the field is that they lay bare the degree to which a section of it has turned into religion, replete with popes, ayatollahs, archbishops, etc. I suggest you read carefully the following: https://iai.tv/articles/why-physics-has-made-no-progress-in-50-years-auid-1292

Anonymous said...

Douglas Natelson: I am Europe based, where - I believe - most of hep-research has at least some pheno flavour. I don't work in hep-th but i interact with some of those folks and none i know expressed view that "testability is not a big deal".
Some prominent US seniors from hep-th said that or they hype their research as 'final-theory' or some other irresponsible stuff to journos and than demagogues portrait the whole field as brain-dead because those claims don't hold up. But press is full of stories of new Einsteins etc. - the journalists are in general clueless about physics. What is really worrying is that those demagogic claims of dead-end in hep are repeated by other PHYSICISTS - you literally linked post which title contains phrase "no progress in * years". Now that is dangerous.



Anon@5:46: I don't know if you are serious or trolling - i linked 2 RESEARCH papers which contradict the claims from article you linked - and they represent very specific search strategy, by no means exhaustive of the depth of the field. The same persons you mentioned were also saying how funding new experiments are a waste of money. So basically they complain no matter what is proposed, while they don't do research themselves.

Two links with rebuttals from twitter to Woit and Hossenfelder (i'm sure there are plenty but I don't want to waste any more time on these individuals):
hep-th:
https://twitter.com/nu_phases/status/1217161859435921408
hep-ph (Hossenfelder is not only against new collider - which admittedly would be very pricy so it's not so clear-cut - but also against any new small - here dark matter - experiments, basically because they can't guarantee results):
https://twitter.com/gfbertone/status/1144342295103324160

Douglas Natelson said...

Anon@8:28, I greatly doubt that my linking anything is dangerous, and I am a snarky person - mea culpa. There certainly is some amount of poor journalism about this topic, and dramatic headlines sell books/papers/clicks.

Anonymous said...

Tragic but rather expected that the insiders are blind to what is plain to see for anyone outside the field.

By the way, Anon@8:28, you have some nerve suggesting that posting a link to a piece that you disagree with is "dangerous". GTFOH, you and your righteous indignation.

Then again, that's something right out of the "The Good Mujahid" book. Only omission: you forgot to scream "TAKFIR!" in conclusion.

Anonymous said...

Anon@4:40, I agree with you that the fellow at 8:28 is out of line, but I feel that your vitriolic language, particularly in the last paragraph, comes off as derogatory and offensive.

Anonymous said...

Anon@2:38, that was the intent, exactly. May I suggest you develop a thicker skin? Zealotry and fascism, in science or elsewhere, are not countered with flowers. Still, vitriolic language is a mercy compared to fuming vitriol, which is recommended in Chapter 29 of the same book "What to do if woman or infidel does not conform after repeated beatings."

Seriously now: It is a sad spectacle to see the ad hominem attacks and ridicule that a few brave souls have to suffer for simply articulating a critical re-evaluation of a field of science, which of course has potential to affect scientific livelihoods, reputations, and funding streams. They have my support where and when I can offer it.

Douglas Natelson said...

Knock it off. It has been years since I had to delete offensive comments on here, but any more that sound like attacks on a religion and I will do so. You can make your point without imagery from religious texts or the language of persecution.

Anonymous said...

What on earth is going on in these comments??

Anyways, Douglas, what do you think of thre comparisons made between TBG and high temperature copper oxide superconductors. Is this comparison warranted? Or is something fundamentally else at play?

Douglas Natelson said...

Anon@8:25, I want to be cautious as these are still early days yet. There is surely a superficial resemblance (two-dimensionality; superconducting states appearing as the system is "doped" away from commensurate filling factors where the system is instead insulating; some indications of unusual resistivity temperature dependence in the normal state above Tc; arguments that scanning tunneling spectroscopy shows the importance of e-e interactions in this system). However, the system is microscopically very different (completely different lattice symmetry; multiple bands and the importance of orbital effects and topology b/c of the valley degeneracy), and various mechanisms for superconductivity have been proposed. The similarity may be this: When bands are very flat, there generically ends up being many competing types of order, and superconductivity may generally be in the mix.

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