spxtr

I thought this was a hilarious comment, for what it's worth.

Pretty funny.

Having taught low-temperature condensed matter labs, a big part of the grade is figuring out what went wrong, and either correcting for it, or at least acknowledging that it went wrong. The student needed to give more information about the experimental setup (what instruments did they use? four point or two point resistance? resistivity vs resistance? what is R_0?) and why they think the experiment didn't work. It looks to me like they had something miswired, so they only measured noise.

ET Jaynes has a book "Probability Theory: The Logic of Science". It's a nice book, and I was wondering if you had any thoughts on it.

Do you disagree with ET Jaynes then?

They won't, but MoS_2 very well could be.

Superconductivity in TBG was originally sold as "unconventional". This article reaffirms that claim by showing how it cannot be a BCS superconductor, and more. Very interesting.

It's worth reiterating that while graphene can have some niche uses in "the real world", the main reason that it is so highly prized within academia is that it is a superb platform for studying fundamental physics, as in this work. Maybe in the future this will lead to room-temperature superconductors or something along those lines. Maybe not. Nobody jokes about how the Higgs boson has failed to leave the lab.

The other problem with this approach is that it is limited to 50% efficiency long-term. They claim "up to 90%", but it is only 90% efficient immediately after switching directions. The efficiency then drops to 0% before switching modes again.

Matt Yankowitz' "Tuning superconductivity in magic-angle graphene" shows how hydrostatic pressure affects TBG magic.

I was measuring a delicate electronic device at MagLab in Tallahassee. They warned me that the best data would be had at night, because of reduced noise from a nearby radio station. Precisely at 8 PM every night my data became noticably sharper.

Particle physics does not include that. There is no evidence that superconductivity requires any physics outside of the standard model.

You can probe different areas of the same device by adding many electrical probes, usually in a geometry called a Hall bar. In the old days of TBG, the different regions of the same device would do wildly different things. These days we are much better at stacking, and the different regions of the same device will be mostly the same.

The mechanical tearing imparts the strain. Probably. Nobody really knows that for sure.

These days, common practice is to cut the graphene with an AFM or laser prior to stacking.

https://www.nature.com/articles/s41586-019-1431-9 https://arxiv.org/abs/1812.08776

Lovely article.

> Creating a working device typically takes them dozens of tries. And even then, each device behaves differently, so specific experiments are almost impossible to repeat.

This is frustrating. You can make two twisted bilayer graphene samples at 1.10 degrees precisely (to within 0.01 degrees), and they will show completely different phase diagrams. One will superconduct, but the other will not. Things like that.

What I learned recently is that every transport paper's twist angle report is wrong. The two hypothetical samples are actually probably not both 1.10 degrees. The uncertainty in twist angle should be of order 10-20%, rather than <1%. I even made this same mistake in my own paper last year!

When creating these TBG samples, we used to literally tear the graphene in half, to get accurate relative alignment of the two halves. It was very clever, but it imparts a huge amount of strain to the two layers, generally of order 0.1-0.3%. This seems like a small amount, but moire patterns are extremely sensitive to this (roughly strain amount divided by twist angle, but the twist angle is very small), so the unit cell area gets modified by anywhere from 5-30%. In transport measurements, we can only measure moire unit cell area, but not twist angle. The number 1.10 +\- 0.01 deg is calculated assuming no strain, and this is an incorrect assumption. An STM paper from 2019 first pointed this out, but it was just a couple sentences buried in the supplemental material, and I (and most others) completely missed it.

Even four years after moire materials took over the condensed matter world, we still don't understand the basics of how the materials work. It's very exciting, hot stuff.

The article is from 2016, before she started her YouTube channel.

I'm probably misreading this, but I see "In this study, age ≥65 years, immunosuppression, diabetes, and chronic kidney, cardiac, pulmonary, neurologic, and liver disease were associated with higher odds for severe COVID-19 outcomes;" listed as the eight risk factors. Where are you seeing the ones you listed?

I have comcast internet with my own modem/router. Comcast will not give me a static IP unless I use their rental modem/router, which costs quite a bit monthly. I use ddns to work around this issue, and it mostly works fine.

It's sad that a great scientist got caught up in politics here. I suspect that if he had received money from any other country then he would have received a mere slap on the wrist.

Of course what he did was mega illegal and he knew it, but it's still sad.

I felt like this book was incredibly clever, but at times it felt like the pacing was infuriatingly slow. Especially near the start, it feels like there are too many chapters of world building per chapter of story.

Still, thoroughly enjoyed it.

> The new particle contains two charm quarks and an up and a down antiquark. Several tetraquarks have been discovered in recent years (including one with two charm quarks and two charm antiquarks), but this is the first one that contains two charm quarks, without charm antiquarks to balance them.

This is not the first time a tetraquark has been measured, but instead it's the first time a tetraquark with two charm quarks and no charm antiquarks. That's still nice work, but I was initially confused by the headline ("didn't they discover those already?").

I used to play a real-time version of this called Kung-Fu Chess. Each piece takes time to move to its destination, and when it arrives, a timer ticks down before that specific piece can be moved again. Very fun game.

https://en.wikipedia.org/wiki/Kung-Fu_Chess https://www.youtube.com/watch?v=fVob7meb83w

I don't understand what you are saying. The parent comment said that quantum allows a few types of operations to get faster, and your response was "No," followed by a specific algorithm that is faster. Where do you disagree?

Nice article!

Many of the cool excitonic properties that he describes were recently (last 10 years ish) seen in a class of materials known as TMDCs: https://en.wikipedia.org/wiki/Transition_metal_dichalcogenid...

Condensed matter physics is the largest field of physics by number of PhDs granted, but I feel like it gets a disproportionately low amount of pop sci coverage.

I personally think that the Hofstadter butterfly stuff is absolutely gorgeous, and it was a large part of why I started working on 2D materials in the first place.

https://en.wikipedia.org/wiki/Hofstadter%27s_butterfly

In the '70s, Hofstadter wrote about this neat fractal pattern that would show up in the band structure of a material in a sufficiently large magnetic field. Specifically, the magnetic field strength times the crystal unit cell area needed to be big. Magnetic field strength is limited by how much current you can put around a superconducting solenoid. Unit cell area is generally something that you can't change for ordinary crystals: it's just set by the chemistry of the material.

Back in 2012-ish, a few groups managed to artificially increase the area of the unit cell by multiple orders of magnitude by aligning the graphene with hexagonal boron nitride, which has the same crystal structure and a very similar size. When aligned, the moire pattern itself has a large size, and that was enough to see the butterfly.

I think CVD graphene (grown, production-scale stuff) has gotten to decent quality these days. There's much more to these devices than graphene, however.

You may have noticed that literally every experimental paper on this stuff has Kenji Watanabe and Takashi Taniguchi as authors. This is because they grow the best hBN crystals in the world and they give them for free to pretty much any researcher who asks nicely. This is amazing and without them the whole field would be way worse off. Their crystals are the bulk sort that needs scotch tape to use, much like graphite needs scotch tape to isolate graphene. I don't think CVD hBN is nearly as good as their stuff yet. The hBN provides an encapsulating dielectric for the graphene, and is critical to getting high-quality devices.

That's just one example of a problem with scaling this stuff, and there are others as well. The field is working to improve these things though, since right now it's super difficult to reproduce any given piece of physics. I think at this point there are exactly 3 ferromagnetic TBG devices in the world, for instance.

Graphene continues to impress condensed matter physics researchers. Just by taking this material made out of carbon atoms you can get superconducting states, correlated insulating states, ferromagnetism, and some others. By using field-effect-transistor-style device geometries, you can tune between these states by changing a voltage on a gate. This is a big deal, because it's much easier to change a gate voltage than it is to grow an entirely new material with a different doping level, which is usually what you need to do with other systems. The paper that this article is about is a nice measurement of the topological nature of the moire bands. It's cool stuff and could potentially be important for quantum computing, but don't forget that these devices are still extremely difficult to make.

Regardless of whether graphene has left the lab and made it into consumer electronics or not, it's still super interesting for academics.

Source: I work on this stuff.

Momentum is still conserved in quantum mechanics. This breaks the laws of physics regardless of whether or not it needs a constant energy source.

Does this name have any significance other than what you said here and what they say in this article?