Very busy time....

Sorry for the light blogging - between departmental duties and deadline-motivated writing, it's been very difficult to squeeze in much blogging.  Hopefully things will lighten up again in the next week or two.   In the meantime, I suggest watching old episodes of the excellent show Scrapheap Challenge (episode 1 here).  Please feel free to put in suggestions of future blogging topics in the comments below.  I'm thinking hard about doing a series on phases and phase transitions.

Max the Demon and the Entropy of Doom

My readers know I've complained/bemoaned repeatedly how challenging it can be to explain condensed matter physics on a popular level in an engaging way, even though that's the branch of physics that arguably has the greatest impact on our everyday lives.  Trying to take such concepts and reach an audience of children is an even greater, more ambitious task, and teenagers might be the toughest crowd of all.  A graphic novel or comic format is one visually appealing approach that is a lot less dry and perhaps more nonthreatening than straight prose.   Look at the success of xkcd and Randall Munroe!   The APS has had some reasonable success with their comics about their superhero Spectra.  Prior to that, Larry Gonick had done a very nice job on the survey side with the Cartoon Guide to Physics.  (On the parody side, I highly recommend Science Made Stupid (pdf) by Tom Weller, a key text from my teen years.  I especially liked Weller's description of the scientific method, and his fictional periodic table.)

Max the Demon and the Entropy of Doom is a new entry in the field, by Assa Auerbach and Richard Codor.  Prof. Auerbach is a well-known condensed matter theorist who usually writes more weighty tomes, and Mr. Codor is a professional cartoonist and illustrator.  The book is an entertaining explanation of the laws of thermodynamics, with a particular emphasis on the Second Law, using a humanoid alien, Max (the Demon), as an effective superhero.  

The comic does a good job, with nicely illustrated examples, of getting the point across about entropy as counting how many (microscopic) ways there are to do things.  One of Max's powers is the ability to see and track microstates (like the detailed arrangement and trajectory of every air molecule in this room), when mere mortals can only see macrostates (like the average density and temperature).    It also illustrates what we mean by temperature and heat with nice examples (and a not very subtle at all environmental message).   There's history (through the plot device of time travel), action, adventure, and a Bad Guy who is appropriately not nice (and has a connection to history that I was irrationally pleased about guessing before it was revealed).   My kids thought it was good, though my sense is that some aspects were too conceptually detailed for 12 years old and others were a bit too cute for world-weary 15.  Still, a definite good review from a tough crowd, and efforts like this should be applauded - overall I was very impressed.

Taxes and grad student tuition

As has happened periodically over the last couple of decades (I remember a scare about this when Newt Gingrich's folks ran Congress in the mid-1990s), a tax bill has been put forward in the US House that would treat graduate student tuition waivers like taxable income (roughly speaking).   This is discussed a little bit here, and here.

Here's an example of why this is an ill-informed idea.  Suppose a first-year STEM grad student comes to a US university, and they are supported by, say, departmental fellowship funds or a TA position during that first year.  Their stipend is something like $30K.  These days the university waives their graduate tuition - that is, they do not expect the student to pony up tuition funds.  At Rice, that tuition is around $45K.  Under the proposed legislation, the student would end up getting taxed as if their income was $75K, when their actual gross pay is $30K.   

That would be extremely bad for both graduate students and research universities.  Right off the bat this would create unintended (I presume) economic incentives, for grad students to drop out of their programs, and/or for universities to play funny games with what they say is graduate tuition.   

This has been pitched multiple times before, and my hypothesis is that it's put forward by congressional staffers who do not understand graduate school (and/or think that this is the same kind of tuition waiver as when a faculty member's child gets a vastly reduced tuition for attending the parent's employing university).  Because it is glaringly dumb, it has been fixed whenever it's come up before.  In the present environment, the prudent thing to do would be to exercise caution and let legislators know that this is a problem that needs to be fixed.

Links + coming soon

Real life is a bit busy right now, but I wanted to point out a couple of links and talk about what's coming up.

• I've been looking for ways to think about and discuss topological materials that might be more broadly accessible to non-experts, and I found this paper and videos like this one and this one.  Very cool, and I'm sorry I'd missed it back in '15 when it came out.
• In the experimental literature talking about realizations of Majorana fermions in the solid state, a key signature is a peak in the conductance at zero voltage - that's an indicator that there is a "zero-energy mode" in the system.  There are other ways to get zero-bias peaks, though, and nailing down whether this has the expected properties (magnitude, response to magnetic fields) has been a lingering issue.  This seems to nail down the situation more firmly.
• Discussions about "quantum supremacy" strictly in terms of how many qubits can be simulated on a classical computer right now seem a bit silly to me.  Ok, so IBM managed to simulate a handful of additional qubits (56 rather than 49).  It wouldn't shock me if they could get up to 58 - supercomputers are powerful and programmers can be very clever.  Are we going to get a flurry of news stories every time about how this somehow moves the goalposts for quantum computers?    
• I'm hoping to put out a review of Max the Demon and the Entropy of Doom, since I received my beautifully printed copies this past weekend.

Thoughts after a NSF panel

I just returned from a NSF proposal review panel.  I had written about NSF panels back in the early days of this blog here, back when I may have been snarkier.

• Some things have gotten better.  We can work from our own laptops, and I think we're finally to the point where everyone at these things is computer literate and can use the online review system.  The program officers do a good job making sure that the reviews get in on time (ahead of the meeting).
• Some things remain the same.  I'm still mystified at how few people from top-ranked programs (e.g., Harvard, Stanford, MIT, Cornell, Cal Tech, Berkeley) I see at these.  Maybe I just don't move in the right circles.  
• Best quote of the panel:  "When a review of one of my papers or proposals starts with 'Author says' rather than 'The author says', I know that the referee is Russian and I'm in trouble."
• Why does the new NSF headquarters have tighter security screenings that Reagan National Airport?  
• The growth of funding costs and eight years of numerically flat budgets has made this process more painful.  Sure looks like morale is not great at the agency.  Really not clear where this is all going to go over the next few years.  There was a lot of gallows humor about having "tax payer advocates" on panels.  (Everyone on the panel is a US taxpayer already, though apparently that doesn't count for anything because we are scientists.)
• NSF is still the most community-driven of the research agencies. 
• I cannot overstate the importance of younger scientists going to one of these and seeing how the system works, so you learn how proposals are evaluated.

Whither science blogging?

I read yesterday of the impending demise of scienceblogs, a site that has been around since late 2005 in one form or other.  I guess I shouldn't be surprised, since some of its bloggers have shifted to other sites in recent years, such as Ethan Siegel and Chad Orzel, who largely migrated to Forbes, and Rhett Allain, who went to Wired.  Steinn Sigurðsson is going back to his own hosted blog in the wake of this.

I hope this is just indicative of a poor business model at Seed Media, and not a further overall decline in blogging by scientists.  It's wonderful that online magazines like Quanta and Aeon and Nautilus are providing high quality, long-form science writing.  Still, I think everyone benefits when scientists themselves (in addition to professional science journalists) carve out some time to write about their fields.

Neutron stars and condensed matter physics

In the wake of the remarkable results reported earlier this week regarding colliding neutron stars, I wanted to write just a little bit about how a condensed matter physics concept is relevant to these seemingly exotic systems.

When you learn high school chemistry, you learn about atomic orbitals, and you learn that electrons "fill up" those orbitals starting with the lowest energy (most deeply bound) states, two electrons of opposite spin per orbital.  (This is a shorthand way of talking about a more detailed picture, involving words like "linear combination of Slater determinants", but that's a detail in this discussion.)  The Pauli principle, the idea that (because electrons are fermions) all the electrons can't just fall down into the lowest energy level, leads to this.  In solid state systems we can apply the same ideas.  In a metal like gold or copper, the density of electrons is high enough that the highest kinetic energy electrons are moving around at ~ 0.5% of the speed of light (!).  

If you heat up the electrons in a metal, they get more spread out in energy, with some occupying higher energy levels and some lower energy levels being empty.   To decide whether the metal is really "hot" or "cold", you need a point of comparison, and the energy scale gives you that.  If most of the low energy levels are still filled, the metal is cold.  If the ratio of the thermal energy scale, \(k_{\mathrm{B}}T\) to the depth of the lowest energy levels (essentially the Fermi energy, \(E_{\mathrm{F}}\) is much less than one, then the electrons are said to be "degenerate".  In common metals, \(E_{\mathrm{F}}\) is several eV, corresponding to a temperature of tens of thousands of Kelvin.  That means that even near the melting point of copper, the electrons are effectively very cold.

Believe it or not, a neutron star is a similar system.  If you squeeze a bit more than one solar mass into a sphere 10 km across, the gravitational attraction is so strong that the electrons and protons in the matter are crushed together to form a degenerate ball of neutrons.  Amazingly, by our reasoning above, the neutrons are actually very very cold.  The Fermi energy for those neutrons corresponds to a temperature of nearly \(10^{12}\) K.  So, right up until they smashed into each other, those two neutron stars spotted by the LIGO observations were actually incredibly cold, condensed objects.   It's also worth noting that the properties of neutron stars are likely affected by another condensed matter phenomenon, superfluidity.   Just as electrons can pair up and condense into a superconducting state under some circumstances, it is thought that cold, degenerate neutrons can do the same thing, even when "cold" here might mean \(5 \times 10^{8}\) K.

Gravitational waves again - should be exciting

There is going to be a big press conference tomorrow, apparently to announce that LIGO/VIRGO has seen an event (binary neutron star collision) directly associated with a gamma ray burst in NGC 4993.  Fun stuff, and apparently the worst-kept secret in science right now.  This may seem off-topic for a condensed matter blog, but there's physics in there which isn't broadly appreciated, and I'll write a bit about it after the announcement.

Piezo controller question - followup.

A couple of weeks ago I posted:

Anyone out there using a Newport NPC3SG controller to drive a piezo positioning stage, with computer communication successfully talking to the NPC3SG?  If so, please leave a comment so that we can get in touch, as I have questions.

No responses so far.  This is actually the same unit as this thing:
https://www.piezosystem.com/products/piezo_controller/piezo_controller_3_channel_version/nv_403_cle/

In our unit from Newport, communications simply don't work properly.  Timeout problems.  The labview code supplied by Newport (the same code paired with the link above) has these problems, as do many other ways of trying to talk with the instrument.  Has anyone out there had success in using a computer to control and read this thing?   At issue is whether this is a hardware problem with our unit, or whether there is a general problem with these.  The vendor has been verrrrrrrrry slow to figure this out.

The Abnormal Force

How does the chair actually hold you up when you sit down?  What is keeping your car tires from sinking through the road surface?  What is keeping my coffee mug from falling through my desk?  In high school and first-year undergrad physics, we teach people about the normal force - that is a force that acts normal (perpendicular) to a surface, and it takes on whatever value is needed so that solid objects don't pass through each other.

The microscopic explanation of the normal force is that the electrons in the atoms of my coffee mug (etc.) interact with the electrons in the atoms of the desk surface, through a combination of electrostatics (electrons repel each other) and quantum statistics (the Pauli principle means that you can't just shuffle electrons around willy-nilly).  The normal force is "phenomenological" shorthand.  We take the observation that solid objects don't pass through each other, deduce that whatever is happening microscopically, the effect is that there is some force normal to surfaces that touch each other, and go from there, rather than trying to teach high school students how to calculate it from first principles.  The normal force is an emergent effect that makes sense on macroscopic scales without knowing the details.  This is just like how we teach high school students about pressure as a useful macroscopic concept, without actually doing a statistical calculation of the average perpendicular force per area on a surface due to collisions with molecules of a gas or a liquid.  

You can actually estimate the maximum reasonable normal force per unit area.  If you tried to squeeze the electrons of two adjacent atoms into the volume occupied by one atom, even without the repulsion of like charges adding to the cost, the Pauli principle means you'd have to kick some of those electrons into higher energy levels.  If a typical energy scale for doing that for each electron was something like 1 eV, and you had a few electrons per atom, and the areal density of atoms is around 10¹⁴ per cm², then we can find the average force \(F_{\mathrm{av}}\) required to make a 1 cm² area of two surfaces overlap with each other.   We'd have \(F_{\mathrm{av}} d \sim 10^{15}\)eV, where \(d\) is the thickness of an atom, around 0.3 nm.   That's around 534000 Newtons/cm², or around 5.3 GPa.   That's above almost all of the yield stresses for materials (usually worrying about tension rather than compression) - that just means that the atoms themselves will move around before you really push electrons around.

Very occasionally, when two surfaces are brought together, there is a force that arises at the interface that is not along the normal direction.  A great example of that is in this video, which shows two graphite surfaces that spontaneously slide in the plane so that they are crystallographically aligned.  That work comes from this paper.

As far as I can tell, there is no official terminology for such a spontaneous in-plane force.  In the spirit of one of my professional heroes David Mermin, who coined the scientific term boojum, I would like to suggest that such a transverse force be known as the abnormal force.  (Since I don't actually work in this area and I'm not trying to name the effect after myself, hopefully the barrier to adoption will be lower than the one faced by Mermin, who actually worked on boojums :-)  ).

Gravitational radiation for the win + communicating science

As expected, LIGO was recognized by the Nobel Prize in physics this year.  The LIGO experiment is an enormous undertaking that combines elegant, simple theoretical ideas; incredible engineering and experimental capabilities; and technically virtuosic numerical theoretical calculations and data analysis techniques.  It's truly a triumph.

I did think it was interesting when Natalie Wolchover, one of the top science writers out there today, tweeted:   Thrilled they won, thrilled not to spend this morning speed-reading about some bizarre condensed matter phenomenon.

This sentiment was seconded by Peter Woit, who said he thought she spoke for all science journalists.

Friendly kidding aside, I do want to help.  Somehow it's viewed as comparatively easy and simple to write about this, or this, or this, but condensed matter is considered "bizarre".  

Gravitational radiation redux + Nobel speculation

This past week, there was exciting news that the two LIGO detectors and the VIRGO interferometer had simultaneously detected the same event, a merger of black holes estimated to have taken place 1.6 billion lightyears away.  From modeling the data, the black hole masses are estimated at around 25 and 30 solar masses, and around 2.7 solar masses worth of energy (!) was converted in the merger into gravitational radiation.  The preprint of the paper is here.  Check out figure 1.  With just the VIRGO data, the event looks really marginal - by eye you would be hard pressed to pick it out of the fluctuating detector output.  However, when that data is thrown into the mix with that from the (completely independent from VIRGO) detectors, the case is quite strong.

This is noteworthy for (at least) two reasons.  First, there has been some discussion about the solidity of the previously reported LIGO results - this paper (see here for a critique of relevant science journalism) argues that there are some surprising correlations in the noise background of the two detectors that could make you wonder about the analysis.  After all, the whole point of having two detectors is that a real event should be seen by both, while one might reasonably expect background jitter to be independent since the detectors are thousands of miles apart.  Having a completely independent additional detector in the mix should be useful in quantifying any issues.  Second, having the additional detector helps nail down the spot in the sky where the gravitational waves appear to originate.  This image shows how previous detections could only be localized by two detectors to a band spanning lots of the sky, while this event can be localized down to a spot spanning a tenth as much solid angle.    This is key to turning gravitational wave detectors into serious astronomy tools, by trying to link gravitational event detection to observations across the electromagnetic spectrum.  There were rumors, for example, that LIGO had detected what was probably a neutron star collision (smaller masses, but far closer to earth), the kind of event thought to produce dramatic electromagnetic signatures like gamma ray bursts.

On that note, I realized Friday that this coming Tuesday is the announcement of the 2017 Nobel in physics.  Snuck up on me this time.  Speculate away in the comments.  Since topology in condensed matter was last year's award, it seems likely that this year will not be condensed matter-related (hurting the chances of people like Steglich and Hosono for heavy fermion and iron superconductors, respectively).  Negative index phenomena might be too condensed matter related.   The passing last year of Vera Rubin and Debra Jin is keenly felt, and makes it seem less likely that galactic rotation curves (as evidence for dark matter) or ultracold fermions would get it this year.  Bell's inequality tests (Aspect, Zeilinger, Clauser) could be there.   The LIGO/VIRGO combined detection happened too late in the year to affect the chances of this being the year for gravitational radiation (which seems a shoe-in soon).

The terahertz gap

https://commons.wikimedia.org/wiki/File:Thz_freq_in_EM_spectrum.png?uselang=en-gb

At a thesis proposal talk yesterday, I realized that I hadn't ever written anything specifically about terahertz radiation (THz, or if you're trying to market something, t-rays).   Terahertz (10¹² Hz) is the frequency of electromagnetic radiation higher than microwaves, but lower than what is traditionally labeled the far infrared.  Sometimes called "mm wave" radiation (1 THz would be a free-space wavelength of about 0.3 mm or 300 microns), THz is potentially very useful for communications (pdf, from here), imaging (here, here, here), and range detection (see here for an impressive google project; or here for an article about THz for self-driving cars), among other things.  It's also right around the frequency range of a lot of vibrations in molecules and solids, so it can be used for spectroscopy, though it's also around the energy range where water vapor in the atmosphere can be an efficient absorber.

This frequency region is an awkward middle ground, however.  That's sometimes why it's referred to as the "terahertz gap".

We tend to produce electromagnetic radiation by one of two approaches.  Classically, accelerating charges radiate electromagnetic waves.  In the low frequency limit, there are various ways to generate voltages that oscillate - we can in turn use those to drive oscillating currents and thus generate radio waves, for example.  See here for a very old school discussion.  It is not trivial to shake charges back and forth at THz frequencies, however.  It can be done, but it's very challenging.  One approach to generating a pulse of THz radiation is to use a photoconductive antenna.  Take two electrodes close together on a semiconductor substrate, with a voltage applied between them.  Smack the semiconductor with an ultrafast optical pulse that has a frequency high enough to photoexcite a bunch of charge carriers - those then accelerate from the electric field between the electrodes and emit a pulse of radiation, including THz frequencies.

The other limit we often take in generating light is to work with some quantum system that has a difference in energy levels that is the same energy as the photons we want to generate.  This is the limit of atomic emission (say, having an electron drop from the 2p orbital to the 1s orbital of a hydrogen atom, and emitting an ultraviolet photon of energy around 10 eV) and also the way many solid state devices work (say, having an electron drop from the bottom of the conduction band to the top of the valence band in InGaAsP to produce a red photon of energy around 1.6 eV in a red LED).  The problem with this approach for THz is that the energy scale in question is very small - 1 THz is about 4 milli-electron volts (!).  As far as I know, there aren't naturally occurring solids with energy level splittings that small, so the approach from this direction has been to create artificial systems with such electronic energy gaps - see here.   (Ironically, there are some molecular systems with transitions considerably lower in energy than the THz that can be used to generate microwaves, as in this famous example.)

It looks like THz is starting to take off for technologies, particularly as more devices are being developed for its generation and detection.  SiGe-based transistors, for example, can operate at very high intrinsic speeds, and like in the thesis proposal I heard yesterday, these devices are readily made now and can be integrated into custom chips for exactly the generation and detection of radiation approaching a terahertz.  Exciting times.

Lab question - Newport NPC3SG

Anyone out there using a Newport NPC3SG controller to drive a piezo positioning stage, with computer communication successfully talking to the NPC3SG?  If so, please leave a comment so that we can get in touch, as I have questions.

Faculty position at Rice - theoretical astro-particle/cosmology

Assistant Professor Position at Rice University in

Theoretical Astro-Particle Physics/Cosmology

The Department of Physics and Astronomy at Rice University in Houston, Texas, invites applications for a tenure-track faculty position (Assistant Professor level) in Theoretical Astro-Particle physics and/or Cosmology. The department seeks an outstanding individual whose research will complement and connect existing activities in Nuclear/Particle physics and Astrophysics groups at Rice University (see http://physics.rice.edu). This is the second position in a Cosmic Frontier effort that may eventually grow to three members. The successful applicant will be expected to develop an independent and vigorous research program, and teach graduate and undergraduate courses. A PhD in Physics, Astrophysics or related field is required.

Applicants should send the following: (i) cover letter; (ii) curriculum vitae (including electronic links to 2 relevant publications); (iii) research statement (4 pages or less); (iv) teaching statement (2 pages or less); and (v) the names, professional affiliations, and email addresses of three references.  To apply, please visit: http://jobs.rice.edu/postings/11772.  Applications will be accepted until the position is filled, but only those received by Dec 15, 2017 will be assured full consideration. The appointment is expected to start in July 2018.  Further inquiries should be directed to the chair of the search committee, Prof. Paul Padley (padley@rice.edu).

Rice University is an Equal Opportunity Employer with commitment to diversity at all levels, and considers for employment qualified applicants without regard to race, color, religion, age, sex, sexual orientation, gender identity, national or ethnic origin, genetic information, disability or protected veteran status.

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Faculty position at Rice - experimental condensed matter

Faculty Position in Experimental Condensed Matter Physics Rice University

The Department of Physics and Astronomy at Rice University in Houston, TX invites applications for a tenure-track faculty position in experimental condensed matter physics.  The department expects to make an appointment at the assistant professor level. This search seeks an outstanding individual whose research interest is in hard condensed matter systems, who will complement and extend existing experimental and theoretical activities in condensed matter physics on semiconductor and nanoscale structures, strongly correlated systems, topological matter, and related quantum materials (see http://physics.rice.edu/). A PhD in physics or related field is required. 

Applicants to this search should submit the following: (1) cover letter; (2) curriculum vitae; (3) research statement; (4) teaching statement; and (5) the names, professional affiliations, and email addresses of three references. For full details and to apply, please visit: http://jobs.rice.edu/postings/11782. Applications will be accepted until the position is filled. The review of applications will begin October 15 2017, but all those received by December 1 2017 will be assured full consideration. The appointment is expected to start in July 2018.  Further inquiries should be directed to the chair of the search committee, Prof. Emilia Morosan (emorosan@rice.edu).  

Rice University is an Equal Opportunity Employer with commitment to diversity at all levels, and considers for employment qualified applicants without regard to race, color, religion, age, sex, sexual orientation, gender identity, national or ethnic origin, genetic information, disability or protected veteran status.

DOE experimental condensed matter physics PI meeting, day 3

And from the last half-day of the meeting:

• Because the mobile electrons in graphene have an energy-momentum relationship similar to that of relativistic particles, the physics of electrons bound to atomic-scale defects in graphene has much in common with the physics that sets the limits on the stability of heavy atoms - when the kinetic energy of the electrons in the innermost orbitals is high enough that relativistic effects become very important.  It is possible to examine single defect sites with a scanning tunneling microscope and look at the energies of bound states, and see this kind of physics in 2d.  
• There is a ton of activity concentrating on realizing Majorana fermions, expected to show up in the solid state when topologically interesting "edge states" are coupled to superconducting leads.  One way to do this would be to use the edge states of the quantum Hall effect, but usually the magnetic fields required to get in the quantum Hall regime don't play well with superconductivity.  Graphene can provide a way around this, with amorphous MoRe acting as very efficient superconducting contact material.  The results are some rather spectacular and complex superconducting devices (here and here).
• With an excellent transmission electron microscope, it's possible to carve out atomically well defined holes in boron nitride monolayers, and then use those to create confined potential wells for carriers in graphene.  Words don't do justice to the fabrication process - it's amazing.  See here and here.
• It's possible to induce and see big collective motions of a whole array of molecules on a surface that each act like little rotors.
• In part due to the peculiar band structure of some topologically interesting materials, they can have truly remarkable nonlinear optical properties.

My apologies for not including everything - side discussions made it tough to take notes on everything, and the selection in these postings is set by that and not any judgment of excitement.  Likewise, the posters at the meeting were very informative, but I did not take notes on those.

DOE experimental condensed matter PI meeting, day 2

More things I learned:

• I've talked about skyrmions before.  It turns out that by coupling a ferromagnet to a strong spin-orbit coupling metal, one can stabilize skyrmions at room temperature.  They can be visualized using magnetic transmission x-ray microscopy - focused, circularly polarized x-ray studies.   The skyrmion motion can show its own form of the Hall effect.  Moreover, it is possible to create structures where skyrmions can be created one at a time on demand, and moved back and forth in a strip of that material - analogous to a racetrack memory.
• Patterned arrays of little magnetic islands continue to be a playground for looking at analogs of complicated magnetic systems.  They're a kind of magnetic metamaterial.  See here.  It's possible to build in frustration, and to look at how topologically protected magnetic excitations (rather like skyrmions) stick around and can't relax.
• Topological insulator materials, with their large spin-orbit effects and surface spin-momentum locking, can be used to pump spin and flip magnets.  However, the electronic structure of both the magnet and the TI are changed when one is deposited on the other, due in part to interfacial charge transfer.
• There continues to be remarkable progress on the growth and understanding of complex oxide heterostructures and interfaces - too many examples and things to describe.
• The use of nonlinear optics to reveal complicated internal symmetries (talked about here) continues to be very cool.
• Antiferromagnetic layers can be surprisingly good at passing spin currents.  Also, I want to start working on yttrium iron garnet, so that I can use this at some point in a talk.
• It's possible to do some impressive manipulation of the valley degree of freedom in 2d transition metal dichalcogenides, creating blobs of complete valley polarization, for example.  It's possible to use an electric field to break inversion symmetry in bilayers and turn some of these effects on and off electrically.
• The halide perovskites actually can make fantastic nanocrystals in terms of optical properties and homogeneity.

DOE experimental condensed matter PI meeting, day 1

I'm pressed for time, so this is brief, but here are some things I learned yesterday:

• An electric field perpendicular to the plane can split and shift the Landau levels of bilayer graphene.  See here.
• The quantum Hall effect in graphene and other 2d systems still has a lot of richness and life in it.
• I have one word for you...."polaritons".
• It's possible to set up a tunneling experiment, from one "probe" 2d electron gas that has a small, tight Fermi surface, into a "sample" 2d electron gas of interest.  By playing with the in-plane magnetic field, the tunneling electrons can pick up momentum in the plane as they tunnel.  The result is, the tunneling current as a function of voltage and transverse fields lets you map out exactly the "sample" electronic states as a function of energy and momentum, like ARPES without the PES part.  See here.
• Squeezing mechanically to apply pressure can actually produce dramatic changes (quantum phase transitions) in unusual fractional quantum Hall states.
• How superconductivity dies in the presence of disorder, magnetic field, and temperature remains very rich and interesting.  The "Bose metal", when magnetic field kills global phase coherence without completely ripping apart Cooper pairs, can be an important part of that transition.  For related work, see here.
• One should be very careful in interpreting ARPES data.  It's entirely possible that not everything identified as some exotic topological material really fits the bill - see here.  On the other hand, sometimes you do see real topologically interesting band structure.
• The DOE still has laptops running Windows XP.

DOE Experimental Condensed Matter PI meeting, 2017

The Basic Energy Sciences program is part of the US Department of Energy's Office of Science, and they are responsible for a lot of excellent science research funding.  The various research areas within BES have investigator meetings every two years, and at the beginning of this coming week is the 2017 PI meeting for the experimental condensed matter physics program.  As I've done in past years,  I will try to write up a bulleted list of things I learn.   (See here, here, and here for the 2013 meeting; see here, here, here, and here for the 2015 meeting).

Good luck and stay safe to those in Florida about to get hit by Hurricane Irma.  It's very different than Harvey (much more of a concern about wind damage and storm surge, much less about total rainfall), but still very dangerous.

Lastly, Amazon seems to have my book available for a surprisingly low price right now ($62, though the list is $85).  I (and my publisher) still have no idea how they can do this without losing money.