[HN Gopher] The origin of the strong form of superconductivity
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The origin of the strong form of superconductivity
Author : nsoonhui
Score : 124 points
Date : 2022-09-22 12:18 UTC (10 hours ago)
(HTM) web link (www.quantamagazine.org)
(TXT) w3m dump (www.quantamagazine.org)
| mikewarot wrote:
| It's like ties in a railroad track, if you find a stride that
| matches an integer multiple of the tie distance you can run like
| it was normal ground.
|
| The natural "stride" of an electron might be more than 2.6
| nanometers. It could be they swing side to side a bit if the
| distance isn't quite right.
|
| Some experimentation is now in order.
|
| 2.6 Nanometers is about 5 atoms of silicon between peaks.
|
| I'm trying to find out the size of the cell created between
| sheets of graphene at the "magic angle" of 1.56 degrees.
|
| It may be that you simply need to _construct_ the right geometry
| between nodes to get superconductivity.
|
| Regardless of the underlying quantum mechanics, there's a large
| opening for experimental physics here. Are there edge effects,
| what about grain boundaries, etc.
| upsidesinclude wrote:
| Electrons don't have legs, but the concept might.
|
| How does the electron wavelength compare to the incidence of
| the geometry?
|
| Gamma = h bar/ momentum
|
| Where, m = m*v
|
| In a DC circuit the momentum can be held fairly stable once in
| a state of superconductance, but v is increasing up to the
| breakover point. Which in turn is decreasing wavelength. Bit of
| a trouble for a static 'circuit'.
|
| None of that is quantum anything, but it gets you thinking.
| mikewarot wrote:
| Electrons normally flow very slowly in a conductor, at about
| a snail's crawl. For a superconductor, I _suspect_ this is
| not the case... the quantity of electrons through a channel
| will go up, but the velocity is probably stable.
| tomxor wrote:
| That's an interesting idea, it sounds a lot like nanotechnology
| that exploits various quantum effects.
|
| My extremely layman understanding notices the currently known
| high temperature super conductors are crystalline, structure
| seems to matter, but whether a nanoscale structure above this
| could possibly have any significant effect? It would be nice to
| get the opinion of someone less vaguely educated on the subject
| :)
| durranh wrote:
| It's stories like these that keep me interested in physics
| sportstuff wrote:
| You may be interested in Physics of Pranayama(Breath). I hope
| someone would write up or research, Physics of Cancer. Physics
| is everywhere and all the time.
| RobertoG wrote:
| You can stop being interested in physics, but physics never
| stop being interested in you! ;-)
| whatshisface wrote:
| Or impartially disinterested in you, as the case may be.
| z2h-a6n wrote:
| As a physicist studying cuprates, I would caution that many of
| the strongest claims in the Quanta article are basically
| clickbait, especially the title of the article, and the notion
| that this experiment has solved the problem "to nearly everyone's
| satisfaction".
|
| The actual experiment and resulting paper [0] on the other hand
| are very good work, and may very well be right, but a substantial
| amount more work will be needed to determine how much of the
| rather unusual phenomenology of the cuprates is well-explained by
| superexchange interactions. I guess even more work will be needed
| to convince the majority of the field that this the right model
| for the cuprates, as opposed to any of the very many other models
| that have been proposed and studied in the past few decades. In
| particular:
|
| - High temperature superconductivity is not the only strange
| thing about the cuprates. The normal state (i.e. above the
| superconducting transition temperature) also has some rather
| unusual properties that are the subject of much of the current
| research. Some of these properties can probably be explained as
| arising from superexchange interactions, but I expect not all of
| them can.
|
| - BSCCO is one of quite a large family of cuprate compounds. In
| this case, it was almost certainly chosen because it cleaves
| easily, producing nice surfaces which are necessary for this type
| of experiment. On the other hand, it is quite structurally
| complicated, and in some sense "messy" compared to many of the
| other commonly-studied compounds. This is actually taken
| advantage of for the experiment discussed here, but it would be
| interesting (if possible) to see if a similar result can be
| replicated in any of the other cuprates.
|
| Anyway, this is quite an interesting experiment, but I'm somewhat
| dissapointed in the Quanta article for such sensationalistic
| reporting. I suppose that's to be expected for a popular science
| article.
|
| [0] https://www.pnas.org/doi/10.1073/pnas.2207449119
| dav_Oz wrote:
| Thanks for your insight.
|
| Most people reading sci-pop articles are by now hopefully used
| to sensationalism.
|
| But I think in this case (which can be equally bad) the
| journalist only spoke to codensed matter physicists biased
| towards or having a stake in the superexchange explanation,
| normally one would at least incorporate one skeptical position
| (such as yours, even if it's a minority one) in yet unsettled
| cases rather than just letting decency speak out of the
| scientists themselves:
|
| > _But Yazdani and other researchers caution that there's still
| a chance, however remote, that glue strength and ease of
| hopping move in lockstep for some other reason, and that the
| field is falling into the classic correlation-equals-causation
| trap. For Yazdani, the real way to prove a causal relationship
| will be to harness superexchange to engineer some flashy new
| superconductors._
| dmitrybrant wrote:
| I assume this is already being done, but I've had the following
| idea kicking around for a while:
|
| Create a simulation, down to the quantum states, of a lattice of
| molecules at a certain simulated temperature (say, room
| temperature), and induce a simulated current through the lattice,
| and see if it superconducts. Proceed by iterating through
| billions of permutations of compounds in the simulated lattice,
| until the simulation finds a room-temperature superconductor.
|
| Assuming this is feasible, does anyone know of organizations that
| are doing this?
| contravariant wrote:
| You can probably find a few condensed matter groups that are
| doing computational simulations, but I think full quantum
| mechanical simulations on that scale are computationally
| intractable so they'll have to use approximations of some sort.
| This is why quantum computers are predicted to exceed the
| computational power of classical computers.
|
| Besides it's been fairly recent that simulations for
| _classical_ thermodynamics with a decent number of particles
| became somewhat feasible. And even then it often uses lots of
| approximations as well as statistical tricks to get decent
| results for sizeable systems. For quantum mechanics quite a few
| tricks to explore the state-space stop working because the
| state-space is unimaginably huge, so I 'm not even sure how to
| begin to do similar simulations, but I reckon they'll be
| _disastrously_ slow for all but the simplest of systems.
|
| The level of detail you need for a simulation that allows you
| to see cooper pairs come into existence is downright insane,
| you might be better of trying to predict next years weather.
| melonrusk wrote:
| As others have pointed out, the computations are currently
| infeasable. The rest of the plan works though, it would just
| need to be done with actual atoms.
| routeroff wrote:
| That is essentially the idea of Random Structure Searching [0],
| but the precision of quantum simulation (better known as ab
| initio) for solids is not perfect and very time consuming.
|
| [0]
| https://iopscience.iop.org/article/10.1088/0953-8984/23/5/05...
| mkhorton wrote:
| Not for superconductivity specifically, but for a broad range
| of properties of crystals, this is what the Materials
| Project[0] does.
|
| Materials Project is funded by the US Department of Energy and
| uses supercomputing to simulate hundreds of thousands of
| different crystal structures on the quantum mechanical level to
| try and find those which have useful properties for practical
| applications.
|
| This line of research is broadly called "materials discovery",
| "materials design" (often "high throughput") or even "materials
| genomics" depending on who you ask. These terms are provided in
| case anyone wants to search and read more about it.
|
| [0] https://materialsproject.org
| fsh wrote:
| The computational complexity of brute-force simulating many-
| body quantum systems scales exponentially in the number of
| particles. There is no supercomputer on earth that can simulate
| a realistic solid.
| aqme28 wrote:
| And you can't get out of this problem by just simulating e.g.
| two or three particles. That small of a system can't simulate
| things like temperature in a meaningful way.
| pouulet wrote:
| This made me think about this nice little TV show:
| https://www.imdb.com/title/tt8134186/
| ncmncm wrote:
| It is anyway a lot easier to simulate a solid that has no
| defects. But many properties found that way turn up in
| defect-ridden, real materials too.
|
| A truly periodic substrate lets you wrap it in a closed
| universe just big enough for what you hope to make live in
| it.
| routeroff wrote:
| It is a very active domain, with lots and lots of techniques
| to do some clever approximations. Brute forcing is not
| feasible, even for the simplest systems.
| helpm33 wrote:
| I don't know the state of the art but I think that we can't
| even predict the static crystal structure of simple substances
| ---e.g. when iron is BCC vs FCC. The first-principles
| simulation of dynamic properties of large quantum many body
| systems is just not feasible. It is possible that this may
| change dramatically when quantum computers arrive---currently
| we describe quantum systems by modeling them with discrete,
| classical computers, and quantum computers might turn out to
| model the relevant quantum processes directly.
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