Thursday, March 07, 2024

APS March Meeting 2024, Day 4 and wrap-up

Because of the timing of my flight back to Houston, I really only went to one session today, in which my student spoke as did some collaborators.  It was a pretty interesting collection of contributed talks.  

  • The work that's been done on spin transport in multiferroic insulators is particularly interesting to me.  A relevant preprint is this one, in which electric fields are used to reorient \(\mathbf{P}\) in BiFeO3, which correspondingly switches the magnetization in this system (which is described by a complicated spin cycloid order) and therefore modulates the transmission of spin currents (as seen in ferromagnetic resonance).  
  • Similarly adding a bit of La to BiFeO3 to favor single ferroelectric domain formation was a neat complement to this.
  • There were also multiple talks showing the utility of the spin Hall magnetoresistance as a way to characterize spin transport between magnetic insulators and strong spin-orbit coupled metals.
Some wrap-up thoughts:
  • This meeting venue and environment was superior in essentially every way relative to last year's mess in Las Vegas.  Nice facilities, broadly good rooms, room sizes, projectors, and climate control.  Lots of hotels.  Lots of restaurants that are not absurdly expensive.  I'd be very happy to have the meeting in Minneapolis again at some point.  There was even a puppy-visiting booth at the exhibit hall on Tuesday and Thursday.
  • Speaking of the exhibit hall, I think this is the first time I've been at a meeting where a vendor was actually running a dilution refrigerator on the premises.  
  • Only one room that I was in had what I would describe as a bad projector (poor color balance, loud fan, not really able to be focused crisply).  I also did not see any session chair this year blow it by allowing speakers to blow past their allotted times.
  • We really lucked out on the weather.  
  • Does anyone know what happens if someone ignores the "Warning: Do Not Drive Over Plate" label on the 30 cm by 40 cm yellow floor plate in the main lobby?  Like, does it trigger a self-destruct mechanism, or the apocalypse or something?
  • Next year's combined March/April meeting in Anaheim should be interesting - hopefully the venue is up to the task, and likewise I hope there are good, close housing and food options.

Wednesday, March 06, 2024

APS March Meeting 2024, Day 3

My highlights today are a bit thin, because I was fortunate enough to spend time catching up with collaborators and old friends, but here goes:
  • Pedram Roushan from Google gave an interesting talk about noisy intermediate-scale quantum experiments for simulation.  He showed some impressive data looking at the propagation of (simulated) magnons in the 1D Heisenberg spin chain.
  • In the same session, Lieven Vandersypen from Delft presented their recent results using gate-defined Ge/SiGe quantum dot arrays to simulate a small-scale version of the Hubbard model.  Looking at exciton formation and propagation in a Hubbard ladder while being able to tune many parameters, the data are pretty neat, though I have to say it seems like scaling this up to large arrays will be extremely challenging in terms of layout and tuning.  He also showed some in-preparation work on spin propagation in similar arrays - neat.
  • In a completely different session, Jacques Prost, recipient of this year's Onsager Prize, gave an interesting talk about broken symmetries and dynamics of living tissue.  This included cell motion driven by nematicity (living tissue as liquid crystal....) and how in a cylindrical environment this can lead to rotation of growing tissue.  These sorts of interactions in "active matter" can be related to how tissue grows and differentiates in living systems.
  • My colleague Gustavo Scuseria is this year's recipient of the Aneesha Rahman Prize, and he gave a good explanation of his group's recent work on using dualities to map strongly correlated models onto more tractable (polynomial-growth rather than exponential growth in problem size) equivalent weakly correlated models.
  • In a session on quantum spin liquids, Tyrel McQueen of Johns Hopkins spoke about two examples of his group's recent work.  Chemical substitution can help tune interactions in a Kitaev spin liquid candidate, and they've also examined the controlled interplay of charge density waves and magnetic order.  The talk did a great job of conveying a taste of the breadth and depth of the space of quantum magnets.
  • Lastly, Chih-Yuan Lu, recipient of this year's George E. Pake Prize, gave a very nice historical overview of the development of semiconductor electronics from the integrated circuit to the present frontiers (of gate-all-around transistors and 3D integrated NAND memory).
Two other notes not directly germane to the APS meeting:
  • The AAAS appropriations tracker shows how outlays for the coming year are shaping up for NSF and the other agencies.  </begin rant>Can someone explain to me why the conference NSF budget allocation for research ends up -8.5%, when the House pushed +0.3% and the Senate pushed -2.9%? Also, cutting the STEM education budget (which includes GRFP) by 28% seems terrible.  Griping about US STEM competitiveness and the need for developing the next-generation technical workforce, while simultaneously cutting research training resources:  Congress in action.   Once again, they feel good about supporting the authorization of doubling the NSF budget over five years, but don't actually want to appropriate the funds to do it.  </end rant>
  • Purely by random chance (ahem), I want to point to this column.

Tuesday, March 05, 2024

APS March Meeting 2024, Day 2

A decent part of today was spent in conversation with friends and colleagues, but here are some high points of scientific talks:

More tomorrow....

Monday, March 04, 2024

APS March Meeting 2024, Day 1

There is no question that the meeting venue in Minneapolis is superior in multiple ways to last year's meeting in Las Vegas.  The convention center doesn't feel scarily confining, and it also doesn't smell like a combination of cigarettes and desperation.

Here are a few highlights from the day:

  • There was an interesting session about "polar materials", systems that have the same kind of broken inversion symmetry within a unit cell as ferroelectrics; this includes "polar metals" which host mobile charge carriers.  One polar material family involving multiferroic insulators was presented by Daniel Flavián, in which dielectric (capacitance) measurements can show magnetic quantum critical phenomena, as in here and here.  Both sets of materials examined, Rb2Cu2Mo3O12 and Cs2Cu2Mo3O12, show remarkable dielectric effects due to fluctuating electric dipoles, connected to quantum critical points at B-field driven transitions between magnetic ordered states.
  • Natalia Drichko from Johns Hopkins showed Raman spectroscopy data on an organic Mott insulator, in which melting charge order is connected to spin fluctuations.
  • Pavel Volkov from U Conn discussed doped strontium titanate (STO), an example of an incipient polar metal, and looking at how polar fluctuations might be connected with the mechanism behind the unusual superconductivity of STO. 
  • The last talk of that session that I saw was Pablo Jarillo-Herrero giving a characteristically clear presentation about sliding ferroelectricity.  Taking a material like hBN and trying to stack a bilayer with perfect A-A alignment is not energetically favored - it's lower in energy if the two layers shift relative to each other by a third of a lattice parameter, resulting in an out-of-plane electric dipole moment, pointing either up or down depending on the direction of the shift.  Applying a sufficiently large electric field perpendicular to the plane can switch the system - this works on TMDs as well.  Putting a moire bilayer in the mix, and you can get some neat charge ratcheting effects
  • The session on transport in non-Fermi liquids was fun and informative.  I thought the discussion of possible intrinsic nonlinear transport in strange metals was intriguing.
  • I also saw a couple of interesting invited talks (here and here) about experiments that try to use electronic transport in adjacent layers to probe nontrivial magnetic properties of adjacent spin ices.  Very cool.
More tomorrow....

Sunday, March 03, 2024

APS March Meeting 2024 - coming soon

This week I'm going to be at the APS March Meeting in Minneapolis.  As I've done in past years, I will try to write up some highlights of talks that I am able to see, though it may be hit-or-miss.  If readers have suggestions for sessions or talks that they think will be particularly interesting, please put them in the comments.

Sunday, February 25, 2024

2024 version: Advice on choosing a graduate school

It's been four years since I posted the previous version of this, so it feels like the time is right for an update.

This is written on the assumption that you have already decided, after careful consideration, that you want to get an advanced degree (in physics, though much of this applies to any other science or engineering discipline).  This might mean that you are thinking about going into academia, or it might mean that you realize such a degree will help prepare you for a higher paying technical job outside academia.  Either way,  I'm not trying to argue the merits of a graduate degree - let's take it as given that this is what you want to do.

  • It's ok at the applicant stage not to know exactly what research area you want to be your focus.  While some prospective grad students are completely sure of their interests, that's more the exception than the rule.  I do think it's good to have narrowed things down a bit, though.  If a school asks for your area of interest from among some palette of choices, try to pick one (rather than going with "undecided").  We all know that this represents a best estimate, not a rigid commitment.
  • If you get the opportunity to visit a school, you should go.  A visit gives you a chance to see a place, get a subconscious sense of the environment (a "gut" reaction), and most importantly, an opportunity to talk to current graduate students.  Always talk to current graduate students if you get the chance - they're the ones who really know the score.  A professor should always be able to make their work sound interesting, but grad students can tell you what a place is really like.
  • International students may have a very challenging time being able to visit schools in the US, between the expense (many schools can help defray costs a little but cannot afford to pay for airfare for trans-oceanic travel) and visa challenges.  Trying to arrange zoom discussions with people at the school is a possibility, but that can also be challenging.  I understand that this constraint tends to push international students toward making decisions based heavily on reputation rather than up-close information.  
  • Picking an advisor and thesis area are major decisions, but it's important to realize that those decisions do not define you for the whole rest of your career.  I would guess (and if someone had real numbers on this, please post a comment) that the very large majority of science and engineering PhDs end up spending most of their careers working on topics and problems distinct from their theses.  Your eventual employer is most likely going to be paying for your ability to think critically, structure big problems into manageable smaller ones, and knowing how to do research, rather than the particular detailed technical knowledge from your doctoral thesis.  A personal anecdote:  I did my graduate work on the ultralow temperature properties of amorphous insulators.  I no longer work at ultralow temperatures, and I don't study glasses either; nonetheless, I learned a huge amount in grad school about the process of research that I apply all the time.
  • Always go someplace where there is more than one faculty member with whom you might want to work.  Even if you are 100% certain that you want to work with Prof. Smith, and that the feeling is mutual, you never know what could happen, in terms of money, circumstances, etc.  Moreover, in grad school you will learn a lot from your fellow students and other faculty.  An institution with many interesting things happening will be a more stimulating intellectual environment, and that's not a small issue.
  • You should not go to grad school because you're not sure what else to do with yourself.  You should not go into research if you will only be satisfied by a Nobel Prize.  In both of those cases, you are likely to be unhappy during grad school.  
  • I know grad student stipends are low, believe me.  However, it's a bad idea to make a grad school decision based purely on a financial difference of a few hundred or a thousand dollars a year.  Different places have vastly different costs of living - look into this.  Stanford's stipends are profoundly affected by the cost of housing near Palo Alto and are not an expression of generosity.  Pick a place for the right reasons.
  • Likewise, while everyone wants a pleasant environment, picking a grad school largely based on the weather is silly.  
  • Pursue external fellowships if given the opportunity.  It's always nice to have your own money and not be tied strongly to the funding constraints of the faculty, if possible.  (It's been brought to my attention that at some public institutions the kind of health insurance you get can be complicated by such fellowships.  In general, I still think fellowships are very good if you can get them.)
  • Be mindful of how departments and programs are run.  Is the program well organized?  What is a reasonable timetable for progress?  How are advisors selected, and when does that happen?  Who sets the stipends?  What are TA duties and expectations like?  Are there qualifying exams?  Where have graduates of that department gone after the degree?  Are external internships possible/unusual/routine? Know what you're getting into!  Very often, information like this is available now in downloadable graduate program handbooks linked from program webpages.   
  • When talking with a potential advisor, it's good to find out where their previous students have gone and how long a degree typically takes in their group.  What is their work style and expectations?   How is the group structured, in terms of balancing between team work to accomplish goals vs. students having individual projects over which they can have some ownership? 
  • Some advice on what faculty look for in grad students:  Be organized and on-time with things.  Be someone who completes projects (as opposed to getting most of the way there and wanting to move on).  Doctoral research should be a collaboration.  If your advisor suggests trying something and it doesn't work (shocking how that happens sometimes), rather than just coming to group meeting and saying "It didn't work", it's much better all around to be able to say "It didn't work, but I think we should try this instead", or "It didn't work, but I think I might know why", even if you're not sure. 
  • It's fine to try to communicate with professors at all stages of the process.  We'd much rather have you ask questions than the alternative.  If you don't get a quick response to an email, it's almost certainly due to busy-ness, and not a deeply meaningful decision by the faculty member.  For a sense of perspective: I get 50+ emails per day of various kinds not counting all the obvious spam that gets filtered.  

There is no question that far more information is now available to would-be graduate students than at any time in the past.  Use it.  Look at departmental web pages, look at individual faculty member web pages.  Make an informed decision.  Good luck!

Tuesday, February 13, 2024

Continuing Studies course, take 2

A year and a half ago, I mentioned that I was going to teach a course through Rice's Glasscock School of Continuing Studies, trying to give a general audience introduction to some central ideas in condensed matter physics.  Starting in mid-March, I'm doing this again.  Here is a link to the course registration for this synchronous online class.  This course is also intended as a potential continuing education/professional development offering for high school teachers, community college instructors, and other educators, and thanks to the generous support of the NSF, the Glasscock School is able to offer a limited number of full scholarships for educators - apply here by February 27 for consideration.   

(I am aware that the cost of the course is not trivial; at some point in the future I will make the course materials available broadly, and I will be sure to call attention to that at the time.)