## Tuesday, March 21, 2023

### What do we want in a conference venue?

The APS March Meeting was in Las Vegas this year, and I have yet to talk to a single attendee who liked that decision in hindsight.  In brief, the conference venue seemed about 10% too small (severe crowding issues in hallways between sessions); while the APS deal on hotels was pretty good, they should have prominently warned people that not using the APS housing portal means you fall prey to Las Vegas’s marketing schtick of quoting a low room rate but hiding large “resort fees”; with the exception of In N Out Burger, the food was very overpriced (e.g. $12 for a coffee and a muffin in the Starbucks in my hotel); and indoor spaces in town generally smelled like stale cigarettes, ineffective carpet cleaner, and desperation. I don’t think it’s that hard to enumerate what most people would like out of a conference venue, if we are intending to have in-person meetings and are going to spend grant money and valuable time to attend the meeting with our groups. (I’m taking as a given that the March meeting is large - now up to 12K attendees, for good or ill - and I know that’s so big that some people will decide that it’s too unwieldy to be worth going. Likewise, I know that the logistics are always difficult in terms of the abstract sorting and trying to make sure that likely-popular sessions get higher capacity rooms.) Off the top of my head, I would like: • A meeting venue that can accommodate everyone without feeling dangerously crowded at high volume transit times between sessions, with a good selection of hotels nearby that don’t have crazy room rates. (I know that the meeting growth already likely rules out a lot of places that have hosted the March meeting in the past.) • A high density of relatively cheap restaurants, including sandwich places, close to the venue for lunch, so that a quick bite is possible without hiking a mile or being forced to spend$20 on convention center food.
• Actual places to sit (tables and chairs) to talk with fellow attendees.  Las Vegas had a much smaller number of these (indoors) than previous locations.
• Reasonable availability of water (much better these days than in the past) and not-outrageously-priced coffee and tea.
• Wifi that actually can accommodate the number of attendees; at some point in Las Vegas I basically gave up on the conference wifi and tethered to my phone.  Remember, many of us still have to get some level of work done (like submitting annoyingly timed proposals) while at these.
• Modern levels of accommodations for nursing mothers, childcare, facilities for those with disabilities or mobility issues, etc.
Are there major items that I’m missing?  Do readers have suggestions for meeting sites that can hit all of these?  I am well aware that the APS is financially constrained to make these arrangements years in advance.  It can’t hurt to discuss this, though, especially raising concerns about problems to avoid.

## Thursday, March 16, 2023

### Recent RT superconductivity claim - summary page

In the interests of saving people from lots of googling or scrolling through 170+ comments, here is a bulleted summary of links relevant to the recent claim of room temperature superconductivity in a nitrogen-doped lutetium hydride compound under pressure.
• Dias's contributed talk at the APS meeting is here on youtube.
• Here is the promotional video put out by Rochester as part of the media release.  It odd to me that the department chair and the dean of the PI are both in this video.
• Here is the pubpeer page that has sprung up with people reporting concerns about the paper.
• The comments attached to the paper itself contain interesting discussion (though strangely an informed comment from Julia Deitz about the EDX data was repeatedly deleted as "spam")
• There was a lot of media coverage of this paper.  The Wall Street Journal was comparatively positive.  The New York Times was more nuanced.  Quanta had a thorough article with a witty headline describing the controversy surrounding the claim.  The APS had an initial brief news report and a more extensive article emphasizing the concerns about the paper.
• Experimental preprints have appeared looking at this.  The first observes a color change under pressure in LuH2, but no superconductivity in that related compound.  The second is a direct replication attempt, finding x-ray structural data matching the report but no superconductivity in that material up to higher pressures and down to 10 K.  Note that another preprint appeared last week reporting superconductivity at about 71 K in a different lutetium hydride at much higher pressures.
• A relevant and insightful talk from James Hamlin is here, from a recent online workshop about reproducibility in condensed matter physics.  Note that (as reported in this twitter thread) significant portions of Hamlin's doctoral thesis appear verbatim in Dias' thesis.
No doubt there are more; please let me know if there are additional key links that I've missed (not every twitter comment is important).

## Friday, March 10, 2023

### APS March Meeting 2023, Day 4 + wrapup

My last day at the March Meeting was a bit scattershot, but here are a few highlights:

• In a session about spin transport, the opening invited talk by Jiaming He was a clear discussion of recent experimental results on spin Seebeck effects in the magnetic insulator LuFeO3. The system is quite complicated because the net magnetization direction depends nontrivially on the external field, leading to spin transport signatures with a complicated field orientation relationship.
• There was an invited session about 2D magnets, and Roland Kawakami gave a clear, pedagogical talk about how they have learned to grow epitaxially nice structures between van der Waals magnets (like Fe3GeTe2) and topological insulators (Bi2Te3).   This was followed by a tag-team talk by Vishakha Gupta and Thow Min Cham from Cornell, presenting some great results about spin orbit torque measurements coupling topological insulators and van der Waals magnets, where a gate can be used to dial around the chemical potential in the TI, leading to changes in the anomalous Hall effect.
• I did check out the history of science session, featuring a very nice talk about the 75th anniversary of the foundations of quantum electrodynamics by Chad Orzel, including a book recommendation that I need to follow up on.
Overall, it was a good meeting, certainly the closest thing to a "normal" March Meeting since 2019.  I'm not a fan of Las Vegas as a venue, though.  The conference center was a bit too small (leading to a genuinely concerning jamming transition in the hallways at one point), the food was generally criminally expensive, and too many places indoors smelled like a combination of ancient cigarette smoke and ineffective carpet cleaner.   It will be interesting to see what the stats are like for things like the downloads of recorded talks and viewing of the virtual component of the meeting that happens in ten days.

## Thursday, March 09, 2023

### APS March Meeting 2023, Day 3

There is vigorous discussion taking place on the Day 2 link regarding the highly controversial claim of room temperature superconductivity.

Highlights from Wednesday are a hodgepodge because of my meanderings:

• The session about quantum computing hardware was well attended, though I couldn't stay for the whole thing.  The talk by Christopher Eichler about the status of superconducting qubit capabilities was interesting, arguing the case that SC devices can credibly get to the thresholds needed for error correction, though that will require improvements in just about every facet to get there with manageable overhead.  The presentation by Anausa Chatterjee about the status of silicon spin qubits was similarly broad.  The silicon implementation faces major challenges of layout, exacerbated (ironically) by the small size of the physical dots.  There have been some recent advances in fab that are quite impressive, like this 4 by 4 crossbar.
• Speaking of impressive capabilities, there were two talks (1, 2) by members of the Yacoby group at Harvard about using a scanning NV center to image the formation and positions of vortices in planar Josephson junctions.  They can toggle between 0 and 1 vortices in the junction and can see some screening effects that you can't just get from the transport data.  Pretty images.
• Switching gears, I heard a couple of talks in an invited session about emergent phenomena in strongly correlated materials.  From Paul Goddard at Warwick I learned about charge transport in some pyrochlore iridates that I didn't realize had so much residual conduction at low temperatures.  See here.  Likewise, James Analytis gave a characteristically clear talk about interesting superconductivity in Ni(x)Ta4Se8 (arxiv version here), an intercalated dichalcogenide that has magnetism as well as re-entrant superconductivity up at the magnetic field that kills the magnetically ordered state.
• Later in the day, there was a really interesting session about measuring entropy, which is notoriously difficult to do.  As I've told students for years, you can't go to Keysight and buy an entropy-meter.  There was some extremely pretty data presented by Shahal Ilani using a variant of their new scanning probe technique.
Morning of Day 4 is being taken up by a bunch of other tasks, so the next writeup may be sparse.

## Tuesday, March 07, 2023

### APS March Meeting 2023, Day 2

I ended up spending more time catching up with people this afternoon than going to talks after my session ended, but here are a couple of highlights:

• There was an invited session about the metal halide perovskites, and there were some interesting talks.  My faculty colleague Aditya Mohite gave a nice presentation about the really surprising effects that light exposure has on the lattice structure of these materials.  One specific example:  under illumination, some of the 2D perovskite materials contract considerably, as has been seen by doing in situ x-ray diffraction on these structures.   This contraction leads to a readily measured increase in electron mobility and solar cell performance.  Moreover, the diffraction patterns show that some diffraction spots actually grow and get sharper under illumination.  This kind of improved ordering shows that this is not just some sort of weird heating effect.
• In a session about imaging, I caught an excellent talk by Masaru Kuno, who described his spectroscopic infrared photothermal heterodyne imaging.  The idea is elegant, if you have access to the right light source.  Use a tunable mid-IR laser that can go across the "fingerprint region" of photon energies to illuminate the sample in a time-modulated way.  If there is an absorptive mode (vibrational in a molecule, or plasmonic in a metal) there, the heating will cause a time-modulated change in the local index of refraction, which is then detected using a visible probe beam and a lock-in amplifier.  It was an extremely clear, pedagogical talk.
• I spent much of my time in the strange metal session where I spoke.  There were some very good (though rather technical) theory talks, trying to understand the origins of strange metallicity and key issues like the role of disorder.
I had wanted to attend the session about superconductivity measurements in materials at high pressures, because of the recent and ongoing controversies.  However, the room was small and so packed that the fire marshal was turning people away all afternoon.  I gather that it was quite an eventful session.  If one of my readers was there and would like to summarize in the comments, I'd be grateful.

(BTW, it seems like this year there have been two real steps backwards in the meeting.  The official app, I am told, is painful, and for the first time in several years, the aps wifi in the meeting venue is unreliable to the point of being unusable.  Not great.)

### APS March Meeting 2023, Day 1

Ahh, Las Vegas.  I will say, I think every APS March Meeting from now on should have a giant Ferris wheel right by the registration lobby.

Here are a few highlights from what I saw after I arrived around lunchtime today:

• Given some of my current research, I spent a fair bit of time at the invited session about strange metals today.   All of the talks that I saw were very strong.  Andrew MacKenzie spoke about recent measurements of the Lorenz number in such materials (particularly Sr3Ru2O7) and made a persuasive case that strange metals do look different in their temperature-dependent thermal conductivity, because of very strong electron-electron scattering.  This is discussed in this recent review article.
• In the same session, Brad Ramshaw showed very pretty angle-dependent magnetoresistance data on Nd-LSCO, an archetypal cuprate, arguing that the whole data set can be modeled very well assuming conventional quasiparticles and Boltzmann equation analysis (albeit with a funky combination of temperature-independent anisotropic scattering and strongly temperature dependent isotropic scattering).  His postdoc Gaël Grissonnanche expanded on this and looked at how such a model can also reproduce the linear-in-B magnetoresistance in this system.
• At the McGroddy Prize session, James Hone gave a very nice overview of the impressive body of work from Columbia over the years on all of the stackable van der Waals materials.  Some particular recent highlights included: (1) using deliberately oxidized WSe2 (into WOx) as a low-disorder, very high workfunction material that modulation dopes holes when stacked on a target layer of interest; (2) Using vdW material ferroelectricity to modulate superconductivity in MoTe2; in-progress work using an AFM + an hBN "handle" to bend a graphene "noodle" to get continuously tuned, clean moiré potentials; and electrostatically actuated sliding motion of monolayer vdW material.
Hopefully crowd control will be a bit better tomorrow.  The hallways seemed narrower than at past meetings, very crowded, and the site would benefit from more places to sit and have conversations.

## Sunday, March 05, 2023

### APS March Meeting 2023 - coming soon

I will be attending the 2023 APS March Meeting in Las Vegas this week.  I will do my best to try to report on some highlights daily, though that may be more challenging than usual for me this time around (looming proposal deadline that I suspect all of my condensed matter faculty readers know about, plus some teaching-related work).  This is the first APS meeting in Las Vegas since 1986, when (according to legend) the APS was invited not to come back.  (Sorry for the web archive link - it would appear that the old PhysicsCentral content from APS is not online anywhere easily searchable.)  I'll be giving an invited talk on Tuesday which should be fun.  If people have suggestions of particular exciting sessions, please add them in the comments.

## Monday, February 20, 2023

### Science and how it will be practiced in the future

I just registered for an event that celebrates the 35th anniversary of a particular science and engineering program, and one question they posed was, to paraphrase, "Science has changed a lot in the last 35 years.  Please make three predictions about science in the next 35 years."

I'd be curious for readers' views on this.  My quick take:

• There will be far more AI/machine learning/software agent-assisted activity.  That seems a certainty, and hopefully it may alleviate some repetitive drudgery in certain types of research.
• Hopefully I am wrong about this, but I have a feeling that we are still trending in the direction of a widening divide between "have" and "have not" research universities, in terms of having the financial resources to do leading science and engineering research.
• Foundation investments may be a growing portion of basic research support, for good or ill.  Governmental agencies will face increasing constraints on finances and pressure to concentrate more on short-term and applied work with some claimed quick benefit to economic competitiveness or national security.
Thoughts?

## Thursday, February 09, 2023

### Tour de force work: Bragg, diffraction, and diamond

There are some examples of scientific progress that just seem so far above and beyond the norm, it's almost jaw dropping in terms of the mental leap needed for the insight.  One example that I always liked to point out to first-year undergrads learning about gravity is Johannes Kepler in 1601-1609 analyzing Tycho Brahe's data by hand (obviously) and deducing that planets move in elliptical orbits and the associated laws of planetary motion.  Imagine staring at page after page of hand-written numerical tables and somehow seeing that.

 Left: X-ray diffraction from single-crystal diamond. Right: Bragg's calculation of wherethe spots would be if diamond had what we now know is the correct structure.
Another example from condensed matter physics is the 1912 discovery by William Lawrence Bragg, then 25 years old, that he could deduce the crystal structure of solids from the positions of the spots revealed on photographic film as the solid diffracted a beam of x-rays.  The very fact of diffraction of x-rays by crystals had only been found earlier the same year by von Laue and collaborators.  Bragg had the insight that interference effects due to the x-rays bouncing off different planes of atoms would determine the pattern of spots, as constructive interference only takes place for certain combinations of directions for a given wavelength of x-rays.  The image here is based on Figs. 11 and 12 from this paper, "The Structure of Diamond", by Bragg and his father (who built the diffractometer!).  That was published back-to-back with the more general (and single-author!) paper, "The Structure of some Crystals as Indicated by Their Diffraction of X-rays", where Bragg wrote what is now known as Bragg's Law and the prescription for finding the distance between adjacent planes of atoms.  Imagine looking at the smudgy spots on the photographic plates, having the "aha!" insight about the origin of the pattern, and having the raw computational prowess to just go ahead and calculate it.  Unreal.

## Sunday, February 05, 2023

### Some interesting links - useful lecture notes, videos

Proposal writing, paper writing, and course prep are eating a lot of my bandwidth right now, but I wanted to share a few things:

• David Tong at Cambridge is a gifted educator and communicator who has written lecture notes that span a wide swath of the physics curriculum, from introductory material on mechanics through advanced graduate-level treatments of quantum field theory.  Truly, these are a fantastic resource, made freely available.  The link above goes to a page with links to all of these.
• In a similar vein, Daniel Arovas at UC San Diego has also written up lecture notes on multiple components of physics, though usually aimed at the graduate level and not all linked in one place.  These include (links to pdf files) mechanics, thermodynamics and statistical mechanics, condensed matter physics, nonlinear dynamics, the quantum Hall effect, and group theory (unfinished).
• I long ago should have mentioned this youtube channel (Kathy Loves Physics and History), by Kathy Joseph.  Her videos are a great blend of (like it says on the label) physics and history of science.  As a great example, check out the story of Ohm's Law.  I had never heard about the dispute between Ohm and Ampère (who didn't know about the internal resistance of batteries, and thus thought his experiments disproved Ohm's law).
• This twitter thread pointing out that current in quantum Hall and related systems is not, in fact, purely carried by states at the sample edges, is thought-provoking.

## Friday, January 27, 2023

### Cavities and tuning physics

I've written before about cavity quantum electrodynamics.  An electromagnetic cavity - a resonator of some kind, like your microwave oven chamber is for microwaves, or like an optical cavity made using nearly perfect mirrors - picks out what electromagnetic modes are allowed inside it.  In the language of photons, the "density of states" for photons in the cavity is modified from what it would be in free space.  Matter placed in the cavity, e.g. an atom, then interacts with that modified environment, even if the cavity is not being excited.  Instead of thinking about just the matter, or just the radiation by itself, in the cavity you need to include the light-matter interaction, and you can end up with states called polaritons that are combinations of matter + radiation excitations.  There are various flavors of polaritons, as there are different kinds of cavities as well as different kinds of matter (atoms vs. excitons, for example).

I just heard a nice talk by Angel Rubio about recent advances in applying cavity effects to both chemistry and materials properties.  For a recent discussion of the former, you can try here (pdf file).  Similar in spirit, there is a great deal of interest in using cavity interactions to modify the ground states (or excited states) of solid materials.  Resonantly altering phonons might allow tuning of superconductivity, for example.  Or, you could take a material like SrTiO3, which is almost a ferroelectric, and try to stabilize ferroelectricity.  Or, you could to take something that is almost a spin liquid and try to get it there by putting it in a cavity and pumping a little.

It's certainly interesting to ponder.  Achieving this in practice is very challenging, because getting matter-cavity couplings to be sufficiently large is not easy.  Never the less, the idea that you can take a material and potentially change something fundamental about its properties just by placing it in the right surroundings sounds almost magical.  Very cool to consider.

## Sunday, January 15, 2023

### Condensed matter’s rough start

I’m teaching undergrad solid-state for the first time, and it has served as a reminder of how condensed matter physics got off the ground.  I suspect that one reason CM historically had not received a lot of respect in the early years (e.g. Pauli declaring that solid-state physics is the physics of dirt) is that it began very much as a grab bag of empirical observations, with the knowledge that the true underpinnings were well out of reach at the time.  Remember the order of a few key discoveries:

A whole host of materials physics observations predate the discovery of the electron, let alone modern statistical physics and quantum mechanics.  The early days of condensed matter had a lot of handwaving.  The derivation of the Hall effect in the classical Drude picture (modeling electrons in a metal based on the kinetic theory of gases) was viewed as a triumph, even though it clearly was incomplete and got the sign wrong (!) for a bunch of materials.  (Can you imagine trying to publish a result today and saying, ‘sure, it’s the wrong sign half the time, but it has to be sort of correct’?)

That we now actually understand so much about the physics of materials is one of the great intellectual accomplishments of the species, and the fact that so much of the explanation has real elegance is worth appreciating.

## Saturday, January 07, 2023

### News items for the new year

After I was not chosen to be Speaker of the US House of Representatives, I think it’s time to highlight some brief items:

• Here is a great blog post by a Rice grad alum, Daniel Gonzales, about flow to approach faculty searches.  I had written a fair bit on this a number of years ago, but his take is much fresher and up to date.
• My colleagues in Rice’s chem department have written a very nice obituary in PNAS for Bob Curl.
• It’s taken nearly 2000 years, but people seem to have finally figured out the reason why Roman concrete lasts hundreds to thousands of years, while modern concrete often starts crumbling after 30 years or so.
• Capabilities for quantum optomechanical widgets are improving all the time.  Now it’s possible to implement a model for graphene, following some exquisite fabrication and impressive measurement techniques.
• From the math perspective, this is just f-ing weird.  For more info, see here.