Twisted graphene has become the big thing in physics | Hacker News Reader

Twisted graphene has become the big thing in physics

quantamagazine.org

261 pointsfurcyd102 comments

Fairly shocking to me that Yuan Cao received literally a single glancing mention here, but he was clearly the one who actually made the pivotal discovery, and is the first author on the Nature paper (https://www.nature.com/articles/nature26154), and was the one named to the Nature 10 in 2018 for his discovery.

Really mind boggling that this entire piece focuses all the attention on his supervisor and almost neglects to mention him at all.

Usually the grad student does most of the work, but the ideas and direction comes from the supervisor. It's normal that the supervisor funds, directs and communicates the work that's being done. More often than not, the supervisor has a better idea of the big picture and the implications of the work than the grad student, so it's natural that the supervisor talks to the press.

For example, I'm a grad student, in a department where my supervisor would talk to the press on work that I would have done.

In CS related fields, in particular ML and CV, this is absolutely not the usual situation except perhaps in the beginning of the PhD. Perhaps it's more common in fields where the research is done on top of a heavy investment in infrastructure/equipment that is lead by the professor, e.g. in physics and biology?

In my experience in biology new professors provide a lot of ideas, old professors just steal new ideas from their students and post docs.

> Yuan Cao ... was clearly the one who actually made the pivotal discovery

Are you saying that based on something external to the paper? In the author contribution section, Cao is not credited with having done anything on his own:

> Author Contributions

> Y.C., J.Y.L., J.D.S-Y fabricated the devices and performed transport measurements. Y.C., V.F. performed data analysis. P.J.H. supervised the project. S.F. and E.K. provided numerical calculations. S.L.T., A.D. and R.C.A. measured capacitance data. K.W. and T.T. provided h-BN devices. Y.C., V.F., and P.J.H. wrote the paper with input from all authors.

The first authorship is an important meaningful thing, but it definitely isn't a guarantee that they key, most noteworthy step was done by the first author, much less the first author alone.

Pretty typical of academia. Grad students also don't normally get Nobels

And for good reason. A responsible supervisor will typically give PhD students tasks that he has already "kind-of / sort-of" worked out as feasible. I once read the following recommendation for how to set dissertation subjects, I can't recall by whom.

- BSc thesis: what I can do over lunch

- Master thesis: what I could do in an afternoon

- PhD thesis: what I could do in a week

(Here the figures don't mean typing, programming etc, but the core intellectual work). After having supervised nearly 200 theses are BSc, Masters and PhD level, I must agree, this is a pretty great heuristic.

Note: there are exceptions. Some PhD theses go way beyond this, but those are rare. I have no idea about Yuan Cao's work, discussed here.

Where are you in the world that the level of sophistication of the work being set is such that this heuristic holds true?

I suppose a BSc thesis or design report etc. is supposed to be more of an exercise in demonstrating some understanding and creating something, but beyond that I would expect some fairly novel impact from an MSc and definitely from a PhD.

I'm very surprised by this as the quality of MSc theses and PhD theses at the universities I attended were all fairly novel, and even if the supervisor had suspected the same conclusion, the amount of work to arrive at that conclusion is non-trivial when doing research.

I fear this devalues the contribution of what these young researchers are doing. I know many people who went on to very good research positions and even founded companies based on their Masters or PhD work.

None of this applicable for hard experimental sciences like physics and chemistry. You can't shortcut bench time, especially since it involves a lot of trial and error. And sometimes it doesn't work out, at all.

What field are you in? This applicability of this strikes me as wildly different depending on the field and the standards of the university.

Cynical me asks isn't that how it works for PhD students?

Yes, probably.

>Even without superconductivity, ordinary computers and other electronics could get a huge boost in performance versus cost from twistronics, due to the fact that entire complex electronic circuits could in theory be built into a few sheets of pure carbon, without needing a dozen or more complexly etched layers of challenging materials common to today’s chips.

Does anybody know if the environmental impact of graphene is supposed to be any better than that of plastic? Does it break down more easily as it is so thin? I’m worried we may outdo ourselves with the magic compound of the century...

Graphene nanoparticle toxicity is under active study. It seems to depend on the form and size of the graphene structure.

* Carbon nanotubes may be as dangerous as asbestos for similar reasons. They act like spikes that stick into cells.

* Graphene nanoplatelets are shown to trigger the inflammatory response (in vivo and in vitro) in lung cells. Something that normal carbon black don't do.

Another major 'environmental' impact that may be very nefarious is the health effect of such nano-materials.

We don't want to re-create all the mess that we have today form asbestos -- which was also a wonder-material at the time.

The problem with asbestos wasn’t really the toxicity per se, it’s that the companies using it hid the toxicity to avoid having to do all the expensive safety steps that would let them use asbestos without killing people. We can avoid this with carbon nanotubes and similar if we’re honest about the risks and careful with how we handle them.

This will probably happen again given all the money that's on the line.

The fact that we’re talking about it here implies that we’re in a better place than we were a century ago.

A century ago yes, fifty years ago I'm not so sure, thirty years ago almost certainly not.

There's at least a little bit of study regarding graphene toxicity. Hopefully nothing as massive as asbestos will ensue.

Yes. There’s not applicable commercially viable things based on graphene yet. But superconductivity will be a revolution in many ways and especially in computing.

I don’t think there’s any indication that this will work at temperatures far from absolute zero, though.

Superconductivity would revolutionize transportation, low cost medical imaging with MRIs, and weapons. Lots of weapons.

You're forgetting the two most important; energy storage and transport.

Yeah, imagine if we could more or less losslessly transfer electricity over vast distances. Massive renewable energy farms could be built wherever there was sun/wind/rivers whether the energy consumers are close or not. Energy could be sent to pump water into reservoirs as huge centralized batteries. The problem with 'what happens when the sun isn't shining/the wind isn't blowing' could be sidestepped because it's always sunny/windy somewhere, so we just get the power from as far away as needed.

People seem to underestimate how efficient regular power lines are. The continent-spanning european power grid has a total transmission loss of about 6% using 19th century technology (transformers and copper wires). Modern high voltage DC lines can perform even better. The main limitation seems to be that people don't want to have power lines in their back yard. Not something that superconductors are going to sove.

Also the cost of a equivalent superconductor network would be an order of magnitude more expensive that what is essentially room temperature metal cables with very basic technology - transformers, insulation, and switchgear.

A superconducting power network could be built today - it would consist of a pair of ceramic superconductors suspended in a liquid helium pipe, wrapped with 3 feet of insulation.

Every few kilometers, one would need liquid helium pumping and chilling plants.

Total helium losses to leakage wouldn't be too big. Electricity transmission efficiency would be reduced by all the chilling gear running, but still better than regular conductors.

The only real barrier is cost. Not even the cost of the superconducting material. You can't hang a 6 feet diameter pipe on pylons across the nation - you're going to have to bury it, and that's going to get exxxxxpensive fast!

> The only real barrier is cost.

I feel like this could almost be a slogan for the human race at this point. Our grasp of science and engineering has reached a level where's there's very few things we might want to build where we couldn't conceivably do it. We could build the most outlandish megastructures, infrastructure and space bases if we really had to, but it all just costs too much.

"It's expensive and we couldn't find investors" really means "It's a lot of work, and nobody thinks it'll be worth it".

We might be able to anything, but the capitalist system stops us doing things that don't look profitable.

Profitability at time X is a pretty decent heuristic for whether something is worth doing at time X.

How do you know that? Unknown unknowns.

Unknown unknowns are more likely to cause problems and delay completion, not accelerate development.

> ...suspended in a liquid helium pipe...

Where would we get enough helium to cover more than a small city's worth of power transmission lines?

Is the amount of energy you spend building and maintaining that network more than what you're already losing to inefficiency?

Interesting video on Chinese 'supergrid' from coal plants in the west, to the population centers in the east, a total length of 3,324 km (2,065 miles):

https://www.youtube.com/watch?v=wfG0USvDTew&t=686s

To increase efficiency, they are increasing the voltage to 1.1 MV:

https://www.youtube.com/watch?v=wfG0USvDTew&t=780s

Since the population and the generation is intermingled, the average joule of energy actually doesn't travel far. Perhaps only a few hundred km.

Increasing power transfer effectiveness by even 1% seems like it would be a huge improvement when you consider the energy demands of a continent. That's potentially a lot of CO2 saved.

I find it hard to tell if you're serious or not. To a rough approximation this is exactly how it works today.

Reminds me that I need to check performances of graphene supercaps featured electric engines.

I understand what superconductivity is and how it can revolutionize things in general. But why those things in particular? So transport for example - better maglev trains?

MRI’s use helium cooled magnets to create extreme magnetic fields. That cooling costs a lot...

A huge amount of energy is wasted distributing electricity for 10s of thousands km. I am not sure how it can help storage though, even if you theoretically can let the electricity spin in a closed loop forever the energy density seems way too low to me.

Graphene based supercapacitors have huge capacitance because graphene is single atom thick, so you can put a lot of layer of this material increasing total surface area hence capacitance for same volume of capacitor space used.

Here's to hoping my phone has enough milliamps to stay alive for more than 8 hours and that this happens in my lifetime. #firstworldproblems for sure but come on it would be really cool.

I've same problem, it's now less bad with Quick Charge and Powerbank combo but still bad.

A standard 380 kV power line has a loss on the order of 1% per 100 km. Unless you want to span large continents, this doesn't seem like a big limitation at all.

Power Lines are several hundreds of km and even only 1% of the global electric production seems a huge amount to me... But in reality it is much more, in US is 5%: https://www.eia.gov/tools/faqs/faq.php?id=105&t=3

These numbers show that the grid is already 95% efficient! It makes much more sense to improve the really inefficient parts, such as power plants and electricity consumers.

So how is that coming along. It seems like I've been hearing about graphene for ages now.

Mass scale applications are just around the corner -just like batteries that have 600% more capacity than current batteries.

Define 'ages'

For me, a decade since I last touch the stuff for my PhD thesis.

Ever since the physicist got a Nobel prize for it. I don't remember who it was and when it happened (I'm too lazy to Google it right now).

Holy guac, room temperature superconductivity seems almost science fiction-y but just imagine the disruption it would make. I would be particularly excited to experience how much electric motors and energy transfer/storage and conversion would improve.

Apparently they reached superconductivity at 3K. Hardly room temperature.

The thing is they can use it to understand superconductivity because there are vastly fewer variables involved. It could lead to room-temperature superconductivity, assuming it even exists.

However this method is completely different and thus might open more options

Vs. cryogenic superconductors is a radically different phenomenon.

And death rays. Don't forget about the death rays!

Pardon my interruption but I searched for 'use' or 'usage' and came up empty. Anyone can tell a regular guy why it's a big deal and what are the applications? ta

Research. It's a relatively simple setup with relatively easy to control properties, that does something really fucking weird. It offers a window into the behavior of other poorly understood superconductors, and that offers the eventual chance of higher temperature or higher magnetic flux superconductors. Either would be revolutionary - room temperature superconductors have obvious applications, but higher flux superconductors would allow better, smaller, cheaper stellarators and tokamaks - opening the door for fusion power.

It seems to have a very real potential to help us learn a great deal about superconductivity.

>>> The stakes in the race to come up with easier to make, better performing, higher-temperature superconductors are huge. Aside from the oft-evoked vision of levitating trains, reducing the energy loss in electric power transmission would boost economies and sharply cut harmful emissions around the world. Qubit fabrication could suddenly become practical, perhaps ushering in the rise of quantum computers. Even without superconductivity, ordinary computers and other electronics could get a huge boost in performance versus cost from twistronics, due to the fact that entire complex electronic circuits could in theory be built into a few sheets of pure carbon, without needing a dozen or more complexly etched layers of challenging materials common to today’s chips. “You could integrate wildly different properties of matter into these circuits right next to one another, and vary them with local electric fields,” said Dean. “I can’t find words to describe how profound that is. I’d have to make something up. Maybe dynamic material engineering?” >>>

Buckyballs have mass, yet exhibit wave interference. We can make them bigger and bigger, and focus them as if they classically popped into existence.

I wonder if it holds up on very large scales, like if we can cover an atmosphere, or a star in one. What would that mean? Elements now are just variations of carbon structures?

And could we at that level build a virtual one? Develop some exotic particle in the atmosphere, get really precise at moving it around, and model the entire Earth, Solar System or Galaxy as interactions as fullerenes?

Just thinking.

Superconductors = flying cars. Finally they are working on something useful!

Better make watertight social control devices if you want to hand everyone alien nose hair trimmers that can level city's. Same for the flying cruise.. Cars.

Some exponential tech, always seems to be 30 years away from legacy humanity. Thank you moderators.

> Pablo Jarillo-Herrero is channeling some of his copious energy into a morning run, dodging startled pedestrians as he zips along, gradually disappearing into the distance.

Can someone please write up TL;DR about the actual science without the details on what kind of coffee did the author sip while taking the interview?

When two sheets of graphene are stacked, and twisted with respect to one another, they form a metameterial, with properties partially dependent on the twist angle.

At a twist angle of 1.1 degrees, the energy required for an electron in one sheet to tunnel to the other sheet drops to zero.

The problem is that certain angles represent a lower-energy state than others, so twisting to a magic angle also requires overcoming some buckling and creasing in the individual sheets, that allow regions to locally align to a non-magic angle (like zero degrees). This confounds measurements of the properties of the metamaterial.

Certain angles have been shown to exhibit superconductivity. While less useful than previously discovered superconductors for the purpose of moving electrons, these are more useful for studying superconductivity itself, because the superconductor is 2.5d, composed of a single type of atom, each with identical bond configurations. A lot of the variables that appear in other superconductors drop out.

You're a much better popular science writer than the author of the original article. Thank you.

No mention of ballistic conductivity in CNTs which is well known, this is obviously very different?

Where'd all the intelligent comments go? Hackernews used to be a cut above when it came to an intelligent comments section. Where'd all those people go, is there a new place to hang out?

If you know th new place, you know the first rule of the new place...

A nice intro to superconductors http://www.superconductors.org/uses.htm

the history of graphene, the "next best thing" since forever: https://graphene-flagship.eu/material/Pages/The-history-of-g... (previous HN discussion - https://news.ycombinator.com/item?id=8751946 )

Careful, we shoot the messenger these days.

Is this a bigger thing than borophene which was a big thing a few weeks ago?

I'm gonna say "no". This is only relevant in that it might lead to better understanding of superconductivity. When the models can predict this, they will have made progress.

So... I’m an idiot but I have a question: could this theoretically allow for a battery that never loses a charge and/or charges instantly?

FWIW— I literally know almost nothing about superconductors...

No, because that would violate the Law of Conservation of Energy, which according to our current understanding would imply that this form of "perpetual motion" is impossible as long as the system experiences some sort of load. [0]

[0] https://en.wikipedia.org/wiki/Conservation_of_energy

I don’t think I’m talking about perpetual motion at all...

When I say never loses a charge I don’t mean it’s limitless capacity. I mean it could be charged 1,000,000 times without any affect on the capacity of the system? Maybe a better way to say it, a battery that does not degrade with each use.

Superconductors allow for the perfect transfer of electrons without any loss? So like if I had a giant earth sized graphene wire superconductor for this example: could I have the energy travel around the ring indefinitely so long as it’s closed?

Ok I see, by "not losing its charge" you meant not wearing down from repeated use. Technically speaking the charge would be the amount of electrical potential energy stored in the device.

This system is still subject to the laws of thermodynamics, however.

AFAIK ideal superconductivity does not exist outside of theoretical physics, just as ideal platonic solids do not exist in the real world. Things get bumpy close up, and then they get fuzzy.

Even if you could maintain a "perfect loop" of electrons along a wire, perfectly insulated from outside forces including EMI and gravity, any observation of the system would still introduce entropy from the outside world and eventually degrade the system unless it is self-correcting.

An ambient self-correcting conductor would be a massive breakthrough.

Charge is not amount of electric potential.

Charge is a property of matter which causes experiencing a force when placed in an electric field.

Strength of the electric field is electric potential.

And charges arrange in some form under this field which wouldn't be so in absense of this field and how tight is that form depends on the strength of electric field. And this can be used to perform some work but this is not storing charge as the total charge before arrangement is same as total charge after arrangement there is no new charge added. We are storing electric field here.

In all such storage devices, strength of the field goes down after sometimes.

No I don't know how it can help in case of batteries but assuming you use capacitor to store electric field the leakage can be decreased by using better insulation which in many cases is thicker and the capacitor is limited to some specific size, if you can decrease the surface area of the conductive plates, you are able to use thicker insulation which results in lower leakage so graphene can help here as it's just one atom thick.

> Charge is a property of matter which causes experiencing a force when placed in an electric field.

From Wikipedia [0]:

"A battery's capacity is the amount of electric charge it can deliver at the rated voltage."

Another way of saying this is that a battery can store potential electric charge which is discharged from the battery during use. The maximum potential electric charge a battery can store is its capacity.

Similarly, a rock raised above your head is not "storing gravity", but it still contains gravitational potential energy.

When we talk about batteries however, we tend to colloquially refer to this electrical potential as "charge" due to the way words like "charger" and "discharge" have entered the vernacular. Phrases like, "How much charge does your phone have left?" has become increasingly common.

This is distinct from the definition of electric charge that you lifted from Wikipedia's page on "electrical charge". It's just the way language has evolved.

> And charges arrange in some form under this field which wouldn't be so in absense of this field and how tight is that form depends on the strength of electric field. And this can be used to perform some work but this is not storing charge as the total charge before arrangement is same as total charge after arrangement there is no new charge added.

We are not measuring the total charge. We are measuring the electrical potential across a circuit. The total "charge" remains the same, but the electrical potential decreases when the battery discharges.

[0] https://en.wikipedia.org/wiki/Electric_battery#Capacity_and_...

The second law of thermodynamics basically stipulates this is impossible. All materials wear out no matter what, even black holes eventually turn to entropy. You could create one with much better resistance to wear, but never completely resistant. Also I doubt true superconductors exist, it may be their losses exist below measurement error, but the fact that electrons are in relative motion, and are subject to the effects of the world around it, they must lose energy at some point.

Edit 1: Second, not first law Edit 2: In your second paragraph, you literally described a perpetual motion machine, electrons going around a circuit is still 'motion'

Um, no there are such things as frictionless machines which without interruption can run forever. That’s actually what superconductivity is—moving electrons without resistance (friction).

That is what superconductivity is defined as, perhaps, but I'm saying, no such material is, nor can any construct be built to insulate a subset of the universe from the rest of the universe. So even if you magically made a material that in itself causes no friction, the electrons still have the rest of the universe to deal with. For example, how would electrons go around corners without having a force applied on it? How do you prevent magnetic interactions of electron in motion with things beyond the material from causing friction?

I'm definitely not an expert, but just because you need force to go around corners doesn't mean you need work. An unchanging magnetic field in fact exactly accomplishes this, as it always accelerates an electron perpendicular to its motion, thereby leaving the energy of the electron unchanged.

That sounds a lot like a slingshot maneuver around a planet to get more momentum. Strictly speaking you're taking energy from the planet/sun to do so. An unchanging magnetic field still exists in the real universe, and I find it difficult to believe that it would be completely unaffected by the interaction. fwiw I'm also no expert

edit: I'm taking unchanging to be a practical implementation of say a permanent magnet here, rather than a theoretical construct.

It is clearly possible to change the direction of an objects movement without doing work on it, if you consider forces perpendicular to the direction of movement.

In other words, you can change the direction of the velocity vector without doing work, as long as the magnitude stays the same (ignoring potential energy here).

In fact, a magnetic field is unable to do work, since it always acts perpendicular to the direction of movement of the charge that it acts upon.

no, what I'm talking about is more like a perfectly circular orbit around the sun, where the direction of the acceleration is always exactly perpendicular to the motion.

But there is no perfectly circular orbit around the sun. The mass of the two bodies causes the center of mass to be slightly off center from the sun, and both the sun and earth orbit around this center of mass in a fashion that AFAIK loses energy.

If the two objects were either perfect spheres or tidally locked, then a circular orbit would continue forever. There are no losses due to pure motion in a vacuum.

I thought the theme of my reply is that we're not talking about theoretical constructs, but instead reality... Space is not a vacuum, just much lower pressure than on earth.

It is a really cool discovery, but it is still not room temperature superconductivity...

It's great that now that regular graphene has become ubiquitous and has delivered on all of its promises to revolutionize tech we have something new to look forward to.

It's the future, and always will be :)

Is there a list of devices regular graphene has made possible?

I believe he is being sarcastic

Rats. I got excited for a second.

Its quite shocking to see that the hard bonded carbon sheets can also move in spite of their large forces of attraction betweeb them . Well its other effects would be overwhelming ..

YAAWWWWN.

Graphene was going to transform everything. Years ago.

Vittoria, a tire company have used Graphene tech of sorts in their bicycle tires: https://www.vittoria.com/us/graphene-technology

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