Tuesday, October 29, 2013

Accusations of misconduct regarding a condensed matter paper

I had heard some gossip about this from a couple of my colleagues last week, and now it would appear that the news has broken in the English-language media.  The paper at hand is this one, which reports that, in one of the iron pnictide superconductors, there can be phase separation between regions of one composition (K0.68Fe1.78Se2) and regions of another composition (K0.81Fe1.6Se2).  This is important because in trying to understand the superconducting properties of samples with some nominal composition, it's a big deal to know whether you're looking at a homogeneous system or one where some other composition is actually dominating the properties.

The accusation is reported here and here, and comes from Prof. Mu Wang at Nanjing University (also the home institution of the accused, Prof. Hai-Hu Wen).   There are at least two scientific ethics issues.  First, there is a question about co-authorship (did all of the authors on the paper actually contribute, and did they even see the paper prior to submission).  Second, from what I can gather, there are concerns about data selection in Fig. 4 of the paper.  People who know more about this, please feel free to chime in, since it's a good idea to understand specifically what the concerns are regarding the validity of the scientific claims of the article.  The added dimension to all of this is the claim that both the accuser and the accused were up for membership in the Chinese Academy of Sciences (though apparently the accuser has withdrawn his candidacy - see my second link in this paragraph).  Interesting, particularly since accusations like this in the physical sciences remain relatively rare.

Sunday, October 27, 2013

Two striking results on the arxiv

This past week, I noticed two preprints on the arxiv that particularly got my attention.

First, "How many is different?" In condensed matter physics, we like to point to Phil Anderson's famous 1972 paper "More is different" (pdf) as an important tract about the nature of our field:  Fascinating, rich, profound physics can emerge from collective, interacting, many-particle systems.  As I've said before, one water molecule is not wet.  A large ensemble of water molecules can be.  The preprint at hand looks specifically at a classic statistical mechanics problem, the ideal Bose gas, and summarizes results that show that it takes, for a cubic box, exactly 7616 particles for there to be a real thermodynamic liquid-vapor-like transition.  (Note that in this case there are no interparticle interactions; it's the identical nature of the particles that leads to this effect.)   A spherical box would lead to a different criterion.  Still, it's pretty neat to me that sometimes we can come up with a direct answer to "how many particles does it take before we see an emergent collective response?"

The other paper is "Reaching Fermi degeneracy by universal dipolar scattering".  Truly cooling the atoms is a major challenge in the trapped-atomic-gasses community, particularly those people who want to use optical lattices filled with fermionic atoms as a way to simulate electronic phases relevant to condensed matter.  A phenomenon called "Pauli blocking" is a real hindrance.  As a Fermi gas cools, there are fewer and fewer empty single-particle states into which you want to scatter the excited ("hot") atoms.  (Fermionic atoms can only get into empty states, because the Pauli exclusion principle forbids multiple occupancy.)  These authors are able to leverage magnetic dipole-dipole scattering within a cloud of erbium atoms to get to temperatures below 0.2 times the Fermi temperature - quite cold for these folks.  If this can be adapted to other systems and optical lattices, that would be very exciting.  (For reference, room temperature is something like 0.005 times the Fermi temperature of copper, and lots of exciting solid state electronic physics requires such low temperatures.) 

Friday, October 25, 2013

Follow-up: Workshop on "Surface Plasmons, Metamaterials, and Catalysis"

The workshop here was, I think, very successful.  It was great to get so many knowledgeable people together in one place to talk about these issues.  Here are some key points that I learned from watching the talks and speaking with people:
  • While it may take years and $$ to build, single-molecule tip-enhanced Raman spectroscopy in variable-temperature UHV looks like an amazing capability.  Turns out that vibrational lineshapes that look gaussian at room temperature look like Lorenztians at cryogenic temperatures, as one would expect for true (not inhomogeneously broadened) resonances with well-defined lifetimes. 
  • It's possible to get large electromagnetic field enhancements out of high-index materials even without plasmon resonances.  Clearly it is worthwhile to try to create geometries where the local high intensities occur close enough to a surface interface that charge carriers produced there are able to diffuse to the surface to do chemistry.
  • Careful engineering of structures can lead to very high (say 90%) absorption even in extremely thin coatings.  That is, you can imagine making anti-reflection coatings that are tuned to produce absorption in materials where the loss mechanism can be used to do chemistry.
  • By driving plasmon resonances detuned from the resonance, it is possible to favor net motion of charge (generating photovoltages that can be measured in experiments).  Conversely, gating structures to alter their total charge density can tune their plasmon resonances (though it's still not clear to me how one would make this a big effect).  Shifting the energies a little with charge is something I understand; drastically changing the intensity of the resonances with charge is much more mysterious to me.
  • Very specific defect sites can drive very particular catalytic reactions.  In some special cases theory can show how this works, but I can't help thinking that there are many issues left to resolve.  For example, in discussing catalysis most people draw energy level diagrams, correctly showing that energy conservation is really important when, e.g., a hot electron in some solid is able to occupy (transiently) an unfilled molecular orbital in a molecule of interest.  However, there are other issues that affect which electronic processes can happen (e.g., momentum conservation; how incoherent hot electrons or holes can excite plasmons, which are coherent e-h excitations) that seem to be given short shrift.
  • When an electron transiently occupies an empty molecular orbital, you can think of that as delivering an impulse to the molecule's nuclei.  (The equilibrium bond lengths differ when the molecule has an extra electron; thus passing through that state is like kicking the nuclei.)
  • Single-particle vs. ensemble studies (via plasmons and optics) can give insight into processes like the evolution of phase transitions with size - such as the formation of palladium hydride.
  • Doped Si can support nice plasmon excitations out in the mid-far IR, and could be very interesting from several points of view.
  • While it's very trendy to worry about water splitting, there are a huge number of other reactions that are important and complicated!  For example, converting CO2 to methane is eventually an eight electron process (!).
Those are just a few points.  Teaching, etc. made me miss some of the talks as well.  All in all, good talks and good discussion.  There is clearly an enormous amount still to be done in this field, both on the experimental and theory sides.

Monday, October 21, 2013

Workshop on "Surface Plasmons, Metamaterials, and Catalysis"

Today is the beginning of our workshop on "Surface Plasmons, Metamaterials, and Catalysis", hosted here at Rice.  I've mentioned this before; it's actually happening, and thanks to the end of the government shutdown, the ARO sponsors are even going to be able to see the talks.  Should be fun, and I'm hoping to learn a lot.  As I've said previously, catalysis seems like magic to me sometimes.  I'll try to post a bit about what I learn.  (By the way, this is the 702nd post on this blog.  Meant to point out the Big Round Number threshold last week.)

Wednesday, October 16, 2013

How to: write a scientific paper (in physics, anyway)

There are many resources out there for people who want guidance on scientific writing.  Here, in very brief form, are my tips.
  • First, do some science.  That sounds flippant, but in order to justify adding to the scientific literature (assuming we're talking about a research-based paper here and not a review article), you do have to have done something.  Figuring out really what you've done and being able to articulate it clearly in a couple of sentences is essential.  What do you know now about physics that you did not know before the work?  Compelling papers are stories - they have some narrative structure (more on that below).
  • Who is your audience?  Remember that you would tell your story differently to a specialized audience (e.g., your direct competitors who already know the topic in depth) than you would to a generic physicist in your subfield, and still differently to a generic physical scientist (if you're aiming for a broad/glossy journal).  This is equivalent to figuring out at least in rough terms where you are going to submit the work.  Knowing your audience gets you in the right frame of mind to....
  • Figure out your figures.  Ok, so you've done some piece of physics.  How can you explain that in images/graphs/visualizations?  For a short "letters" paper, it's typical to have around four figures.  Often the first figure somehow sets the context and may include a cartoon/diagram of the setup or the system.  The figures need to tell the story in a logical way - if you're an experimentalist, show what you measured, and show how you got from those measurements to your conclusion (characterizing a new phenomenon?  Comparison with some candidate models?).    Again, who is going to be reading this - a specialist, or someone who needs some intro context?  Work hard on your figures - many readers will spend far more time looking at your figures that sifting through the text.
  • Tell your story by describing the figures.  As I said, a paper is a narrative, but unlike historical literature you are not required to describe what you did chronologically, and unlike detective stories you do should not leave the main point for the very end.   If you've chosen your figures well, you are now something like 80% of the way there.  Do not worry about length at this point.
  • Now work on the intro and the conclusions.  The intro needs to reflect the Big Picture and place your work in context, while citing appropriate literature references.  In a short paper, you don't need to cite everything remotely related to your work, but you don't want to leave out major contributors.  Don't cite yourself unless it's really germane.  The intro is where you will gain or lose the audience, including reviewers.   Usually at the end of the intro is a paragraph that starts out "In this work, we...."  That's where you need to be able to hit the highlights of your work in just a few sentences.  Really work on your intro.  It's right behind the figures and the abstract in terms of making an impression on the reader.   As for conclusions, what you do here depends on the journal.  Some journals just don't do concluding paragraphs.  Others wrap up the discussion, summarize the results again briefly, and then give perspectives on possible future work.
  • Lastly, do the abstract (though I often rough one out earlier).  Again, the abstract needs to be concise, clear, provide context, and summarize the main points of the paper.  As annoying as it is on some level that there is an algorithm for this, there really is, and it works.  Take a look at the Nature guide for writing an abstract (pdf!).   The general format and the way it makes you think about what each sentence is doing can be very helpful, even when generating abstracts for non-Nature journals.
  • Now edit.  Read and re-read the paper, rewording things to make them more concise and clear.  Put it aside for a day or two and then look at it with fresh eyes.  Make sure the coauthors do edits as well.  My approach is definitely to rough some text onto the page and then edit, rather than agonize about trying to write something perfect from the outset.  
  • Think about a cover letter for the submission, and come up with some suggested referees.  For the cover letter, you are trying to convey clearly and cleanly what you did to an editor who has to filter through many many papers.  Don't make it a lengthy exercise.  Do make it accessible, and do make it clear why your work is appropriate for the journal.  On the referee front, don't try to stack the list with your pals.  Pick people who will actually give insights and have relevant expertise.  The editor may well take your suggestions as a jumping off point for picking people out of their database, so if you pick people who have a clue, it increases the likelihood that your referees will be thematically appropriate.
Good luck!  Feel free to add in more suggestions in the comments; I'm sure I'm leaving things out.

Monday, October 14, 2013

Scientific American, blogging, and appropriate behavior

Many out there in the science blogging community have been rightly angered and frustrated by what transpired last week regarding Danielle Lee's blog at Scientific American.  Much as it pains me to link there, Jezebel actually has a cogent summary of what went on.  Short version:  Dr. Lee politely declined a request to guest blog (at a paying advertising partner of SciAm), and was shocked and angered when she was denigrated in sexist, degrading language for her declination.  She posted about this on her blog, and SciAm took down the post, arguing feebly that it wasn't really about science.  This is weak sauce, of course, because SciAm has allowed many of its bloggers to post about topics that aren't directly science.  Pretty much they mishandled this about as thoroughly as possible.

Blogging is a tricky business.  Outfits like SciAm, NatGeo, Wired, etc. clearly value the perspective (and clicks) that bloggers can bring, and must view bloggers as a very inexpensive source of content.  Bloggers generally value the greater readership and exposure that is afforded by a widely recognized host - certainly my readership is much lower than it could be if I blogged for scienceblogs (of course, then I'd feel obligated to post more often).   However, by being independent of these corporate hosts, I have greater editorial control.  I don't have to worry about ticking off advertisers; I just have to keep some level of a lid on my sarcasm and desire to vent. 

This whole thing of course reinforces the standard dictum that seems to be ignored by a surprisingly large number of allegedly smart people:  Beyond trying to be a good person, don't write things in email (or post on the internet) that you would be sorry to see on the front page of the New York Times (perhaps I should say "homepage", since we are approaching the supposed death of print media).  Hopefully someone at biology-online.org (who started all of this with their inexcusable behavior) now appreciates this lesson. 

Monday, October 07, 2013


I have been very busy, and I missed my traditional Nobel guessing game.  To be honest, it seems so highly likely that there will be some version of a Higgs prize (the LHC people have been making preparations for weeks) that it's taken the fun out of matters.  I still hold out for an outside chance of a surprise - perhaps extrasolar planets, or galaxy rotation curves, or geometric phases.  Guess we'll know in about 8 hours or less.

Wednesday, October 02, 2013

Bits and pieces

Sorry for the comparatively slow rate of posts - it's an extremely busy time of the semester, and travel last week threw me off.  Here are a few odds and ends:
  • There is about to be a new edition of Kleppner and Kolenkow, an advanced freshman physics text that I really value.  (Unsurprisingly, when I was taking a class out of it 24 years ago my opinion of the book was not nearly so favorable.)  I'm very much looking forward to seeing the revisions and new problems.  While I like the mathematical sophistication a lot, I think it's superior to most generic freshman books by not trying to distract you on every page with glossy color illustrations and three different kinds of call-outs, text boxes, or tables.  Many modern omnibus books look like they're actively trying to encourage attention deficit disorder.  If they could use the html blink tag and have rotating animated gifs on every page, they would.
  • There is also a new edition of Purcell, a fantastic E&M book.  I've written about Purcell before, and Morin has done the community a great service by revising this book so that the presentation is in what has become the mainstream MKS system of units.   I haven't had a chance to teach out of this new version, which contains more exercises and worked examples, but anything that introduces Purcell's lucid explanations to more students is good.
  • There is going to be a new edition of Horowitz and Hill as well. 
  • The US government took time out from its complete dysfunction last week to address the looming problems related to the strategic helium reserve.
  • I hope the majority party in the US House understands that a US sovereign debt default would be an incredibly bad idea.