A cool result

There's a new asap paper in Nano Letters that is very slick. There has been a lot of interest in the last few years in plasmonics - the controlled manipulation of plasmons, collective oscillations of the electronic fluid in metals. Plasmons are pretty remarkable excitations. Because they involve displacement of the electron density, they necessarily result in local electric fields near metal surfaces (useful for optical antenna sorts of effects), and they can (under the right circumstances) couple efficiently to electromagnetic radiation. Plasmon response to light can be very pronounced, ranging from resonant scattering or absorption (for example, why certain types of glass are colored) to more complex dispersive effects, including negative (effective) indices of refraction. Plasmons are also responsible for helping light to transmit through sub-wavelength apertures. However, as far as I know, until now none of these effects have depended in any significant way on the angular momentum of light. In this new result, researchers from the Technion in Israel have designed aperture structures that can couple selectively to left- or right-circularly polarized light. The trick is in finding a situation such that the angular momentum of the light (essentially the spin of the photons) couples selectively to plasmon modes in the apertures that have matching orbital angular momentum. I don't fully understand how the two experiments described in the paper work, but it's a neat, clever result.

Four items

Four items, and a physics post later in the week.

• Is "just-in-time" supply chain management truly the work of the devil, or merely incredibly annoying? We've had a problem with a gate valve on a piece of cleanroom equipment at my institution, and the vendor (a) has no spare valves; (b) has no spare parts for the valves; and (c) says it'll take around 4 weeks to fab a replacement valve. Now, I understand why a business wouldn't want a huge inventory sitting on shelves, and that there are real fixed costs associated with inventories. Still, how hard would it be to have some spare parts, particularly when these things don't go bad when stored? I can tell you that it doesn't make me predisposed to ever buy anything from this supplier again. So, while it may be penny-wise, it sure feels pound-foolish for companies to alienate customers by having no backup supplies at all.
• Ahh, scientific publishing. Two folks from Cornell used an amusing computer program to generate a grammatically correct but completely nonsensical fake paper (pdf). They then got that paper accepted to an open-access journal, without the knowledge of the editor (!), with the strong implication being that this publisher was willing to publish literally anything as long as the authors are willing to pay the fees. Wonderful. I've suspected for a while (basically when a couple of publishers spammed me about being a contributing editor on journals I'd never heard of, back when I was a brand new assistant prof) that there are some shady practices out there.
• Also regarding scientific publishing, I was shocked and appalled (ok, not really, but certainly surprised) when I got the proofs of an article that we have coming out in Phys Rev B. Why? Because it was clear from the marked-up "author query" version of the manuscript that the AIP production office had converted our beautiful LaTeX manuscript into Microsoft Word format for editing. What is the world coming to?!
• Lastly, I was fortunate enough to receive a new iPod Touch as a gift. Anyone out there have suggestions for must-have apps?
  

The revolution will be twittered.

Not a physics post, but an observation. There is a major event going on in Iran right now - protests involving many thousands of people; rioting; the most political upheaval since the 1979 revolution. I hope that everything works out for the best - any country with a Supreme Leader needs a new governance structure, IMO. Anyway, twitter is being used as a major tool by the Iranian protesters. So much for my general perception that twitter was only for people more self-indulgent than bloggers (ahem.). It's fascinating and alarming to watch events unfold from halfway around the world, while CNN reports on things like Sarah Palin/David Letterman feuds. It's as though the "news" network has forgotten what real news is....

Nanoscale, the book

No, I have not compiled my blog postings into dead-tree format. Nor have I finished my textbook based on my graduate nanoscale physics course sequence. Instead, I wanted to point out this book, which is a cute volume with lots of computer-rendered pictures of crystal structures and the like. It's an admirable attempt to give the reader a sense of the atomic-scale composition of materials, along with brief, informative, often fun descriptions. While there are a few minor typos that seem to be caused by autocorrection run amok, the book remains entertaining and educational, with very well crafted illustrations. The book has its own website, too.

This week in cond-mat

Two papers appeared on the arxiv in the last couple of days concerning the very hot topic of quantum-limited measurement. I'm no expert in the area, but here's a quick summary of the idea.... Anyone who's read anything about quantum mechanics is familiar with the popular "gamma-ray microscope" thought experiment meant to highlight the Heisenberg uncertainty relation. In lay terms, trying to use light to determine the location of a particle with arbitrarily high precision requires, in a simple thought experiment, light of a correspondingly short wavelength. Shorter wavelength = higher energy photons = higher momentum photons = big momentum transfer to the particle. Thus, the more precisely you localize the particle, the less you know about its momentum. This is an adequate handwave for the popular press, but the real situation can be more subtle. Still, in the general problem of quantum measurement, one is often concerned about "back action" - the fact that coupling your system to a detector (thus enabling you to make some kind of measurement of an observable) generally perturbs the equations of motion of the system itself. It turns out, under certain very special circumstances, it is possible to design a measurement and pick observables such that the effect of back action is essentially confined to some variable that you don't care about. The net result in that case is that you can measure your particular observable to higher precision than a simplified uncertainty argument would suggest is possible.

Two groups, those of Keith Schwab at Cal Tech (paper here) and Konrad Lehnert at Boulder/JILA (paper here), have managed to do this type of measurement, looking at the position of a nanoscale mechanical resonator. In both cases, they are able to couple the resonator to a microwave LC resonator in such a way that they can measure the mechanical displacement better than the standard quantum limit. These measurements are very technologically impressive, and they open up the path toward really exciting possibilities, including entanglement of different nanomechanical systems, clever cooling schemes, and true quantum mechanics measurements.

Random tidbits

Several minor things....

• I've got an article on single-molecule electronics coming out in the June issue of Physics World. It's reasonably accessible, and I'm pretty happy with how it turned out, though I wish there had been more space to discuss the theoretical challenges.
• This is damned cool. I had an undergrad course that was like the baby version of this - building up transistors into logic gates; then using logic gates to build a shift register; then building and programming a little 6502-based computer to run a model train network. This guy's work puts all that to shame by comparison.
• The pseudonymous Kyle Finchsigmate, always entertaining and clever (often profane), has started a wiki site devoted to chemistry experimental techniques. In comments about that I came across this site from Rochester. I think it would be great to have a site like this about experimental physics, though clearly it would take a lot of work from many people to have it be any good....
• I've been asked by a reader to solicit discussion and opinions about the various journal online manuscript submission/review systems. Which ones are good, and which ones are lousy? From what I can tell, the APS system is decent (though it always seems to complain erroneously about mistakes in my references and article lengths), and the Paragon system from ACS is quite good. The Nature publishing group one also seems to be put together well. I'm not a fan of "Manuscript Central" or whatever it is that Elsevier and IEEE use. What do you all think?
• Thank goodness McLeroy was not confirmed as head of the TX board of education.
  
• This'll be the last update for about the next 9 days or so, since I'll be traveling with very limited 'net access.
  

Plastic Fantastic thoughts

Reading Eugenie Reich's Plastic Fantastic brought me right back to the heady days of my postdoc, job search, and nearly a year spent with a student chasing what turned out to be fabricated results. In hindsight I learned an awful lot about human nature and the sociology of science, and some of that is conveyed to readers of this book, though not all.

First, the book review. I think Reich writes well, and I think she did a good job simplifying the science where appropriate for a more general audience. Criticizing the details (e.g., I wasn't a big fan of her definition of "polaron") misses the larger point (you don't need to know what a polaron is to appreciate the fact that Schon didn't fully get what polarons are either). Personally I think it would have been useful to spend more time on standard scientific practice at Bell Labs - Schon's claims (going back to his doctoral work in Germany) that he didn't keep notebooks or save primary data aren't just damning - they're completely outside what I saw essentially everyone else do, both at Bell and in grad school. How on earth did this happen? How did no one immediately supervising Schon never notice that he had no notebooks?! The idea that researchers at Bell were so independent that no one would ever notice this is crazy. I also think it would have been good to spend a bit more time on the denoument, at least discussing further the major issues raised by this whole affair: what are the responsibilities of co-authors? What are the responsibilities of managers? There were also some nuances of what happened as the scandal broke that I didn't see (though I could've missed them on a quick read), including some choice remarks by Batlogg that were rather remarkable at the time. [One other point: Reich points out that the Departments of Defense and Energy don't have central offices of research integrity. Strictly speaking, that's right, but the way it's written makes it sound like DOD and DOE never even consider the matter, which is not true. Since 2000, anyway, DOE has used the following (pdf) policy regarding research misconduct, which is basically the blanket federal policy applied at DOD as well.] In the end, the book is very effective at what it does, though it raises many more questions than it answers.

Regarding specific comments of others.... I don't think management was dealt with unfairly here in general. I didn't feel like Cherry was particularly singled out. Also, the book doesn't convey well one factor that I think is important to remember: most of the immediate managers (e.g., Rogers, Capasso) were running large, active research programs of their own. There's no question that between that and the corporate turmoil from the collapse of telecom, these people had other things on their minds than trying to manage Schon. Now, that being said, how in the name of all that is holy did these people not realize that Schon's publication rate was simply unphysical? NO ONE can write a paper every two weeks for two years. Didn't this raise questions at the journals, too? One other comment about management that was raised only indirectly.... There were a number of people who were thrilled to claim (effectively) some share of the credit for this stuff when things looked good, but were quick to disavow all responsibility when things went bad. You can't have it both ways.

(One final point that has nothing to do with the author: the choice to put a silhouette of Icarus on the cover is deeply flawed. Icarus actually flew.)

Anyone read this yet?

I was in Barnes & Noble yesterday evening and saw a copy of Plastic Fantastic in their science section. This is Eugenie Reich's telling of the Schön saga. Anyone out there had a chance to read this yet? Steve? Don? I'll have to pick up a copy at some point.

Wolfram|Alpha: not too impressive.

By now many of you have run across Wolfram|Alpha, billed by its creator as a "computational knowledge engine". I've been goofing around with it a little over the past two days, and I'm not too impressed, though there are some cute things in there. The demonstration video, narrated by Wolfram himself, is very slick, and gives you the impression that Wolfram|Alpha can take even minimalistic requests (e.g., "Germany US GDP") and provide lots of computed output (US and German GDPs side by side as a function of time, in various different currency units and normalizations, for example). That is sort of true, for a very limited subset of queries. As one might expect from the people who developed Mathematica, Wolfram|Alpha can also do some symbolic math, including graphing of functions.

Unfortunately, it would appear that their model is to have these kinds of limited queries templated by hand on their side. Trying to ask well-defined questions about comparatively simple things ("What is the resistance of a wire?"), which you might expect from the demo to call up a pretty set of dialog boxes, etc., instead gives you "Wolfram|Alpha isn't sure what to do with your input." In this particular example, just "resistance of a wire" calls up dialog boxes about US and UK wire gauges and is at least somewhat useful. For a parser to do fine with "resistance of a wire" and gag on "what is the resistance of a wire" is pretty sad these days.

Bottom line: the idea of Wolfram|Alpha is cute, but right now it's entirely too much like playing an old text adventure game:
----
You are facing a brown, wooden door set in a dark green frame. There is a doorbell button here.

>Ring the doorbell.

I do not know how to do that.

>ring doorbell

I do not know how to do that.

>push button

You push the button, and from within the house you hear a distant chime.

Faking APS email not a good way to be taken seriously

Many of us know the joy of getting email from, err, enthusiastic amateurs claiming to have solved all of the great problems of modern physics (often involving the invalidation of quantum mechanics, relativity, or both). This morning's allotment was particularly amusing, though. Subject line: Giant Revolution in the Physics Science. From: [allegedly] aps@aps.org. (Really from someone in Hungary.) It explicitly claims to be a message on behalf of about a dozen physicists (presumably not with their actual permission), including last year's Nobel Laureates. Even better, it asks us all to contact the Royal Swedish Academy (complete with contact information) and pressure them to award the Nobel in physics to a Hungarian physicist who "reinterprets the total known experimental results and uses solely the mathematical apparatus of dynamics and electrodynamics". Amateurishly spoofing email from people is no way to promote yourself....

This week in cond-mat

Two recent arxiv papers caught my eye. I'm not working on graphene, but these are both pretty interesting results.

arxiv:0905.0923 - Mak et al., Observation of an Electric-Field Induced Band Gap in Bilayer Graphene by Infrared Spectroscopy
The authors, from Tony Heinz's group at Columbia, make a field-effect device out of bilayer graphene (identified optically thanks to its particular Raman spectrum) and an electrolyte. As I'd mentioned once before, by using electrolytes it is possible to achieve very large gated charge densities in transistor-style devices. In this case, the authors find that they can turn bilayer graphene from a semimetal-like system (with touching valence and conduction bands at the charge neutrality point) to a semiconductor (as determined via optical measurements), with a band gap induced and controlled by the gate. I need to read more carefully just how this works, but it shows how these kinds of experiments (moving a good fraction of a charge per unit cell around) can alter band structure profoundly.

arxiv:0905.1712 - Li et al., Large-Area Synthesis of High-Quality and Uniform Graphene Films on Copper Foils
This paper, published this week online in Science, may end up being quite important. The authors show that they can grow mostly single-layer graphene on copper supports. Copper can be annealed to produce large (several mm) crystallites, so significant areas of graphene can be made this way, templated with comparatively few defects. The big step here compared to earlier work on growing graphene using Ru or Ni substrates is that the resulting material seems to be self-limiting in thickness because of the mutual solubility limits of C in Cu and Cu in C. The authors can also transfer the graphene to other substrates, including Si chips, a necessary step for any would-be electronics applications.

Star Trek

I saw the new Star Trek movie last night, and it was extremely fun. Great special effects, with nods to all the appropriate elements of the original series. I also loved the score - Michael Giacchino rocks. (Sorry for the wiki link - his website seems to be down.) Sure, the science can be goofy, and the plot has some flaws, but somehow it really felt like old-school Trek in all the right ways.

Talks in 90 seconds

At the workshop I'd mentioned, because of time constraints only 11 of the participants had the chance to give full talks. To try to get a better sense of what everyone else was working on, the organizers let anyone else who wanted to speak give a 90 second talk after dinner on the first night. This was a fascinating exercise, taken in good fun by all involved. The time limit was enforced by a big analog timer with a loud buzz.... As you might imagine, conveying what your group is doing given just 90 seconds is a challenge. About 19 people tried this, using anywhere from one to ten (!) powerpoint slides. It worked surprisingly well, actually. A neat idea.

The workshop experience

I just finished attending a three-day workshop near Washington, DC sponsored by the National Nanotechnology Initiative (and other "participating agencies", since technically the US Department of Defense is not strictly part of the NNI, for reasons which escape me), focused on "nanotechnology-enabled sensing". Since I've only backed into anything sensing related in the last couple of years, this was very educational for me. The workshop was put together, in part, by Roger van Zee from NIST and Gernot Pomrenke from AFOSR, and was tasked with producing a report on the topic. The report is actually supposed to be useful to diverse a diverse audience, from technical contacts at the various agencies to Congressional staffers and the White House Office of Science and Technology Policy. I learned a lot, and met many interesting people from other universities, national labs, industry, and federal agencies.

As you might imagine, producing the report is quite a task. You have to corral 30-40 PhD researchers (who all have their own areas of expertise and writing styles), and build up a consensus document that is comprehensive, readable, brief but with some technical depth, and covers an extremely broad topic. Sensing is particularly tricky, since there are many many transduction mechanisms, many many things that people want to detect (including small molecule chemicals, biomolecules, cells, physical variables, EM radiation), and lots of ancillary requirements (biocompatibility? specificity? portability? low power?). It's like herding cats, but in the end I think this report should do a good job of highlighting what nano can do for sensing. (Here's the five-word executive summary: Sensors good, nanosensors much better. See? Who says that it's tough to write for non-scientists....)

Small really is different

Shameless self-promotion part II. The actual scientific result that just came out in Nature is rather surprising. There are two "ordinary" settings for Kondo physics: a magnetic impurity in an otherwise nonmagnetic host (e.g., dilute Mn atoms in Cu), or a quantum dot containing an unpaired electron. In the former case, the conduction electrons of the host metal can lower their kinetic energy by trying to occupy a singly occupied d orbital of the magnetic impurity. However, because of the Coulomb repulsion of the other electrons on the impurity atom, really doing this is classically forbidden by energy conservation. Still, quantum mechanics lets that forbidden state exist as a virtual intermediate state in a scattering process that takes a conduction electron from the host, flips the spin of the impurity atom, and spits out an electron into a different conduction band state. In the quantum dot case, an analogous magnetic dance takes place, in which the spin of the unpaired electron on the dot is flipped, and an electron is transferred across the dot. This Kondo scattering process affects the electronic conduction through the dot in a particular, identifiable way.

The surprising result in our case is that we see indications of this Kondo process in atomic-scale junctions between chemically homogeneous (e.g., all the atoms are Ni) ferromagnetic metals. The data are pretty clear, and indicate that this spin-related process competes with ordinary ferromagnetic exchange in these nanostructures. It would appear, from accompanying theory calculations by our coauthors, that the very act of whittling the ferromagnetic metal down to the atomic-scale junction is enough to mess with the electronic properties of the metal that we'd ordinarily consider to be intrinsic. The bottom line is, when worrying about the magnetic properties of truly nanoscale structures (with many surface atoms), one may need to keep track of relatively exotic ("strong correlation") physics like the Kondo effect.

An ideal collaboration

I just had about the best possible experience with a collaboration that one can expect to have. Indeed, I worry that I've now used up my "collaboration karma". Here's how these things are supposed to work....

Back at the APS March Meeting in 2006, my student Zach was presenting his masters work on electronic conduction through atomic-scale Ni junctions. Specifically, he had been doing some experiments to try and examine whether atomic-scale contacts between ferromagnetic metals had unusually large changes in electrical resistance when placed in a changing magnetic field, as had been reported in the literature. (We found that the answer is "No", but the magnetoresistance does depend in detail on the precise atomic configuration of the device. This work was independently confirmed simultaneously by Dan Ralph's group at Cornell.) Anyway, at the end of the session, I met Carlos Untiedt, who was just getting going as a faculty member at the University of Alicante in Spain. I'd read some of Carlos' earlier work on metal junctions made using mechanical means, and he'd read our work, too. He mentioned to me that the Spanish government has a program that allows Spanish graduate students to spend time abroad working in other labs, and suggested that we try this at some point. I said that this sounded like a good idea, and we should do it.

Fast forward to the beginning of 2008, when Carlos and I got back in touch. He had a very good student eager and interested to come and visit, and, even better, they had some exciting data that they'd been taking in mechanically-controlled (STM-style, middle of this page) atomic-scale metal junctions. The main advantage of mechanical junctions is that you can break and re-form them many times, giving you serious statistical information about junction properties. Now, in my lab we often use an alternative technique for making atomic-scale junctions that doesn't involve mechanical motion. While our method (electromigration) is more time-consuming and therefore not well suited to really large statistical samples, it has one main advantage: the junctions we make have enough geometric stability that we can look at a single junction over many temperatures. This can't really be done in STM-style junctions. This was a relatively rare situation: there was an ideal point of scientific collaboration, and we had the person and the resources to make things happen.

So, we did it. Carlos' student, M. Reyes Calvo, came and spent a little under four months working in my lab with my group. She was able to make junctions with our approach that were analogous to the ones that she'd been studying in Spain, and measured them as a function of temperature in our system. The results were very nicely consistent with her data from Spain, and the whole scientific story hung together well. After her visit and a number of fun conversations with theorist colleagues at Alicante, a paper was written that came out today in Nature. It just doesn't work any better than that. I'll write about the science in a separate post....

Nice speech.

President Obama addressed the US National Academy of Sciences this morning (video link here). Students, take note. In addition to boosting funding for basic research and making the R&D tax credit permanent, he's talking about tripling (!) the number of NSF graduate fellowships.

Just stop.

Attention TX state and federal officials with R next to their names. Let me clue you in on a couple of points.
1) Secession is not an option. See the US Civil War.
2) TX does not have the authority to break up into smaller states autonomously. That went out the window when TX was re-admitted to the Union after the Civil War.

Bloviating about this pointless drivel makes the entire state look bad. Don't you realize that this garbage makes it difficult to convince smart people to move here, because it looks like the state is governed by idiots?

(This is my last Texas post for a long while - I promise.)

Random favor....

I use the free version of google analytics to do some simple tracking of page views, etc. on both this blog and on my group webpage, just for fun. For some strange reason, the little javascript doodad that allows google to track hits works just fine on all of my group-related pages (like this one and this one), but fails on my publications page. If someone out there with greater expertise or sharper eyes than me could take a look at the html source and explain to me what's wrong with my publications page, I'd greatly appreciate it. Thanks. UPDATE: Thanks - all fixed, I think. Behold the power of teh intarwebs.

Cold fusion, the longer story.

I fully expect angry comments about this....

Here's how a cold fusion experiment is supposed to work, broadly. One takes an electrochemical cell containing either regular water or D₂O, and as one electrode uses palladium (prepared in some meticulous way, to be discussed further below). Then one sets the electrochemical conditions such that hydrogen (or deuterium) ions are electrochemically favored to go into the palladium lattice, up to some very high loading. It's been known for decades that Pd likes to take up hydrogen, so the fact that one can do this is of no surprise. Now, while all this is going on, one carefully monitors the temperatures of the electrodes, the water, etc. The experimental claim, coarsely described, is that after some time, cells containing heavy water under these conditions begin to get hot (but not cells containing ordinary water!). Ideally one does good calorimetry and can measure the amount of energy that comes out of the cell in the form of heat, vs. the amount of energy put in in the form of integrated electrochemical current times voltage. The claim is that in some such experiments, the inferred amount of energy out is much larger than the electrical energy in. This is "excess heat".

So, what's the problem? Well, there are several issues.
1) Calorimetry can be a tricky business. This was the main criticism of the original Pons and Fleischmann work. From what I can tell, people have been much more careful about this than twenty years ago.
2) The experiments just aren't reproducible, in many senses of the term. For example, the temperature-vs-time evolutions of nominally identical cells are completely different, and all over the map. There are big fluctuations on many timescales all over the place. Sometimes the thermal output is big, sometimes it's small. This is generally swept aside by those doing the experiments, who take a wildly fluctuating response, integrate it, and claim reproducibility because the net integral ends up having the desired sign. Not the desired magnitude, just the desired sign. What would I expect to see in a well-controlled experiment? Take one large piece of palladium, cut it into thirds, and set up three identical cells. The temperature-time histories of these things should really reproduce. If you can't do that, then you don't have a controlled experiment. This isn't a small thing.
3) The cells stop working after a while. Unsurprisingly the time period varies from cell to cell. Now, why should this happen unless the underlying process is chemical in some way? By the way, some cells (but not all) "revive" when the electrochemical conditions are changed. Again, all of this is massively variable, even between nominally identical cells in the same labs.
4) The claim of excess heat assumes that there's no chemistry taking place. For example, what if I made that assumption and looked at my car engine? The amount of electrical power input by each spark plug is miniscule compared to the total power out. If I neglected chemical reactions, I'd come to the conclusion that something amazing was going on. Furthermore, if I normalized the output power by, say, the number of platinum atoms at the tips of the spark plugs, I might then conclude that the only way of achieving such power out was something like nuclear. That's the hazard of ignoring possible chemical channels. The issue here is that palladium is known to be highly catalytic, and there are certainly diffusion processes within solids that can be strongly influenced by isotopic differences. Moreover, the claim is also that surface prep of the Pd is of absolutely critical importance. Again, this sounds to me like catalysis, not a bulk effect. Now, you'd think this could all be resolved by analytical chemistry - look at the cell materials before and after running. Look at the water before and after running. However, remember that the different folks doing this disagree on basic analytical chemistry issues like the possible production of helium, tritium, etc. That has to make you wonder about how trustworty their collective analyses are.

Now, I'm not saying that there's nothing worth examining here. The DOD clearly thinks its worth looking into, and it would be nice to get this straightened out once and for all. However, 60 Minutes notwithstanding, the work is just not reproducible in the sense that most experimental physicists would use.