## Wednesday, September 25, 2013

### DOE ECMP PI meeting, day 2 - things I learned

Very brief list of things I learned about during day 2 yesterday:
• Due to optical nonlinearities, it is possible to get broadband negative (left-handed, that is) refraction from (18 layer thick) graphene.
• In a strong perpendicular-to-plane magnetic field, you can detect (optically) evidence of 1-d subband formation and e-e interactions.
• The optical properties of graphene are very very rich.  That is, complicated.
• Doug Hofstadter was right.
• With an in-plane magnetic field, you can see physics that looks like the quantum spin Hall effect in single-layer graphene.
• Trying to tune the bandgap of GaAs down to 1 V via nitrogen doping without killing the mobility is very hard.
• Ballistic phonon pulses are a very cool way of detecting defects and interface roughness basically with sonar!
• You can measure the exchange field between a magnet and electrons in a superconductor if you can work with ultrathin films (field in plane).
• There are still some weird issues associated with electronic decoherence in the mesoscopic world - coherence times seem to saturate at the lowest temperatures in various etched semiconductor and bismuth nanowires.
• Pumping spin currents via the spin Hall effect is still cool.
• Electronic heating above the lattice temperature in graphene is more complicated than it would appear.
• Anisotropy in the electronic structure at B=0 leads to modified anisotropy in composite fermions at $\nu = 1/2$.
• The $\nu = 5/2$ quantum Hall state is surprisingly robust as mobility goes down.  That means that short-range, high-angle scattering doesn't really kill the state, which is good, and that mobility as our favorite proxy for sample quality is a poor guide in this regime, which is interesting.
• My colleague Rui-Rui Du has a really great and exciting system for looking at topological edge states and quantum spin Hall in InAs/GaSb quantum well structures available from a commercial vendor.

## Tuesday, September 24, 2013

### DOE ECMP PI meeting, day 1 - things I learned

Yesterday was an extremely dense meeting day.  Many talks, many posters.  By its nature, this meeting is far more technical than the Packard meeting, so the bullet points below are going to be more obscure to the nonexpert.  The program is here.  Among the things I learned yesterday:
• Harold Hwang continues to do very interesting physics at the interface between LaAlO3 and SrTiO3, looking at fundamental issues like the limits of charge mobility in the 2d electron gas there, and how to make delta-doped bilayers.
• Many other people are playing with oxide and pnictide MBE, making pnictide superlattices, strain-controlled pnictides, multiferroic films, etc.
• It is possible to use the elastic deformation of VO2 at the metal-insulator transition to alter the magnetic coercivity of an overlying Ni layer.
• In strained films, it is possible to see through x-ray techniques that one can decouple the electronic transition in VO2 from the structural transition.
• Real progress has been made recently in using engineered structures of nanomagnetic patterns to model complex systems like spin ice.
• Nd2Fe14B, the rare-earth hard magnet, can take up hydrogen into its open structure, and when it does, the lattice expands, which greatly softens the magnetic response.
• Mott insulating materials can be synthesized that exhibit quantum criticality at zero magnetic field and as-made.
• Iridates are interesting and complicated.
• Investing in developing a particular technique (in this case, NMR of unusual elements like oxygen, sodium, and arsenic) can pay big long-term dividends in terms of unique experimental insights (e.g., there are no "static loop currents" flowing in the cuprate superconducting state).

## Monday, September 23, 2013

### DOE experimental condensed matter physics principal investigator meeting

I am spending the next 2.5 days at the DOE's experimental CMP principal investigator meeting in the Washington DC area.  I'll try to blog a few highlights over the course of the meeting.  The basic idea is supposed to be to get all of the PIs together to talk about their latest stuff, and ideally to foster new collaborations and activities.  Judging from the people sitting around me, it looks like this will be an extremely strong meeting in terms of science.

## Sunday, September 15, 2013

### Things I learned this week at the Packard meeting

For the 25th anniversary of the amazingly awesome David and Lucille Packard Foundation fellowships, I was fortunate (and as always very grateful) for the opportunity to go to their annual meeting and listen to talks from incoming and outgoing Fellows.  These meetings are tremendous - a very rare chance to hear 20 minute talks on topics across science, engineering, and math, aimed at the technically literate non-expert.  Back in the dim past of this blog, I've posted about these before (here, here, and here).  Here are some take-away facts I learned this time around:
• By very narrow targeting of specific pathogens, it might be possible to remove some of the evolutionary pressure (exerted by horizontal gene transfer [something I'd never learned about] from your gut bacteria) that leads to antibiotic resistant strains.
• It's possible to use ideas from superresolution microscopy and principal component analysis to improve structure determination in materials characterization.
• Using small molecule dyes, it is possible to use optical processes to turn the tables on some chemical reactions, favoring "anti-Markovnikov" selection, rather than Markovnikov rules (where reaction sites are determined by permanent dipole moments of bonds).
• Sometimes cells can recognize themselves (and distinguish between themselves and close relatives) using proteins based only on one or two genes.
• I'm used to thinking about coupling two (identical) resonators and getting an energy splitting (like bonding/antibonding orbitals).  I hadn't realized that using an effectively imaginary coupling means you can get a lifetime splitting (one long-lived, one short-lived mode).
• You can tie vortex rings in knots.  Watch the videos!
• Greenland has not been ice-free for at least 350,000 years, and radioactive dating based on dust captured in the ice makes it possible to untangle even faulted or folded ice cores.
• Monsoons are complicated, even if you model a completely water-covered idealized planet.
• Every time a pair of neutron stars collide, they produce about one Jupiter mass worth of Au, while a core-collapse supernova makes about one lunar mass worth of Au.  As a result, even though colliding neutron stars are rare, half of the gold out there came from them.  (In case you were wondering, in all of human history we have mined about 165,000 tons of Au.)
I've left out many others.  As always, very cool.

## Friday, September 13, 2013

### Ionic liquids and gating - how much is chemistry?

I've written before (here, here and here) about the use of ionic liquids in condensed matter physics investigations.  These remarkable liquid salts, with small organic molecules playing the roles of both positive and negative ions, can be used in electrochemical applications to generate extremely large surface charge densities near electrode interfaces.  Many experiments have been published in the last few years in which ionic liquids are meant to induce (via capacitive coupling) large densities of mobile charge carriers within interesting solids at the solid/ionic liquid interface.

One concern in these experiments has been the role of surface chemistry.  While the molecular ions themselves are intended to be stable over a large range of electrochemical conditions, the ionic liquids can dissolve more reactive species (like water).  Likewise, recent experiments by Stuart Parkin of IBM Research have shown that in some systems (vanadium oxide in particular), under certain electrochemical conditions it would appear that ionic liquids can favor the formation of oxygen vacancies in the adjacent solid.  Since oxygen vacancy defects in many oxide materials can act as dopants, changing the concentration of charge carriers, one must be extremely careful that any measured changes in electronic properties are really from electrostatics rather than effective chemical doping.

These concerns can only be ratcheted higher by the simultaneous online publication of two more papers from the Parkin lab, this one in Nano Letters (on SrTiO3) and this one in ACS Nano (on TiO2).  In both systems, the authors again find evidence that changes in oxygen stoichiometry (rather than pure electrostatic charging) can be extremely important in generating apparently metallic 2d surface layers.

This is a very subtle issue, and the gating experiments remain of great interest.  Unraveling the physics and chemistry at work in all the relevant systems is going to be a big job, with a strong need for in situ characterization of buried solid-liquid interfaces.  Fun, challenging stuff that shows how tricky this area can be.

## Thursday, September 12, 2013

### New big science prizes - time for nominations and opinions

There are large, endowed prizes in a number of disciplines.  The most famous of all are the Nobel prizes, of course, and in the sciences at least (chemistry, physics, and medicine), being awarded a Nobel is a singular crowning achievement.  A huge amount has been written about the Nobels - if you want to learn how they came to be, and at the same time become extremely disillusioned about the process for the early awards (my goodness I hope it's better these days - it seems like it must be), I recommend The Politics of Excellence.   The purpose of the Nobel is to reward a major, transformative (to use the NSF's favorite word) intellectual achievement.  The money is not meant to be a research grant.  (Similar in spirit is the Fields Medal for mathematics, though that is much less money and purposefully directed at younger researchers.)

The MacArthur Fellowships are another well-known set of awards.  These are known in popular parlance as "Genius Grants", and unlike the Nobels are (apparently) intended not so much as a financial reward, but as a liberating resource, a grant that can provide the winner with the financial freedom to continue to excel.  In some disciplines (the arts and the humanities in particular) this can completely change the financial landscape for the winners.   Awards that go directly toward furthering the creative ends of the recipients are clearly great things.

In recent years, a couple of new, very large awards have been created, and it's interesting to consider whether this is a good thing.  The Kavli Foundation is awarding prizes every other year in Neuroscience, Astrophysics, and Nanoscience.  To nominate someone, see here.   In spirit, these seem much like the Nobels, with awards so far going to extremely well regarded people, and not meant to function as direct research support.

In more flamboyant style, Yuri Milner has endowed the Fundamental Physics Prizes, also not meant to function as research grants.    What really distinguishes these latest, apart from the sheer magnitude of the awards (\$3M each), is that they have largely gone to high energy physics theorists whose work has not been confirmed by experiment (in contrast to theoretical physics Nobel awards).  More recently there has been a special award to the LHC experimentalists, and some related prizes to condensed matter theorists.  However, the idea of giving very large prizes for unconfirmed theoretical work is controversial.  In essence, is something a "scientific breakthrough" if it's not confirmed by experiment, or is it very exciting math?  Perhaps this is just a labeling issue, but it is hard not to be unsettled by the willingness of some to try to detach science from experimental tests.

Is the scientific community better off from having more of these kinds of prizes?  Certainly it makes sense to consider awards for fields not recognized by the Nobel Foundation.  Nobels have gravitas because of their long established history, but that does not mean that there shouldn't be an analogous prize for, e.g., computer science.  Likewise, anything positive about the sciences that gets public attention is probably a net good.  However, prizes will lose their meaning if there are too many, and making some of them destabilizingly large amounts of money is not necessarily great.   It's also not clear quite what the point is if the same people win multiple large prizes for the same work.   For example, it's credible that Alan Guth could win a Nobel in addition and a Kavli astrophysics prize in addition to the Fundamental Physics prize.    I always tell would-be scientists not to get into this if they're after the big prize at the end - that's not the point of the enterprise, and I'd hate to see that change.  It's also hard for me to believe that the existence of these prizes is going to get the public or students materially more interested in the sciences.   Somehow prizes that go toward helping people continue their work or recognize a career of achievement seem more sound to me, but I remain ambivalent.

## Monday, September 02, 2013

### How to: Carry on a scientific collaboration

I'm writing this at the suggestion of a commenter on my previous how-to post, who was specifically interested in experiment/theory interactions.  Collaborations, as a fundamentally personal endeavor, are as varied as the people who collaborate.  Over the years I have collaborated with a number of theorist colleagues as well as fellow experimentalists, and generally it's been a very positive set of experiences, both scientifically as well as personally.  The main recommendations I can make about collaboration:
• Discuss and plan the ground rules at the beginning.  How is the collaboration going to work?  Is this the sort of collaboration that requires regular discussions and updates?  Are physical samples being sent by one party to another?  Which people are going to be responsible for what tasks?  What are peoples' expectations of authorship (recognizing that occasionally work may take an unanticipated turn, and someone's contribution may grow or shrink along the way)?  Are there restrictions about the samples or data?  (For example, a materials grower might collaborate with person A and person B on different projects; it could be very awkward if person A took samples and then on the side started working on the same project as person B!)
• Collaborate with people who have a similar approach to research projects as you, in terms of rigor, timeliness, and seriousness.  This is true whether those people are your own group, or outside collaborators.
• Make sure to understand what your collaborators are actually doing.  Collaborations are a chance for you to learn something, since presumably you're working with these people because they bring something to a project that you can't do your self.  Sometimes asking what might seem at first glance a silly or naive question can lead to discussion that is informative for everyone.
• Have realistic expectations.  On the sociological level, realize that no one is going to retool their entire research enterprise or retask several people for your sake.  On the scientific side, know what can and can't be done by your collaborators and their techniques.
• Be communicative.  Keep your collaborators in the loop and up to date on what's going on.  If there is a big delay on your end for some reason, let them know.  You'd want them to do the same.  If you have decided that you don't think the project is going to work, or it's not working as anticipated, bring this up and don't let it sit.
• Be a finisher.  The most successful grad students are the ones who actually finish tasks and projects.  In the same way, don't let things slide.  If your collaborator wants you to read through a draft, or you promised to get some data to them in time for some deadline, follow through.