Brief items + the March APS Meeting

This has been an absurdly busy period for the last few weeks; hence my lower rate of posting.  I hope that this will resolve itself relatively soon, but you never know.  I am going to the first three days of the March APS meeting, and will try to blog about what I see and learn there, as I have in past years.

In the meantime, a handful of items that have cropped up:

• If you go to the APS meeting, you can swing by the Cambridge University Press table, and pre-order my nano textbook for a mere $64.  It's more than 600 pages with color figures - that's a pretty good deal.  They will have a couple of bound proof copies, so you can see what it looks like, to a good approximation.  If you teach a senior undergrad or first-year grad sequence on this stuff and think you might have an interest in trying this out as a text, please drop me an email and I can see about getting you a copy.  (My editor tells me that the best way to boost readership of the book is to get a decent number of [hopefully positive] reviews on Amazon....)
• On a related note, you should really swing by the Cambridge table to order yourself a copy of the 19-years-in-the-making third edition of Horowitz and Hill's Art of Electronics.  I haven't seen it yet, but I have every reason to think that it's going to be absolutely fantastic.  Seriously, from the experimental physics side, this is a huge deal.
• This is a fun video, showing a "motor" made from an alkaline battery, a couple of metal-coated rare-earth magnets, and a coil of uninsulated wire.  It's not that crazy to see broadly how it works (think inhomogeneous fields from a finite solenoid + large magnetic moment), but it's cool nonetheless.
• Here's an article (pdf) that's very much worth reading about the importance of government funding of basic research.  It was favorably referenced here by that (sarcasm mode = on) notorious socialist organization (/sarcasm), the American Enterprise Institute.

Centers, institutes, and all that

One hallmark of the modern research university is the proliferation of Centers and Institutes, groupings of investigators outside the hierarchy of traditional academic departments.  I'd like to explain a bit about what these entities are, what (in my view) makes an effective one, and some challenges that these organizations face.  There is a great deal of variance across universities with these terms; the version I'm going to describe is mostly what we have at my home institution.  Your mileage may vary, and I'd like to hear your thoughts on what makes a great center or institute.

An Institute is an organization that draws members from across different departments (indeed, often from across different Schools such as Natural Science and Engineering), with a strong, usually broad, thematic focus, and with an annual budget for staff and programs that comes largely from internal university funds.  Institutes support programs that benefit their membership.  Examples of programs include:  seminar series; topical workshops and conferences, including interaction with companies, political entities, or the media; visitor programs; educational forays such as interdisciplinary graduate programs, training grants, research experience for undergraduates or teachers, K12 outreach days; endowed postdoctoral fellowships; etc.  An Institute is meant to act as a a catalyst or enabling structure to bring together researchers with a common intellectual interest, to foment new and support existing collaborations, and to further research activity in that area.  At some universities, an Institute may have its own building or administer shared infrastructure.

A Center is usually a smaller, more focused group of researchers that is often expected to be financially self-supporting through multi-investigator external funding.  (Sometimes these are called Laboratories.)   Centers often exist within or are founded as the result of institutes.  A Center likely concentrates on a portfolio of specific research-related projects, rather than having broad programmatic efforts like an Institute.  The US NSF sponsors a number of center programs (MRSECs, ERCs, STCs, CCIs, and formerly NSECs), as does the US DOE (EFRCs).

An effective Center is almost self-defining:  It is able to accomplish focused research goals and to raise sufficient external resources to be self-supporting at least on the several year to decade timescale.  A good Center is able to identify and adapt to new research opportunities, while realizing which avenues are becoming played-out and should be set aside - basically, effective self-criticism while encouraging creativity through seed projects to generate new activity.   Longevity and research productivity metrics are two ways to assess the utility of a Center.

An effective Institute needs to serve its members by successfully supporting and carrying out its programs.  Because many Institutes have very broad programmatic goals, this requires serious "buy-in" - a decent fraction of the membership have to be willing to invest their time and energies to ensure that these programs are a success.  This only happens when the people involved really believe in the efforts and can see that they and the institution derive real benefit from the work.   This means that the Institute has to be responsive to the needs of its membership.   At the same time, the university has to assess (via research and funding metrics) the impact of the Institute and its programs, since the university has to decide whether the internal resources of the Institute could have been better spent elsewhere.

Both Institutes and Centers can be vulnerable to budgetary problems (internal and external, respectively) and to lack of engagement by membership.  At most places (the University of Chicago seems to be a big exception, since there Institutes have a lot of power) an Institute can be particularly exposed in tight times, since departments and much of their budgets are explicitly necessary for the reaching mission of the university, while Institutes are often viewed as elective or discretionary expenses.  In terms of engagement with members, like many organizations, Institutes and Centers succeed by succeeding and fail by failing.  You can't force people to collaborate, but once some do arise, productive collaborations lead to further productive collaborations.  Overall, Centers and Institutes appear to be key components of successful research universities.  It's not clear how these organizational structures (and their associated programs) will fare if we are in a long era of declining federal funding and internal cost cutting.

2d metallicity at low temperatures - a nice new result

To quote this blog from about 8.5 years ago (!): 

For years now, there has been a fairly heated debate about the nature of an apparent metal-insulator transition (as a function of carrier density) seen in various 2d electronic and hole systems. The basic observation, originally made in some Si MOSFETs of impressively high interface quality made in Russia, is that as the 2d carrier density is reduced, the temperature dependence of the sheet resistance changes qualitatively, from a metallic dependence (lower T = lower resistance) at high carrier concentration to an insulating dependence (lower T = higher resistance) at low concentration, with a separatrix in between with nearly T-independent resistance at some critical carrier density. A famous 1979 paper by the "Gang of Four" (Anderson, Abrahams, Licciardello, and Ramakrishnan) on the scaling theory of localization had previously argued that 2d systems of noninteracting carriers all become insulating at T=0 for arbitrarily weak disorder.

So, there has been a long-simmering controversy about why some 2d systems (electrons or holes) seem to show a really metallic temperature dependence of their conductance at low temperatures.  This dependence, where the conductivity apparently increases by, say, a factor of 2 from \(T =\) 4.2K down to 0.1 K, takes place over a temperature range where the scattering of electrons by lattice vibrations (the mechanism responsible for the increase in conductivity of ordinary metals as they are cooled from room temperature down to cryogenic temperatures) is supposed to be all finished.   I mentioned this as an ongoing controversy in '06 and again in '12.  What is going on here?

There is a new preprint from Bruce Kane and colleagues at Maryland that clarifies things considerably, in my view.  Kane, probably best known for proposing a quantum computing scheme involving individual phosphorus donors in Si, is a very clever experimentalist.  He has developed a method of creating field-effect transistors,where the conducting channel is the hydrogen-terminated surface of a Si wafer, and the gate dielectric is vacuum (!).  Using these devices, his group has been able to look at the apparent metallicity in both electrons and holes in the same system.  They find that the improvement in conduction at low temperatures has to do with the screening of charged impurities by the conducting system (and for the experts:  in Si the electrons are able to do this better than the holes because there are 6 conduction band valleys, while there is no valley degeneracy for the holes).  This doesn't directly get to the "fundamental" question about whether the true, zero-temperature ground state is insulating in a real, interacting system, but it does go a long way toward demonstrating why the conductivity still has a metallic change with temperature even though phonons should be out of the picture.

Updated: Advice on choosing a grad school

Over the last week I've run into a couple of readers of this blog who pointed out that many people never find older posts (unless they happen to use google with just the right search terms), and that it might be valuable to re-run updated versions of some of those, particularly the ones geared toward career advice.  This makes lots of sense, given how long this blog has been running and how readership has evolved.  So, here is the first of these updated re-runs (from 2011):  Advice on choosing a grad school. 

This is written on the assumption that you have decided, after careful consideration, that you want to get an advanced degree (in physics, though much of this applies to any other science or engineering discipline).  This might mean that you are thinking about going into academia, or it might mean that you realize such a degree will help prepare you for a higher paying technical job outside academia.  Either way,  I'm not trying to argue the merits of a graduate degree.

• It's ok at the applicant stage not to know exactly what you want to do.  While some prospective grad students are completely sure of their interests, that's more the exception than the rule.
• If you get the opportunity to visit a school, you should go.  A visit gives you a chance to see a place, get a subconscious sense of the environment (a "gut" reaction), and most importantly, an opportunity to talk to current graduate students.  Always talk to current graduate students if you get the chance - they're the ones who really know the score.  A professor should always be able to make their work sound interesting, but grad students can tell you what a place is really like.
• I know that picking an advisor and thesis area are major decisions, but it's important to realize that those decisions do not define you for the whole rest of your career.  I would guess (and if someone had real numbers on this, please post a comment) that the very large majority of science and engineering PhDs end up spending most of their careers working on topics and problems distinct from their theses.  Your eventual employer is most likely going to be paying for your ability to think critically, structure big problems into manageable smaller ones, and knowing how to do research, rather than the particular detailed technical knowledge from your doctoral thesis.  A personal anecdote:  I did my graduate work on the ultralow temperature properties of amorphous insulators.  I no longer work at ultralow temperatures, and I don't study glasses either; nonetheless, I learned a huge amount in grad school about the process of research that I apply all the time.
• Always go someplace where there is more than one faculty member with whom you might want to work.  Even if you are 100% certain that you want to work with Prof. Smith, and that the feeling is mutual, you never know what could happen, in terms of money, circumstances, etc.  Moreover, in grad school you will learn a lot from your fellow students and other faculty.  An institution with many interesting things happening will be a more stimulating intellectual environment, and that's not a small issue.
• You should not go to grad school because you're not sure what else to do with yourself.  You should not go into research if you will only be satisfied by a Nobel Prize.  In both of those cases, you are likely to be unhappy during grad school.  
• I know grad student stipends are low, believe me.  However, it's a bad idea to make a grad school decision based on a financial difference of a few hundred or a thousand dollars a year.  Different places have vastly different costs of living - look into this.  Stanford's stipends are profoundly affected by the cost of housing near Palo Alto and are not an expression of generosity.  Pick a place for the right reasons.
• Likewise, while everyone wants a pleasant environment, picking a grad school largely based on the weather is silly.
• Pursue external fellowships if given the opportunity.  It's always nice to have your own money and not be tied strongly to the funding constraints of the faculty, if possible.  (It's been brought to my attention that at some public institutions the kind of health insurance you get can be complicated by such fellowships.  In general, I still think fellowships are very good if you can get them.)
• Be mindful of how departments and programs are run.  Is the program well organized?  What is a reasonable timetable for progress?  How are advisors selected, and when does that happen?  Who sets the stipends?  What are TA duties and expectations like?  Are there qualifying exams?  Where have graduates of that department gone after the degree?  Know what you're getting into!
• It's fine to try to communicate with professors at all stages of the process.  We'd much rather have you ask questions than the alternative.  If you don't get a quick response to an email, it's almost certainly due to busy-ness, and not a deeply meaningful decision by the faculty member.  For a sense of perspective:  I was traveling yesterday, and during that time my email queue expanded by about 50 messages, not counting all the obvious spam I deleted. 

There is no question that far more information is now available to would-be graduate students than at any time in the past.  Use it!  Look at departmental web pages, look at individual faculty member web pages.  Make an informed decision.  Good luck!

What are liquid crystals?

Once you accept the idea that the simple, microscopic interactions between bits of matter can lead to the emergence of dramatic collective properties when large numbers of particles are concerned, it's not surprising to realize that there are many different ways that large ensembles of particles end up organizing.  As mentioned previously, a true liquid is a system where the average distance between the particles is comparable to the particle size, but the particles are in constant motion and there is no particular long-range order to the way the particles are arranged.

New possibilities present themselves if the particles have some kind of "internal degree of freedom".  For example, think of the particles not as little featureless billiard balls, but as elongated objects.  Now we can consider having the orientation of all the particles have some long-range correlation.  A liquid crystal is an emergent phase when the particles are close together and there is not 3d spatial order in the arrangement of particle positions, but there is order in the orientations of the particles.  In nematic liquid crystals, the centers of mass of the particles are completely spatially disordered, but there is long-range order in their orientation. For example, they could all be pointing the same direction, indicated by the not-so-cleverly-named vector, the director.  Cholesteric liquid crystals have some twist or chirality to the particle orientation.  In smectic liquid crystals, the particle centers of mass are actually spatially ordered in one direction, but not in the other two (i.e., you can think of stacks of layers of particles, with particles free to move within each layer).  The wiki page about liquid crystals gets into the history of these systems, and here is a nice webpage that classifies them.  Liquid crystals are very useful because their directed nature gives them anisotropic optical properties, and if the objects in question are polar molecules, it is possible to reorient them electrically.  This combination enables many technologies, almost certainly including the display device you're using to read this.

There was a time when I was somehow skeptical that all these phases were "real" thermodynamic phases.  I was used to solids, liquids, and gases, and I'd learned about "hard" condensed matter phases like ferromagnets and superconductors that dealt with emergent properties of the electron gas.  Somehow these liquid crystal things didn't seem like the same sort of thing to me.  Then I read the really great book by Chaikin and Lubensky, and saw things like the figure at right (from G. S. Iannacchione and D. Finotello, Phys. Rev. E 50, 4780 (1994)).  The figure shows the specific heat of a liquid crystal (in some nanopores) as it goes through a thermally driven transition between the nematic and isotropic phases, as a function of scaled temperature, \(t \equiv (T/T_{\mathrm{c}})-1\).  This kind of sharp, divergent feature and scaling as a function of temperature are hallmarks that show these phases and their transitions are every bit as real as any other thermodynamic phase, even though the materials are squishy.

Java applets for physics - a great resource being strangled by security?

As many of my readers know, starting in the late '90s, many clever, creative people around the world wrote cute (and sometimes very sophisticated) Java applets to demonstrate certain physics and engineering concepts.  Examples include this great site by the University of Buffalo, a virtual lab by the University of Oregon, this resource by UCLA, this outstanding site from the University of Barcelona, etc.  Many of us owe a real debt of gratitude for these resources, as they have been great educational tools. 

A problem has arisen, however.  You will notice that none of the applets linked above actually run.  Because of security concerns about Java, the latest versions of Java require applets to have been compiled, authenticated, and certified (via electronic security certificates), or the applets simply won't be run by the virtual machine.   For actively maintained sites (such as the excellent "physlet" effort from Davidson), the authors and maintainers have thoughtfully recompiled and updated their code.  Others (the University of Colorado) have rewritten everything (!) in Flash or HTML5.  Unfortunately, these are the exceptions, and many other cool sites are orphaned, with clever code that can't be run.

If anyone knows a work-around (some kind of emulator that would run the code in a walled-off way?), please describe it in the comments.  It would be a real shame if the accumulated excellence of all those older sites was wiped out.  Thanks.

Several items, including interesting reading

• Celebrity scientist Lawrence Krauss has written an article (pdf) about whether celebrity scientists are good for society, and noting that celebrity \(\ne\) greatest scientific researcher, necessarily.  In response to the title ("Celebrity scientists:  Bad for science or good for society?") it's tempting to be snarky and respond "Why not both?". Note that this guy is conspicuously absent from the article.
• Hat tip to the Angry Physicist for pointing out this article about the US military academies.  I found it genuinely shocking.  I'd always had the impression growing up, based on anecdotes I guess, that West Point and Annapolis in particular were incredibly selective and could be very academically demanding.  The academy graduates I've met over the years had only reinforced this idea by being very impressive people.  I was very dismayed to read about the apparently low academic standards.
• I was dismayed by two NSF-related issues in the last week.  First, NSF has gotten increasingly rigid about enforcing minutia of their guidelines over the last couple of years.  This is particularly frustrating when combined with guidelines that are themselves ambiguous (e.g., saying that a preproposal must include certain items, but not saying whether other items like collaboration letters are desired, or worse, forbidden because adding extra material can be grounds for getting bounced without review), and then being hard to reach for clarification.  This is a further sign that they are understaffed and overwhelmed.
• Second, in the Major Research Instrumentation call, NSF no longer allows grant funds to pay for technical staff.  That means that an approach that had previously been extremely helpful (have NSF pay for 75% of a staff person the first year, 50% the second, and 25% the third, so that a university can taper in technical staff support over time) is no longer possible. 
•  An old friend of mine does an excellent podcast, and he spent some time talking with me - it was really fun.

What is a phase (of matter)?

Defining "a phase of matter" for a popular audience is a tricky business, with choices ranging from the overly simplistic and therefore vacuous (a collection of matter that has homogeneous, uniform, well-defined physical properties that are distinct from other such phases), to the very technical, to sophistry (like the famous definition of obscenity).

A critical ingredient missing from the simple definition above is the deep, profound point that phases of matter only make sense as emergent from the collective behavior of many constituents (the dynamics of which are often governed by simple rules).  A single water molecule is not a solid, a liquid, or a gas - it is just a single molecule, with a structure and some mechanical, electronic, and optical properties that can be calculated with pretty good accuracy through "ab initio" techniques like density functional theory and its relatives.  (Note:  Even doing that is bloody hard, given that ten electrons is actually a lot from the standpoint of quantum chemistry.)

However, if you take a collection of \(N\) water molecules and stick them in a box of a fixed volume \(V\), with a certain amount of kinetic energy \(E\), and let them bounce around and do their thing, interacting with each other via van der Waals and longer-ranged (dipolar, since water is a polar molecule) forces, something interesting will happen.  To avoid difficult conceptual issues about reversibility, let's imagine you have a whole bunch of boxes like this, all prepared with the same \(N, V\) and \(E\) but with the microscopic initial conditions like molecular positions and velocities scrambled.  (This is the "microcanonical ensemble", for experts.)  Wait an unspecified long while. What you will find is that as \(N\) increases from 1 to a large number, at some point you will start being able to classify the emergent, "coarse-grained" properties of these boxes.  For a sufficiently low \(E\), you will find that the vast majority of the boxes contain a blob of water molecules that have arranged themselves in a spatially ordered way, with spatially periodic positions and orientations.  There will be a few leftover molecules bouncing around, and the blob will have a certain amount of jiggling going on.  If you shook the box, you would see that the blob moves rigidly, exhibiting some resistance to deformation, though the molecules at the edges would move more easily, and would be constantly exchanging with the few leftover molecules bouncing around the rest of the box.  Somehow, the molecules in those boxes have spontaneously broken a bunch of symmetries (picking out spatial locations that exhibit some periodicity and rotational symmetry), and what we think of as "bulk" properties have emerged, like density, some kind of elastic modulus, a speed of sound, etc.  There is now some interface as well, between the solid and the mostly unoccupied void. 

For higher \(E\), you will probably find that the vast majority of boxes contain a blob of water molecules that are very close together, bumping into each other all the time, but tumbling around with no particular relative orientation.  This blob of water has an interface with the remaining "gas", and does not respond rigidly if it bumps into a wall of the box.  If you could look at all the molecules, you could add up how much energy it takes to expand the surface of that blob - this is proportional to the surface tension.

At still higher \(E\), you will find that the water molecules are roughly homogeneously distributed throughout each box, bumping into each other and the walls.  You could still think about an average density for this gas, and if you banged on the wall of the box to impart momentum to the molecules that happen to be hitting that wall, you could watch the propagation of a density wave (sound!) through the molecules.   In the really high \(E\) limit, the molecules decompose and the constituent atoms ionize - this is a plasma.

Each of these arrangements that you would find in a very large percentage of such imaginary boxes, with its emergence of well-defined "bulk" physical properties (including more subtle ones I haven't mentioned, like magnetic order or electrical conductivity) as \(N\) grows to a statistically large value, is a thermodynamic phase of matter.    Why are these the particular ones that occur?  Why do water molecules tend to form particular solid structures?  Why don't we see the spontaneous appearance of phases that look very different, like long 1-d chains of water molecules, for instance?  It's not at all obvious!  That's the fun of condensed matter physics:  The answer somehow lies in the microscopic properties of the molecules and their interactions - it's latent in there as soon as you have one molecule, but somehow cannot emerge and be realized except through the collective response of a large ensemble.  More soon.

More posting soon.

Sorry for the brief hiatus.  Many urgent tasks (e.g., proposal deadlines, prep for semester, grad admissions).  Suggestions for forthcoming topics are always appreciated.  Coming up in future installments:  "When does water become wet?", "What is a phase?", "What are liquid crystals?", and "Centers, Institutes, and all that".

Great elasticity demonstration

I've linked to Dustin Sandlin before.  He does a fantastic series of YouTube videos that are readily accessible by a lay audience and show why science is fun.  Here is his look, using ultrahighspeed video, at why dry spaghetti tends to break in at least three pieces when flexed from the ends.  As he says, this is something that Feynman himself couldn't readily unravel.  Watch the video before you scroll down and read my spoiler description of the mechanism.

...

...

This video shows some great elasticity concepts that we generally don't teach in the undergrad physics curriculum.  Flexing the noodle puts the top in tension and the bottom in compression - if you assume simple elasticity (e.g., stress = (Young's modulus)(strain)), and you consider the resulting forces and torques on a little segment of the noodle, you can calculate the shape (e.g., vertical deflection and tilt angle as a function of position along the noodle) of the bent spaghetti, though you have to assume certain boundary conditions (what happens to the displacement and tilt at the ends).  As the flexing is increased, at some point along its length (more on this in a minute) the noodle fractures, because the local strain has exceeded the material strength of the pasta.  One way to think about this is that the boundary condition on one end of each piece of the noodle has now changed abruptly.  Each piece of noodle now starts changing shape, since the previous strained configuration isn't statically stable anymore.  That shape change, the elastic information that the boundary condition has changed, propagates away from the fracture point at the speed of transverse sound in spaghetti (probably a couple of km/s).  The result is a propagating kink in the noodle, the severity of the kink depending on the local curvature of the pre-fracture shape.  If that local strain again exceeds the critical threshold, the noodle will fracture again.  The fact that we need really high speed photography to see the order of breaking shouldn't be that surprising - the time interval between fractures should be the size of the noodle fragment (around 3 cm) divided by the speed of sound in the pasta (say 2000 m/s), or around 15 microseconds!  (If I was really serious, I'd go the other way and use the video record of the propagating kink to measure the speed of transverse sound in pasta.)

This problem is actually somewhat related to another mechanics question: why do falling chimneys tend to break into three pieces?  Again, treating the chimney as some kind of elastic beam clamped at the bottom but free at the top, one can find the (quasi static, because the time it takes sound to propagate in the chimney material is much shorter than the time for the chimney to fall) shape of the flexing chimney.  There are two local maxima in the strain, and that's where the chimney tends to break.  Note that the chimney case is quasi static, while the spaghetti case really involves the dynamics of the flexing noodle after fracture. 

The bottom line:  I want one of those cameras.

Lack of self-awareness, thy name is John Horgan.

I see that Scientific American is reorganizing its blogging efforts.  I hope it works out well for them.  Call me if you want someone to blog about condensed matter and nanoscale science.  I'd really enjoy talking to a wider audience and would, of course, tailor my style accordingly.

When looking at their site, though, I came upon this piece by John Horgan, about whom I have written previously.  This latest essay is meant to be advice for young science writers.  Because he is a smart person with great experience in science journalism, his basic advice does have some kernels of merit (be skeptical of claims of scientists; pay attention to who is talking about science and their possible agendas).  His other points strike me as odd or beside the point to varying degrees.  (e.g., scientists are people and therefore have a human context to their work, but claiming that the majority of US science is shaped by capitalism and militarism is just nutty; inequality, our screwed up healthcare system, and militarism are all distressing, but what does that have to do with talking about a large part of science?)

The very first point that Horgan makes got my attention, though, and nearly broke my irony-meter.  He writes (his emphasis): "Most scientific claims are bogus. Researchers competing for grants, fame, glory and tenure often—indeed usually–make exaggerated or false claims, which scientific journals and other media vying for readers eagerly disseminate."  While I recognize that there have been claims to this effect in recent years, I think it is pretty hilarious that Horgan can warn about this with a straight face.  This is the guy who vaulted onto the larger, international stage by writing a book called The End of Science back in 1996.  Yeah, that wasn't at all an exaggerated or false claim made with the intent of capturing as much media attention as possible.  Nope.

Long odds: Proposals and how we spend our time

We just completed the two-day kickoff symposium of the Rice Center for Quantum Materials.  It was a good meeting, and the concluding panel discussion ended up spending a fair bit of time talking about the public policy challenges facing basic research funding in the US (with some discussion of industry, but largely talking about government support).  Neal Lane is an impressive resource, and lately he and Norm Augustine have been making the rounds in Washington trying to persuade people that it's a dire mistake to let basic research support continue to languish for the foreseeable future.

Over the December/January timeframe, I'm spending time on several grant proposals.  Three of them have a priori odds of success (based on past years, dividing awards by the number of initial proposals) less than 5%.  Now, obviously longshots have their place - you can't win if you don't play, and there is no question that thinking, planning, and writing about your ideas has utility even if you don't end up getting that particular award.  Still, it seems like more and more programs are trending in this awful positive feedback direction (low percentage chance per program = have to write more grants = larger applicant pool = lower percentage chance).  Many of these are prestigious center and group programs that are greatly desired by universities as badges of success and sources of indirect costs, and by investigators as sources of longer term/not-single-investigator support.  When yields drift below 5%, it really does raise questions:  How should we be spending our time, one resource that we can never replenish?  Does this funding approach make sense?  When the number of potentially "conflicted" people (e.g., coauthors/collaborators over the last four years for every person affiliated with a big center grant) exceeds 1000 (!), who the heck is left to review these things that has any real expertise?

Science and sensationalism: The allure of superlatives and bogus metrics

I helped out a colleague of mine today, who was fact-checking a couple of sentences in a story that's going to come out in a large circulation magazine (that shall remain nameless).  The article is about graphene, and in draft form included a sentence along the lines of "Graphene is 1000x better at conducting electricity than copper."  That sounds great and exciting.  It's short, simple, and easy to remember.  Unfortunately, it's just not true unless accompanied by a huge asterisk that links to a page full of qualifications and disclaimers. 

The challenge:  Come up with a replacement that gets the main point across (graphene is a remarkable material) without being a gross distortion or dissolving into scientific jargon. 

My response:  "Graphene is an electrical conductor that rivals copper and silver, and is much lighter and stronger."  At least this is true (or moreso, anyway), though it's longer and doesn't have an easy-to-remember number in it. 

The search for a simple, one-sentence, exclamatory pronouncement can lead science journalists (and university public relations people) down a dangerous path.  Often really great science is simply more complicated than a sound-bite.  Moreover, the complications can be fascinating and important.  It takes a special journalist to recognize this.

Interesting superconductivity developments

Three superconductivity-related things during the crazy end-of-semester time crunch. 

First, the paper that I'd mentioned here has been accepted and published in Nature Materials here.  That one reports signatures of superconductivity in a single atomic layer of FeSe on SrTiO₃ at around 100 K.  This result is not without controversy, as it's very hard to do standard transport in single layers of material like this in UHV, and usually people want to have multiple signatures besides resistivity when claiming superconductivity.

In that vein, there is a recent preprint that reports superconductivity above 190 K (!) in H₂S under high pressure.  The belief by the authors is that this is conventional superconductivity, related to classic work over many years (see here and here for example) by Neil Ashcroft and others discussing superconductivity in metallic hydrogen (possibly responsible for things like Jupiter's large magnetic field, for instance).  Because of the challenges of doing ultrahigh pressure measurements in diamond anvil cells, this, too, has only resistivity apparently dropping to zero as its main evidence for superconductivity.  It looks pretty cool, and it will be interesting to see where this goes from here.

Lastly, in Nature there is a paper that looks at trying to understand recent measurements of copper oxide superconductors when hit with ultrafast laser pulses.  The argument in those pump-probe experiments is that smacking the cuprates while in the normal state is enough to produce apparent transient superconductivity (as inferred on picosecond timescales with another optical pulse used to measure a quantity related to the conductivity).  The new paper claims that the initial pulse produces lattice distortions that should favor higher temperature superconductivity.

The common thread here:  There continue to be tantalizing hints of possible higher temperature superconductors, but in all of these cases it's really darn hard to do the measurements (or at least to bring multiple tools to bear).  For a nice look at this topic, see these recent words of wisdom.

Writing style, "grand visions", and impact

It's hard for me to believe that over eight years (!) have passed since I wrote this.  Recently I've been thinking about this again.  When writing proposals, it's clearly important to articulate a Big Picture vision - why are you working on a problem, where does that problem fit in the scheme of things, and what would the consequences be if you achieved your goals?  Some people's writing styles tilt more in this direction (e.g., our team is smart and highly accomplished, and we have a grand vision of a world set free by room temperature superconductors - this path will lead us there) and others lean more toward the concrete (e.g., our team is smart and highly accomplished, and we've thought carefully about an important problem - here is what we are going to do in some detail, what the challenges are, and what it will mean).  I tend to lean toward the latter.  It's not that I lack a grand vision - I'd just rather underpromise and overperform.  Still, it's clear that this doesn't always pay dividends.  (Of course, the best of all possible worlds is to promise a grand vision and actually achieve it, but that's extremely rare.)

Beautiful mechanical design, + excellent outreach

Yesterday I came across this video series, put up by "EngineerGuy" Bill Hammack.   It shows a mechanical analog computer originally designed by Michelson for building up Fourier series (sums of sinusoids) of up to twenty integer multiples of a fundamental frequency.   Moreover, you could use this machine to go backwards, and mechanically do Fourier decomposition of periodic waveforms.  It's really wonderful.  I would love to have one to use as a teaching tool, and I'm sure some enterprising person will figure out how to 3d print all the relevant parts (except the springs and cables), or perhaps build one out of Lego. 

I also wanted to point out Hammack's other videos.  This is great outreach - really accessible, clear, well-produced content.

Chapter epigraphs from my book

Because of the vagaries of British copyright law and their lack of the concept of "fair use", I am not allowed to use clever little quotes to start the chapters of my nano textbook unless I have explicit permission from the person or their estate.  Rather than chasing those, I've sacrificed the quotes (with one exception, which I won't reveal here - you'll have to buy the book).  However, on my blog I'm free to display these quotes, so here they are.

• "I would like to describe a field, in which little has been done, but in which an enormous amount can be done in principle. This field is not quite the same as the others in that it will not tell us much of fundamental physics (in the sense of, “What are the strange particles?”) but it is more like solid-state physics in the sense that it might tell us much of great interest about the strange phenomena that occur in complex situations. Furthermore, a point that is most important is that it would have an enormous number of technical applications. What I want to talk about is the problem of manipulating and controlling things on a small scale."  - Richard Feynman, "There's Plenty of Room at the Bottom" lecture, Engineering and Science 23, 22 (1960)
• "More is different." - Phil Anderson, Science 177, 393 (1972).
• "Solid state I don’t like, even though I started it." - Wolfgang Pauli, from AIP's oral history project
• "How do we write small? ... We have no standard technique to do this now, but let me argue that it’s not as difficult as it first appears to be." - Richard Feynman, "There's Plenty of Room at the Bottom" lecture, Engineering and Science 23, 22 (1960)
• "God made solids, but surfaces were the work of the devil." - Wolfgang Pauli,  quoted in Growth, Dissolution, and Pattern Formation in Geosystems (1999) by Bjørn Jamtveit and Paul Meakin, p. 291.
• "The importance of the infinitely little is incalculable." - Dr. Joseph Bell, 1892 introduction to Arthur Conan Doyle's A Study in Scarlet
• "Magnetism, as you recall from physics class, is a powerful force that causes certain items to be attracted to refrigerators." - Dave Barry, 1997
• "If I were creating the world I wouldn’t mess about with butterflies and daffodils. I would have started with lasers, eight o’clock, Day One!" - Evil, Time Bandits
• "Make big money!  Be a Quantum Mechanic!" - Tom Weller, Science Made Stupid (1985). 
• "I am an old man now, and when I die and go to Heaven there are two matters on which I hope for enlightement. One is quantum electrodynamics and the other is the turbulent motion of fluids. And about the former I am rather more optimistic." - Horace Lamb, 1932 address to the British Association for the Advancement of Science, as cited in Eames, I., and J. B. Flor. "New developments in understanding interfacial processes in turbulent flows." Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences 369.1937 (2011): 702-705
• "Almost all aspects of life are engineered at the molecular level, and without understanding molecules we can only have a very sketchy understanding of life itself." - Francis Crick, What Mad Pursuit: A Personal View of Scientific Discovery (1988), p. 61
• "Be a scientist, save the world!" - Rick Smalley 

Refereeing redux.

I was also asked:

"I would like to see a post addressing how to handle a paper sent back by the editor for another round of reviews. Of particular interest to me: what do you do if you notice errors that escaped notice (or weren't present) in the original manuscript? What if the authors answered your issues well in the response letter, but didn't include those modifications in the manuscript? What advice would you have if the authors have clearly done the experiments and theory well, and the results are worth publishing, but the writing/figures are still not at a publishable level following their revisions?"

My answers are probably what you'd guess.  I try hard to identify possible errors the first time through refereeing a paper.  If I spot something on the second round that I'd missed, I try to be clear about this by writing something like "Also, on this pass through the paper, I had the realization that [blah blah] - my apologies for not catching this on the first round, but I think it's important that this issue be addressed."  Again, I try hard not to miss things on the first pass, since I know how annoying it is from the author side to be hit with apparently new objections that could have been addressed in the first revisions.

I've definitely had cases where the authors wrote a great response and then made almost no changes to the manuscript.  In this situation, I usually say, "The response letter was very convincing/clarifying regarding these points, and I think it is important that these issues are discussed in the manuscript itself."  I would then, in the "comments to the editor" part of the report, re-emphasize this, in the hopes that the editor will push the authors about it.

If the manuscript contains good science but is written at an unpublishable level (rare, but not unheard of), I try to point this out diplomatically (e.g., "The science here is very interesting and deserving of publication, but I strongly recommend that the presentation be revamped substantially.  I think swapping the order of the figures would make the story much clearer.").  Again, to the editors, I might make more specific recommendations (e.g., "This manuscript absolutely needs to be closely edited by a native speaker of English" if it's full of truly poor grammar).

The basic strategy I follow is to try to evaluate the science and offer as useful and constructive feedback as possible (given that I can't spend tons of time on each refereeing assignment), in the kind of professional and courteous tone I'd like to read in reports on my own work.

"What happened to PRL?"

A commenter wrote the following:  "About PRL, I do have a concrete question. You've been around for some time, I am new in the business. Can you explain what happened to it? Twenty years ago it used to be the journal to publish in, now it is an afterthought."

Physical Review Letters remains a premier place to publish high impact physics results in letter-format (that is, typically 4-ish page papers with around 4 figures).   I think that the recently arrived editor in chief Pierre Meystre is working hard to revitalize PRL as a "destination journal" for physics results, where you know that the primary audience comprises physicists. 

That being said, the origins of some of PRL's (possible) loss of cachet are immediately obvious.  Twenty years ago, Nature and Science were not as highly regarded within the physics community as places to publish.  Nature Publishing Group did not have all of its various progeny (Nature Physics, Nature Materials, Nature Nanotechnology, Nature Photonics being the four most relevant here).  Likewise, the American Chemical Society's journal offerings used to be a lot less friendly to physicists.  Now there are Nano Lett., ACS Nano, ACS Photonics, ACS Applied Materials and Interfaces.   It's a far more competitive journal marketplace, and the Phys Rev journals have been slow to innovate.  Furthermore, I think there is a broad perception that PRL's refereeing can be long, arduous, contentious, and distressingly random.  Some of the competing journals somehow are able to be rapid and on-target in terms of the expertise of the referees.  If you have a hot result, and you think that refereeing at PRL is highly likely to take a long time and require a protracted fight with referees, other alternatives have room to make inroads. 

Somehow PRL needs to improve its reviewing reputation in terms of accuracy and timeliness.   That, I think, would be the best way to be more competitive.  That, and a re-design of their webpage redesign, which is neither particularly attractive or functional.

What are skyrmions?

Skyrmions are described somewhat impenetrably here on wikipedia, and they are rather difficult beasts to summarize briefly, but I'll give it a go.  There are a number of physical systems with internal degrees of freedom that can be described mathematically by some kind of vector field.  For example, in a magnetically ordered system, this could be the local magnetization, and we can imagine assigning a little vector \( \mathbf{m}\) (that you can think of as a little arrow that points in some direction) at every point in the system.  The local orientation of the vector \( \mathbf{m} \) depends on position \(\mathbf{r}\), and there is some energy cost for having the orientation of \( \mathbf{m} \) vary between neighboring locations.   In this scenario, the lowest energy situation would be to have the direction of \(\mathbf{m}\) be uniform in space.

Now, there are some configurations of \( \mathbf{m}(\mathbf{r})\) that would be energetically extremely expensive, such as having \( \mathbf{m}\) at one point be oppositely directed to that at the neighboring sites.  Relatively low energy configurations can be found by spreading out the changes in \(\mathbf{m}\) so that they are gradual with position.  Some of these are topologically equivalent to each other, but some configurations of \(\mathbf{m}\) are really topologically distinct, like a vortex pattern.  Examples of these topological excitations are shown here.   With a lone vortex, you can't trivially deform the local orientations to get rid of the vortex.  However, if you combine a vortex with an antivortex, it is possible to annihilate both.

Skyrmions (in ferromagnetis) are one kind of topological excitation of a system like this.  They are topologically nontrivial "spin textures", and in real magnetic systems they can be detected through techniques such as magnetic resonance.   It's worth noting that there are other topological defects that are possible (domain walls that can be soliton-like; defects called "cosmic strings" if they are defects in the structure of spacetime, or "line defects" if they are in nematic liquid crystals; monopoles (all arrows pointing outward from a central point) sometimes called "hedgehogs"; and other textures like the boojum (a monopole pinned to the surface of a system; relevant in liquid crystals and in superfluid ³He)).  With regard to the last of these, I highly recommend reading this article, which further cemented David Mermin as a physics and science communication idol of mine.