The state of "molecular electronics"

For those interested in the history and current state of "molecular electronics", I refer you to the latest focus issue of Nature Nanotechnology.  Good news for those without subscription access - some good articles are available free of charge:

• Mark Ratner has an historical perspective on the field here.
• Emanuel Lörtscher discusses the challenges of making an actual technology out of these systems. 
• A variety of experts (including me) weigh in with blurbs about where things are and where they are going.
• Sri Aradhya and Latha Venkataraman present an excellent up-to-date review of the field, emphasizing the evolution of measurements beyond just collecting current-voltage characteristics.

Rescheduled, Workshop on Surface Plasmons, Metamaterials, and Catalysis

Three of my colleagues and I are helping to organize a workshop at Rice University on October 21-23, 2013.   (This had originally been planned for May, but sequester-related travel restrictions on the government participants among other things forced a rescheduling.)  The goal of this ARO-sponsored workshop is to explore the opportunities for chemical catalysis arising from recent advances in the fields of metamaterials and plasmonics.  The workshop will bring together scientists from the disciplines of electrochemistry, catalysis, and plasmonics, which have not traditionally had a common platform.





The confirmed invited speakers are:

Rick Van Duyne - Northwestern University
Paul Bohn - University of Notre Dame
Martin Moskovits - University of California, Santa Barbara
Katherine Willets - University of Texas at Austin
Jennifer Dionne - Stanford University
Mark Brongersma - Stanford University
Louis Brus - Columbia University
Harry Atwater - California Institute of Technology
John Yates - University of Virginia
Mengyan Shen - University of Massachusetts, Lowell
Suljo Linic - University of Michigan
Mostafa El-Sayed –- Georgia Tech
Tom Mallouk –- Penn State

Topics include:

• The state of the art in plasmonics, metamaterials, and chemical catalysis
• Areas of catalysis that could benefit from enhanced optical/electromagnetic concepts
• Concepts for nanophotonic- and metamaterials-driven catalysis and heat generation
• Surface nanoengineering to merge nanophotonics and catalysis
• Quantum plasmonics
• Hot electrons driving chemistry
• Chemical sensing using nanophotonic and plasmonic concepts
• Nanophotonic characterization of catalytic structures:  Where do the reactions happen, and how fast?

The deadline for abstract submission is July 21, 2013, and space is limited.  The workshop website is here:  http://PlasEnhCat2013.rice.edu  .

Please feel free to distribute this information to people that would be interested!

What does "heating" mean at the nanoscale?

I've talked before about what physicists mean when they talk about "temperature", and work has me thinking about this a lot these days. Temperature is inherently a statistical concept.  It doesn't really make sense to talk about the temperature of a single electron.  The electron has some momentum (and therefore some kinetic energy), but temperature is not a meaningful concept for a single particle in isolation.  Now, if you have a whole bunch of electrons, you can talk about how many of them have a certain amount of energy.  That distribution of electrons as a function of energy takes on a particular form when the electron system is in thermal equilibrium.  (That is, if the electron system is weakly coupled somehow to an energy reservoir so that energy can be exchanged freely between the reservoir and the electrons.)  When the electron system is in thermal equilibrium with the reservoir, on average no net energy is transferred as a function of time between the electrons and the reservoir; this is what we mean when we say that the electrons and the reservoir have the same temperature.

The situation gets really tricky when a system is driven out of equilibrium.  For example, you can use a battery to drive electrons through some nanoscale system.  When you do that, and you look at different points within the nanoscale system, you will find that, in general, the distribution of the electrons as a function of energy doesn't necessarily look much like the thermal equilibrium case.  So, is there a sensible way to generalize the idea of temperature to quantify how "hot" the electrons are?  The problem is, there are many ways you might want to do this - you are trying to take a potentially very complicated distribution function and essentially summarize it by a single number, some local effective temperature.   A natural direction to go is to consider a thought experiment:  what if you took a reservoir with a well defined equilibrium temperature, and allowed it to exchange energy with the nonequilibrium system at a location of interest.  What reservoir temperature would you have to pick so that there is no net average energy transfer between the system and the reservoir in steady state?   That is one sensible way to go, but in the nano limit the situation can be very tricky, even in the thought experiment.  The details of how the imagined energy exchange takes place can affect the answers you get.  Tough stuff.

Instructor opening at Rice

RICE UNIVERSITY

Wiess Instructorship in Physics and Astronomy

The Physics and Astronomy Department at Rice University invites applications for a one-year instructorship position teaching introductory physics, commencing July/August 2013.  The teaching load is equivalent to two courses per semester.  There would also be opportunities to develop innovative teaching methods and pursue independent research or collaborations with existing research programs (see web page http://physics.rice.edu).  Evaluation of applications will begin immediately and continue until the position is filled. Applicants should send a curriculum vitae, a statement of teaching and research interests, and a list of publications as a single PDF file, and should arrange for three letters of reference to be sent to: vcall@rice.edu with subject line "Wiess Instructorship" (pdf format preferred), or by postal mail to Wiess Instructorship Search, c/o Valerie Call, Physics and Astronomy Department-MS61, Rice University, 6100 Main Street, Houston, TX 77005-1892. Applicants must have a PhD and be eligible to work in the U.S. Rice University is an affirmative action/equal opportunity employer.

Ask me something.

I realized I've never really tried having my readers just post questions for me.   Have at it!

A Scientist Laureate position for the US?

This is at least thought-provoking.  Lamar Smith (R-Texas, chair of the US House science committee, famous for things like this) and Zoe Lofgren (D-CA, about as far from Lamar Smith as I can imagine with the possible exception of Nancy Pelosi) are co-sponsoring a bill that would create a position called Scientist Laureate of the United States.  This person would be appointed by the President following nomination by the National Academy of Sciences, and would be meant to act as an inspirational figure, making public appearances and furthering the cause of science.  This could be a good thing, provided (1) an actual accomplished scientist is chosen, not someone who has to satisfy a political agenda; and (2) the person chosen is charismatic and able to use the bully pulpit effectively.  The Science Laureate should do more than show up at middle schools - they should get major exposure (e.g., late night talk shows; hosting a science program on a major network with actual resources to make it good; having the ear of Congress, perhaps even the limited ability to insist on speaking at a hearing of the House or Senate science-related committees).  (Halftime at the Superbowl is probably out of line.)

While I applaud scientists with great public outreach track records (Neil deGrasse Tyson just spoke at our commencement), that should not be the sole criterion.  If this passes, hopefully Congress will keep in the bit about the NAS making the choice.  Suggestions are invited in the comments.

MOOC followup

Very briefly, here is an open letter by the San Jose State University philosophy department regarding MOOCs (one in particular).   Food for thought.

update:  my colleague Moshe Vardi pointed out his own editorial on this topic.

I don't agree with everything in either of these documents.  I do think it's worth thinking hard about the purpose of MOOCs.  Are they about idealistically providing access to fantastic educational opportunities at very low cost to the student for millions of potential pupils who have an internet connection?  Are they about cynically slashing the operating costs of universities by restructuring the educational experience and potentially eliminating large numbers of faculty jobs?  These are not mutually exclusive.

Fun with single atoms

IBM Almaden research has produced "A Boy and His Atom", a stop-motion movie where the frames are scanning tunneling microscope images of carbon monoxide molecules on the Cu(111) surface.  Here is the "Making of..." movie as well.  Fun stuff.  I was particularly amused by Andreas Heinrich's comment that "if I can get a thousand kids to join science rather than go into law school, I'd be super happy."  Amen :-)

Can Congress please not screw up the NSF? Please?

I just read this article at Science's blog, describing how Lamar Smith, chair of the House science committee, basically wants to gut peer review at the NSF and replace it with something more to the liking of the House Republicans.  This would be catastrophically bad for a large number of reasons.  If they do this, you know it's only a matter of time before they decide to undermine peer review at NIH and DOE Office of Science also.  Gahh.  Can't blog - too incoherently angry.

update:  For what it's worth, this would presumably have a hard time passing the Senate and getting signed into law by the President, though given Congress' tendency to lump zillions of unrelated bills together into giant omnibus legislation, you never know for sure.   NSF is probably not the real long-term target of these types.  Picture what would happen to research if big pharma lobbyists get to have Congress decide what NIH grants should be funded, or if big energy lobbyists do the same for DOE grants (to say nothing of de-funding anything they find politically unacceptable).

Cryogenic dark matter detection, redux

About 3.5 years ago, I posted about the technology used by the CDMS collaboration to look for dark matter using clever solid-state detectors.  These folks have some news that is, as is often the case in any novel particle detection experiment, intriguing but not yet definitive.  This paper is probably the best place to see a summary of the results.  In their CDMS II run, the team had 19 germanium-based and 11 silicon-based detectors (cooled to 0.04 K!) running for five years (2003-2008) in an old mine in Minnesota (to cut down on cosmic ray background).  This paper reports results from the Si detectors, where after a lengthy blind analysis they see three events that look interesting.  Since germanium has a higher atomic number than Si, the idea of running the two materials in parallel was to have a cross-check and provide some information about how the searched-for weakly interacting massive particles (WIMPs) might interact with ordinary matter as a function of energy.  I should also note that the collaboration is now running "SuperCDMS" with a larger mass of germanium (9 kg) since 2011, and will eventually expand up to 200 kg of Ge running in Soudan in Ontario.  It's interesting that their earlier analysis from their Ge detectors reported no candidate events (as far as I can tell), while the analysis of the Si detectors shows three candidate events.  My understanding is that this could have to do with the mass range of the WIMPs, but I would be happy if someone would provide more context in the comments below.  Either way, I think it's great to see how condensed matter physics (and in particular cool device fabrication, as in the superconducting transition-edge sensors used here) can have an impact on Big Questions like dark matter.

MOOCs and online education

Massive open online courses (MOOCs) and concerns about online education are all the rage these days at universities.  There is a growing recognition of a few key points:  The cost of undergraduate education (in the US at least) continues to increase much more rapidly than inflation; online capabilities are sufficiently advanced now that it is possible, for comparatively little investment, to distribute educational content to many thousands of people at very low cost, in principle having a major pedagogical impact (see, e.g., the Khan Academy, to say nothing of MIT's opencourseware); more than one major concern is springing up trying to guide online education at the university level (see, e.g., coursera and edX).  [Note to self:  find some demo as cool as the thermite reaction to hook people into any online course I ever teach.]  There is clearly a major sense of urgency on the part of university administrators.  To belabor an overused analogy, they are worried that the online education train is leaving the station, and they fear the consequences of getting left behind. 

All of these things are true, and I understand the concern.  However, a few points have occurred to me about this, and I'd be happy for some discussion in the comments if people are interested.

1. Many people do not really have the self-discipline to learn in an online-only environment.  I like to think I was a pretty dedicated student (no smart comments from my former classmates, please), and I'm not sure I would have the self-discipline to watch online-only lecture material and do online-only assignments for an entire semester.  Some people do have the personality for this, but I have a hunch that many of them are the same folks who really can check a book out of the library and teach themselves a new subject ab initio.  Most 18 year olds are not like that, and the peer pressure/social environment of having friends physically going to scheduled classes is a major motivator.  Bill Press, when he visited Rice and we chatted about this, pointed out that many people pay real money to take Microsoft online certification courses, and complete them at a high rate.  That's true, but it's also a particular case where the financial benefits of completing that particular course are often very clear to the student, and it's also true that there's a difference between university study and vocational training.
2. It only makes sense to develop online courses where your institution really adds value.  Does anyone think it would be a good idea for every major university to develop their own MOOC for Introductory Calculus?  We could do that, but in the end there will likely be a small handful of truly innovative, extremely well done calc courses.  The market will drive toward some kind of mix-and-match mode of operation (unless the content providers constrain things greatly).
3. The sense of urgency is not unreasonable, but early innovators don't necessarily win the day.  For example, Lycos and Alta Vista were early to the scene in "search", yet comparative latecomer google crushed them.

So, are MOOCs really going to sweep through and destroy the modern university system?  Are physical universities going to become like specialty bookshops and online providers like Amazon?  Let me know what you think.

Book review: Alsos

I just found and read a great book, Alsos, by Samuel Goudsmit. The Alsos mission was the Allied dual scientific/military intelligence gathering expedition following the Normandy Invasion, tasked with learning the status of the German atomic program and rounding up German nuclear scientists. Goudsmit, who with Uhlenbeck helped convince people like Pauli of the usefulness of the concept of spin (the intrinsic angular momentum of particles like the electron), was a Dutch Jew, and while he was in the States working on radar, his parents were sent to a concentration camp and killed. The book is fascinating. It's split between the story of the actual mission (which discovered relatively quickly and much to the relief of all involved that the Germans never even got a nuclear pile to go critical) and an indictment of science and industry in a totalitarian regime. It is quite the cautionary tale of the politicization of scientific research and the arrogance of some physicists (Heisenberg fares particularly poorly, to the surprise of no one), told with a wry sense of humor. Highly recommended.

 

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Workshop on "Electronic Properties of Carbon-based Nanostructures"

I'm on my way back to the US from this workshop at the Universität Regensburg.  It was a fun and interesting meeting, and the quality of the invited talks was uniformly high.  The city was also very neat.  I'd had no idea that it had managed to escape (almost completely) Allied bombing during WWII, so as a result it has many buildings dating back to the Middle Ages.  

On the science side, it was particularly nice to hear some talks from and meet a number of people that whose work I've seen over the years but I'd never met face-to-face before.  For example, Steven Louie (linking to wikipedia since all of the Berkeley servers are inexplicably slow right now) spoke about ways to accurately calculate the optical properties of graphene (including electron-hole interactions properly). Philip Collins showed how it's possible to look at single-molecule biophysics (like the functioning of individual enzyme molecules) by anchoring the molecules of interest to single-walled carbon nanotubes, where the action is transduced into changes in the conductance.  Adrian Bachtold gave a nice overview of their work on optomechanics of nanotubes, which has enabled them to do mass sensing at the resolution of a single atomic mass unit (10^-27 kg) and force sensing with similarly impressive sensitivity.  Richard Berndt from Kiel discussed his group's work where they argue that light emission from STM tips shows the signature of shot noise in the current at optical frequencies.  Wolfgang Wernsdorfer, grand poobah of molecular magnetism, presented new results showing amazing control and detection of individual electronic spin lifetimes (in Tb-containing molecules).  For a spin to flip spontaneously, the molecule has to transfer angular momentum to the rest of the world somehow.  In the new experiment, this happens by dumping angular momentum into a carbon nanotube to which the molecule is anchored.  Since the allowed vibrational states of the nanotube can be controlled, this in turn tunes the spin flip rates.  Finally, Klaus Müllen gave an overview of ways to rationally synthesize, by chemical means, graphene flakes, ribbons, and other shapes.  The chemistry is just unreal.

Spin Hall physics

As I mentioned during the APS meeting, Dan Ralph presented some beautiful work (for example) on spin torque devices (where the flow of spin-polarized electrons is able to rotate the magnetization of some "free" ferromagnetic layer of material).  This spin torque business is a fairly mature idea, and the early demonstrations of this effect made use of layered structures (ferromagnet/normal metal/ferromagnet), with the current flowing perpendicular to the layers.  That is, if electrons flow from FM1, some of them are spin-polarized because of the magnetization of FM1, and those polarized electrons traverse the normal layer into FM2.  That works fine, but the most angular momentum you're ever going to transfer that way is \( \hbar/2 \) per electron, and that assumes that the electrons from FM1 are perfectly polarized.   Suppose you could do better than this.  Is there some way, for a given amount of charge current that you flow, to get more angular momentum transferred?

The answer is "yes", and the key is to leverage the spin Hall effect.  (For a good summary of spin Hall physics, see this paper by one of the progenitors of the field - I'll briefly summarize.)  In the regular Hall effect, we think about charge current flow in a plane in the presence of a perpendicular magnetic field.  The charge carriers experience a Lorentz force from the magnetic field that pushes them in the plane transverse to the direction of the (longitudinal) charge current.  Net charge of one sign piles up at one transverse edge of the sample, and net charge of the other sign piles up at the opposite edge, until the force from the resulting transverse electric field balances the Lorentz force.  (Glad to see wikipedia has fixed the figure in this article.  A few years ago they had the direction of the Lorentz force backward.)  In the spin Hall effect, we again think about current flow in a plane.  However, there is no external magnetic field.  Instead, we have the current flowing in a material with strong spin-orbit scattering (that is, in the reference frame of the moving electron, the effective charge current due to the nuclei seemingly moving by produces enough of a magnetic field in that frame to couple significantly to the spin of the electron.  Fundamentally this is a relativistic effect!).  Because of the coupling of spin to orbital motion, if the charge carriers scatter, the spins self-polarize; spin-"up" electrons will pile up on one transverse edge of the sample, while spin-"down" electrons will tend to pile up on the opposite edge.  The extent to which this happens is determined mostly by the strength of the spin-orbit coupling, which is larger in heavier atoms.

So, Ralph and coworkers have used this effect to great advantage.  Instead of the FM/N/FM layered structure, they make a structure that looks like SO/FM/N/FM, where SO is a strong spin-orbit material, such as tungsten or platinum.  They can flow a current within the plane of the SO layer.  Through the spin Hall effect, this can pump polarized spins perpendicular to the plane, into the adjacent FM layer.  (The electrical resistance vertically through the FM/N/FM stack is a way of monitoring the relative alignment of the FM layers, thanks to the giant magnetoresistance.)  This is particularly clever, because for strong SO coupling in the SO layer, thanks to the large contact area at the SO/FM interface, they can get more like 10 \( \hbar \) of angular momentum per electron flowing within the SO layer.   Fascinating to realize that these effects (because they originate from SO physics) are really dramatic experimental proof of the way electric and magnetic fields obey special relativity!

Vanadium dioxide and ionic liquids

Before posting about the APS topics I'd mentioned, I wanted to write a bit about a recent paper that has received quite a bit of attention.  Stuart Parkin's group at IBM Research in Almaden reported in Science last week that they had used an ionic liquid to alter the properties of the strongly correlated oxide VO₂.  As I'd written previously, VO₂ has a metal-insulator transition at 67 C in the bulk, and there has been much interest in using some kind of electrical means to trigger the transition from the insulating to the metallic state in such correlated oxides.  If the insulating state results from Mott physics (i.e., the on-site electron-electron repulsion in the half-filled d band is so strong that the electrons cannot doubly occupy any of the transition metal sites, and the system acts like an insulator even though it would be a metal in the absence of the Coulomb repulsion), then electronically tuning the system away from half-filling (e.g., with a gate using the field effect) could switch the system into the metallic state.  Such a MottFET would be a switch operating on principles very different from those used in conventional Si transistors, and could in principle have superior operating characteristics (for the experts, things like subthreshold swing).   In the Parkin group's work, however, they report pretty compelling evidence that the switching in their system is driven by electrochemistry rather than simple electrostatic doping.  They argue that the metallic state that they produce results from chemical reactions between the VO₂ and the gate-biased ionic liquid that pull oxygen atoms out of the VO2 film.  The evidence for this is that a film treated this way recovers the insulating state when properly exposed to oxygen.  Moreover, they can expose the device to a specific isotope, ¹⁸O.  They can then sputter material off the film and use mass spectrometry to "weigh" the fragments (secondary ion mass spectrometry), and they find evidence that ¹⁸O makes it into the film to a depth of tens of nanometers (many unit cells). 

I find three things interesting about this paper.  First, the actual science is very nice, and I like the isotope tagging/SIMS quite a bit.  Second, I found the perspective put on this by IBM (and the resulting media coverage) a bit surprising - that using liquids and ion motion was a major advance because it would allow chips that operate more like the brain (history dependence = learning, + nonvolatile state retention).   I think that's a surprising spin to put on this.  That brings me to my third point, the true significance of the paper in (part of) the CM community:  This shows that you have to be very very careful when playing with ionic liquids to avoid electrochemistry!  There are previous papers out there that show very modest response of VO₂ in some forms to ionic liquid gating (here and here, for example), and a high profile Nature paper from last summer that reports a huge response.  The present work places these prior publications in an important context, calling into question the relative importance of electrostatics vs. electrochemistry. 

APS March meeting, day 4 (and wrapup for me)

Due to the constraints of real life, the March Meeting was over for me yesterday afternoon, but I did see a few more interesting talks.

In the morning, I went to the session about valley polarization in transition metal dichalcogenides That's quite a mouthful, and demands some explanation.  In a number of materials (including dichalcogenides like MoS₂), the conduction band has more than one energy minimum (or valley) as a function of electron momentum.  In MoS2, there are two energetically equivalent valleys.  Achieving "valley polarization" refers to exciting electrons in only one of those valleys.  Why would you care?  Well, any way of labeling your charge carriers is potentially a means of storing and manipulating information.  In materials like these but possessing broken inversion symmetry (that is, the material has a built-in directionality due to its structure), it is possible to do clever things with circularly polarized light to populate a valley preferentially.  In materials with strong spin-orbit coupling, it is then possible to manipulate spin through valley selection, etc.  The talk by Wang Yao did a very clear job of explaining all this pedagogically, and later talks in the session were also good.

I tried to check out an invited talk on resistive memories, but the chair had let the session fall 15 minutes behind schedule in the first hour.  Note:  there is a reason for timers, and if you're going to be a session chair, you have to hold people to their allotted slots.

I did make it to John Martinis' talk about whether materials are good enough to build a superconducting quantum computer.   It sounds like there is cause for cautious optimism, but wow is it going to be a difficult engineering task.  I need to look up how surface coding is supposed to work.

Finally, I finished off my time at the meeting by going to a session on science and public policy.  Unfortunately this was a depressing way to leave things, since the general message in the end was that Congress is truly dysfunctional, with little hope for any bipartisan support for science - in part because of reflexive opposition, and in part because a significant fraction of the Republican base literally does not believe that science is a valid tool for shaping policy.

One final note for the APS planners in future years:  Please make sure that the APS webserver for the meeting site can actually handle the load.  Still, all in all, a good meeting.

APS March meeting, day 3

Yesterday was again a mix of talks (including three from my group), chatting with friends and colleagues, looking around the vendor show (nice toys, and books, including the new edition of Purcell (and Morin) in SI units, and an intriguing graduate E&M text by Zangwill intended as a replacement for Jackson that focuses more on physics than on special functions), and answering email.

One session that was particularly fun was dedicated to artificial quantum matter. This topic is again worthy of a dedicated blog post that I will write sometime soon. The basic idea for the first few talks is a simple one: we know a number of different ways to impose spatially dependent potential energies on electrons constrained to move in 2d. (Note that while it is often convenient to act like the electrons in 2d electron gas or 2d surface states are free, as always this is shorthand for the true situation, where the single particle states are really Bloch-like states that exist due to the underlying periodic potential from the atoms). For example, if you impose a hexagonal lattice of potential wells on the free electrons, you get an effective band structure that looks like that of graphene. This has been done by etching on top of semiconductor structures, and by arranging molecules on the surface of Cu (as I'd mentioned here a year ago, work by Hari Manoharan). Making deeper potential wells gives you the chance to try to create an engineered system analogous to Mott insulators.

Another flavor of artificial quantum matter was discussed by Andrew Houck. If you make a little microwave resonator (a piece of stripline, superconducting to minimize loss), and then add in a superconducting quantum bit to act as a nonlinear element, you can have an effective photon-photon interaction in the cavity. Now consider wiring up a coupled network of such cavities, where the photons feel each other in each cavity and have some hopping from cavity to cavity. This raises the possibility of making "insulating" states of photons. As the speaker said, it's condensed matter without matter. Very thought provoking.

 

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APS March Meeting, day 2

Yesterday I spent much of the meeting talking with collaborators and old friends, and seeing some invited talks at the sessions associated with some of the APS prizes. There were several really excellent talks.

The first that really stood out was Daniel Fisher's talk on the occasion of his winning the Onsager Prize. Fisher is a statistical mechanician, and he gave a very clear all about randomness, using domain walls in random magnets as an illustrative case for his ideas. In ferromagnets, there is an energetic cost associated with having a domain wall between regions of differently oriented magnetization. That acts like a surface tension, with the system tending to try to minimize the length of such a boundary, all other things being equal. Now if you allow the magnetic coupling between neighboring spins to have a random variation, the domain walls take on funny shapes, "finding" the lowest exchange locations because that also lowers the energy cost. Fisher talked about the statistical physics of this system, including the characteristic slow, history dependent kinetics of equilibration. The tails of the distribution of exchange values are really important here. Fisher then finished up talking about evolution as a statistical mechanics problem, where instead of minimizing an energy, the system tries to maximize "fitness", which is essentially the difference between birth and death rates.

The other talks that were exceptional were those in the Buckley Prize session. The prize this year was awarded to John Slonczewski, who predicted, quantitatively, the existence of the effects of spin transfer torque, which I've indirectly discussed before. Since spin really is angular momentum, flowing a spin polarized current into a magnetized material exerts a torque on the magnetization, if the flowing spins are not aligned with M. This is a way of using currents to cause magnetic domains to precess (ferromagnetic resonance) or flip altogether. Luc Berger gave a very good talk outlining the history of this field in a very pedagogical way, harkening all the way back to work done eighty years ago. Dan Ralph in the same session spoke about their incredibly beautiful results demonstrating all of these effects with quantitative agreement with theory. Further, Ralph showed how one can pump spin currents like this and drive such systems using the spin Hall effect rather than just direct current flow. That's worthy of a blog post all of its own, which I will do sometime soon.

 

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APS March Meeting, Day 1

It's that time of year again, when I get together with thousands of my closest condensed matter physics friends to hear and give talks, swap gossip, and swill overpriced coffee. This year the action is in Baltimore, where one of my main observations after the first day is that someone needs to label the correct room lighting setting so that the project images aren't really washed out.

Real life has intruded in a couple of ways on the meeting this year for me, so my posting will likely be more brief than in past years - sorry.

Yesterday I spent most of my time in the sessions on nickelates and vanadates. The nickelates are a very interesting system, of the form RNiO3, where R is a rare earth atom. These form a family of strongly correlated oxides, where electron-electron interactions can be extremely important in determining the properties. The key is the partially filled d band from the Ni atoms, each of which is octahedrally coordinated by oxygens. Depending on the rare earth ion, the Ni-O bond angles change, and there can be two inequivalent Ni sites. Simple band structure without interactions says these should be metals, and LaNiO3 is a (correlated) metal. However, other members of the family are more complex, such as NdNiO3, which has a metal insulator transition in the bulk at around 200K, between a high T paramagnetic metal and a low T antiferromagnetic insulator - some flavor of the Mott transition. I heard a very interesting talk by Greg Fiete from UT about the possibility that one can use interactions in these materials to create new topological insulators, ones where the energy gap that makes them insulating is an interaction-based gap (as opposed to ordinary TI materials, where they are boring band insulators).

The vanadate sessions were also pretty compelling. VO2 also has a metal-insulator transition, this one at 340K, where interactions and lattice distortions both play very important roles. There were many good talks, including one about some extremely pretty work to figure out the triple point of the phase transitions between rutile and two monoclinic phases. There were also multiple talks about manipulating the transition via chemical doping and field effect approaches. Fun stuff.

Other observations so far: lots of sessions on topological materials, lots of sessions on experimental approaches to quantum bits, and lots of worried discussion of the sequester.

 

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Interesting links

Time to play catch-up.  Here are some interesting links I've seen recently.

How to get a faculty offer - a lecture by John Guttag of MIT to their comp sci graduate students.  Not everything translates to the physics/chem/materials/nano communities, but much of this is great advice.  Thanks to Jen Rexford for bringing this to my attention.

A related post from the FSP about the faculty search process. 

An editorial/blog post at Scientific American about the importance of basic research and the painful choices being faced in the US right now.  It contains some choice quotes from Marc Kastner, a great physicist and current dean at MIT.

A very weird article from the Guardian, essentially taking some secular popularizers of science to task for trying to inspire a sense of wonder.  I had no idea that inspiring a sense of wonder was entirely the purview of the clergy.

A Swiftian editorial in the Journal of Cell Science, decrying blogging efforts to point out suspicious (at least to some) figures in scientific papers.  While it's sensible to have some concerns about how blogs are used in this way, I think this editorial is way off the mark.