One nice bit of condensed matter/nanoscale physics news:  This year's Wolf Prize in Physics has gone to three outstanding scientists, Jim Eisenstein, Moty Heiblum, and Jainendra Jain, each of whom have done very impactful work involving 2D electron gases - systems of electrons confined to move only in two dimensions by the electronic structure and alignment of energy bands at interfaces between semiconductors.  Of particular relevance to these folks are the particularly clean 2D electron gases at the interfaces between GaAs and AlGaAs, or in GaAs quantum wells embedded in AlGaAs. A thread that connects all three of these scientists is the fractional quantum Hall effect in these 2D systems.  Electrons confined to move in 2D, in the presence of a magnetic field perpendicular to the plane of motion, form a remarkable system.  The quantum wavefunction of an electron in this situation changes as the magnetic induction \(B\) is increased.  The energy levels of such an electron are given by \((n+1/2)\hbar \omega_{c}\), where \(\omega_c \equiv eB/m*\) is the cyclotron frequency.  These energy levels are called Landau Levels.  The ratio between the 2D density of electrons and the density of magnetic flux in fundamental units (\(B/(h/e)\)) is called the "filling factor", \(\nu\), and when this is an integer, the Hall conductance is quantized in fundamental units - see here.   Figure 4 from this article by Jain, with \(R_{xx}(B)\) data from here.  Notice how the data around \(B=0\) looks a lot like the data around \(\nu = 1/2\), which looks a lot like the data around \(\nu=1/4\).  A remarkable thing happens when \(\nu = 1/2\) - see the figure above.  There is no quantum Hall effect there; in fact, if you look at the longitudinal resistance \(R_{xx}\) as a function of \(B\) near \(\nu = 1/2\), it looks remarkably like \(R_{xx}(B)\) near \(B = 0\).  At this half-integer filling factor, the 2D electrons plus the magnetic flux "bundle together", leading to a state with new low-energy excitations called composite fermions that act like they are in zero magnetic field.  In many ways the FQHE looks like the integer quantum Hall effect for these composite fermions, though the situation is more complicated than that.  Jainendra Jain did foundational work on the theory of composite fermions, among many other things. Jim Eisenstein has done a lot of great experimental work involving composite fermions and even-denominator FQH states.  My postdoctoral mentor, Bob Willett, and he are first two authors on the paper where an unusual quantum Hall state was discovered at \(\nu = 5/2\), a state still under active investigation for potential topological quantum computing applications.   One particularly surprising result from Eisenstein's group was the discovery that some "high" Landau level even-denominator fillings (\(\nu = 9/2, 11/2\)) showed enormously anisotropic resistances, with big differences between \(R_{xx}\) and \(R_{yy}\), an example of the onset of a "stripe" phase of alternating fillings.   Another very exciting result from Eisenstein's group used 2D electron gases in close proximity parallel layers and in high magnetic fields, as well as 2D electron gases near 2D hole gases.  Both can allow the formation of excitons, bound states of electrons and holes, but with the electrons and holes in neighboring layers so that they could not annihilate each other.  Moreover, a Bose-Einstein condensation of those excitons is possible leading to remarkable superflow of excitons and resonant tunneling between the layers.  This review article is a great discussion of all of this. Moty Heiblum's group at the Weizmann Institute has been one of the world-leading groups investigating "mesoscopic" physics of confined electrons in the past 30+ years.  They have performed some truly elegant experiments using 2D electron gases as their platform.  A favorite of mine (mentioned in my textbook) is this one, in which they make a loop-shaped interferometer for electrons which shows oscillations in the conductance as they thread magnetic flux through the loop; they then use a nearby quantum point contact as a charge sensor near one arm of the interferometer, a which-path detector that tunably suppresses the quantum interference.  His group also did foundational work on the use of shot noise as a tool to examine the nature and transport of charge carriers in condensed matter systems (an idea that I found inspiring).  Their results showing that the quasiparticles in the fractional quantum Hall regime can have fractional charges are remarkable.  More recently, they have shown how subtle these measurements really can be, in 2D electron systems that can support neutral excitations as well as charged ones. All in all, this is a great recognition of outstanding scientists for a large volume of important, influential work. (On a separate note:  I will be attending 3+ days of the APS meeting next week.  I'll try to do my usual brief highlight posts, time permitting.  If people have suggestions of cool content, please let me know.)

Non-blog life has been very busy, and events have been changing rapidly, but I thought it would be a good idea to give a brief bulleted list of updates regarding the NSF and associated issues: A court decision regarding who has the authority to fire probationary federal workers has led to the NSF hiring back 84 of the employees that it had previously dismissed, at least for now.  The Office of Personnel Management is still altering their wording on this. There is likely some kind of continuing resolution in the offing in Congress, as the current funding stopgap expires on March 14.  If a CR passes that extends to the rest of the fiscal year (Sept 30), that would stave off any big cuts until next FY's budget. At the same time, a number of NSF-funded research experience for undergraduate programs are being cancelled for this year.  This is very unfortunate, as REU programs are many undergrads' first exposure to real research, while also being a critical mechanism for students at non-research-heavy institutions to get research experience. The concerns about next year's funding are real.  As I've written before, cuts and programmatic changes have been proposed by past presidents (including this one in his first term), but historically Congressional appropriators have tended not to follow those.  It seems very likely that the White House's budget proposal will be very bleak for science.  The big question is the degree to which Congress will ignore that.   In addition to the budget, agencies (including NSF) have been ordered to prepare plans for reductions in force - staffing cuts - with deadlines to prepare those plans by 13 March and another set of plans by 14 April.  Because of all this, a number of universities are cutting back on doctoral program admissions (either in specific departments or more broadly).  My sense is that universities with very large components of NIH funding thanks to medical schools are being particularly cautious.  Schools are being careful because many places guarantee some amount of support for at least several years, and it's difficult for them to be full-speed-ahead given uncertainties in federal sponsor budgets, possible endowment taxes, possible revisions to indirect cost policies, etc. Enormous uncertainty remains in the wake of all of this activity, and this period of comparative quiet before the staffing plans and CR are due is an eerie calm.  (Reminds me of the line from here, about how it can be unsettling when a day goes by and you don't hear anything about the horse loose in the hospital.) In other news, there is a national Stand Up for Science set of rallies tomorrow.  Hopefully the net impact of this will be positive.  The public and our legislators need to understand that support for basic science is not a partisan issue and has been the underpinning of enormous economic and technological progress.

An early physics demonstration that many of us see in elementary school is that of static electricity:  an electrical insulator like a wool cloth or animal fur is rubbed on a glass or plastic rod, and suddenly the rod can pick up pieces of styrofoam or little bits of paper.  Alternately, a rubber balloon is rubbed against a kid's hair, and afterward the balloon is able to stick to a wall with sufficient force that static friction keeps the balloon from sliding down the surface.  The physics here is that when materials are rubbed together, there can be a net transfer of electrical charge from one to the other, a phenomenon called triboelectricity.  The electrostatic attraction between net charge on the balloon and the polarizable surface of the wall is enough to hold up the balloon.   Balloons electrostatically clinging to a wall, from here. The big mysteries are, how and why do charges transfer between materials when they are rubbed together?  As I wrote about once before, this is still not understood, despite more than 2500 years of observations.  The electrostatic potentials that can be built up through triboelectricity are not small.  They can be tens of kV, enough to cause electrons accelerating across those potentials to emit x-rays when they smack into the positively charged surface.  Whatever is going on, it's a way to effectively concentrate the energy from mechanical work into displacing charges.  This is how Wimshurst machines and Van de Graaff generators work, even though we don't understand the microscopic physics of the charge generation and separation. There are disagreements to this day about the mechanisms at work in triboelectricity, including the role of adsorbates, surface chemistry, whether the charges transferred are electrons or ions, etc.  From how electronic charge transfer works between metals, or between metals and semiconductors, it's not crazy to imagine that somehow this should all come down to work functions or the equivalent.  Depending on the composition and structure of materials, the electrons in there can be bound more tightly (energetically deeper compared to the energy of an electron far away, also called "the vacuum" level) or more loosely (energetically shallower, closer to the energy of a free electron).  It's credible that bringing two such materials in contact could lead to electrons "falling down hill" from the more loosely-binding material into the more tightly binding one.   That clearly is not the whole story, though, or this would've been figured out long ago. This week, a new paper revealed an interesting wrinkle.  The net preference for picking up or losing charge seems to depend very clearly on the history of repeated contacts.  The authors used PDMS silicone rubber, and they find that repeated contacting can deterministically bake in a tendency for charge to flow one direction.  Using various surface spectroscopy methods, they find no obvious differences at the PDMS surface before/after the contacting procedures, but charge transfer is affected.   My sneaking suspicion is that adsorbates will turn out to play a huge role in all of this.  This may be one of those issues like friction (see here too), where there is a general emergent phenomenon (net charge transfer) that can take place via multiple different underlying pathways.  Experiments in ultrahigh vacuum with ultraclean surfaces will undoubtedly show quantitatively different results than experiments in ambient conditions, but they may both show triboelectricity.

The National Science Foundation was created 75 years ago, at the behest of Vannevar Bush, who put together the famed study, Science, The Endless Frontier, in 1945.  The NSF has played a critical role in a huge amount of science and engineering research since its inception, including advanced development of the laser, the page rank algorithm that ended up in google, and too many other contributions to list.   The NSF funds university research as well as some national facilities.  Organizationally, the NSF is an independent agency, meaning that it doesn’t reside under a particular cabinet secretary, though its Director is a presidential appointee who is confirmed by the US Senate.  The NSF comprises a number of directorates (most relevant for readers of this blog are probably Mathematical and Physical Sciences; Engineering;  and STEM Education, though there are several others).  Within the directorates are divisions (for example, MPS → Division of Materials Research; Division of Chemistry; Division of Physics; Division of Mathematics etc.).   Within each division are a variety of programs, spanning from individual investigator grants to medium to large center proposals, to group training grants, to individual graduate and postdoctoral fellowships.  Each program is administered by one or more program officers who are either scientists who have become civil servants, or "rotators", academics who take a leave of absence from their university positions to serve at the NSF for some number of years.  The NSF is the only agency whose mission historically has explicitly included science education.  The NSF's budget has been about $9B/yr (though until very recently there was supposedly bipartisan support for large increases), and 94% of its funds are spent on research, education, and related activities.  NSF funds more than 1/4 of all basic research done at universities in the US, and it also funds tech development, like small business innovation grants. The NSF, more than any other agency that funds physical science and engineering research, relies on peer review.  Grants are reviewed by individual reviewers and/or panels.  Compared to other agencies, the influence of program officers in the review process is minimal.  If a grant doesn't excite the reviewers, it won't get funded.  This has its pluses and minuses, but it's less of a personal networking process than other agencies.  The success rate for many NSF programs is low, averaging around 25% in DMR, and 15% or so for graduate fellowships.  Every NSF program officer with whom I've ever interacted has been dedicated and professional.   Well, yesterday the NSF laid off 11% of its workforce.  I had an exchange last night with a long-time NSF program director, who gave permission for me to share the gist, suitably anonymized.  (I also corrected typos.)  This person says that they want people to be aware of what's going on.  They say that NSF leadership is apparently helping with layoffs, and that "permanent Program Directors (feds such as myself) will be undergoing RIF or Reduction In Force process within the next month or so. So far, through buyout and firing today we lost about 16% of the workforce, and RIF is expected to bring it up to 50%."  When I asked further, this person said this was "fairly certain".   They went on:  "Another danger is budget.  We do no know what happens after the current CR [continuing resolution] ends March 14.  A long shutdown or another CR are possible.  For FY26 we are told about plans to reduce the NSF budget by 50%-75% - such reduction will mean no new awards for at least a year, elimination of divisions, merging of programs.  Individual researchers and professional societies can help by raising the voice of objection.  But realistically, we need to win the midterms to start real change.  For now we are losing this battle.  I can only promise you that NSF PDs are united as never before in our dedication to serve our communities of reesarchers and educators.  We will continue to do so as long as we are here."  On a related note, here is a thread by a just laid off NSF program officer.  Note that congress has historically ignored presidential budget requests to cut NSF, but it's not at all clear that this can be relied upon now.   Voluntarily hobbling the NSF is, in my view, a terrible mistake that will take decades to fix.  The argument that this is a fiscally responsible thing to do is weak.  The total federal budget expenditures in FY24 was $6.75T.  The NSF budget was $9B, or 0.13% of the total.  The secretary of defense today said that their plan is to cut 8% of the DOD budget every year for the next several years.  That's a reduction of 9 NSF budgets per year.   I fully recognize that many other things are going on in the world right now, and many agencies are under similar pressures, but I wanted to highlight the NSF in particular.  Acting like this is business as usual, the kind of thing that happens whenever there is a change of administration, is disingenuous.