[HN Gopher] Physicists Create a Bizarre 'Wigner Crystal' Made Pu...
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Physicists Create a Bizarre 'Wigner Crystal' Made Purely of
Electrons
Author : theafh
Score : 93 points
Date : 2021-08-12 14:08 UTC (8 hours ago)
(HTM) web link (www.quantamagazine.org)
(TXT) w3m dump (www.quantamagazine.org)
| mensetmanusman wrote:
| Glad they finally did it!
|
| " Wigner participated in a meeting with Leo Szilard and Albert
| Einstein that resulted in the Einstein-Szilard letter, which
| prompted President Franklin D. Roosevelt to initiate the
| Manhattan Project to develop atomic bombs.
|
| Wigner was afraid that the German nuclear weapon project would
| develop an atomic bomb first. "
| dgs_sgd wrote:
| According to the article scientists have been trying to prove
| this structure for eight decades. Then two _independent_ groups
| report having successfully done it in the same month! What are
| the odds?
| _Microft wrote:
| There are quite a number of similar coincidences in the history
| of science. It seems to me that at some point the necessary
| knowledge or techniques are just there to make some discoveries
| almost inevitable.
|
| https://en.wikipedia.org/wiki/Multiple_discovery
|
| https://en.wikipedia.org/wiki/List_of_multiple_discoveries
| dgs_sgd wrote:
| Yes, they probably relied on the same scientific breakthrough
| where it basically became a race for who could do it first.
| blueprint wrote:
| Well, according to the Hanbury Brown and Twiss effect... more
| than you might expect.
| BenoitP wrote:
| > Past experiments found hints of Wigner crystallization
|
| A member my family actually did his PhD in 1989 on that:
|
| http://www.theses.fr/1989PA066388 (thesis in French, sorry)
|
| The hints were about evidence of shearing transmission displayed
| by the Wigner crystal when poked with some specific RF
| frequencies IIRC.
| marktangotango wrote:
| It'd be cool if these could be made in a material transparent to
| protons, then it'd be a good anode for polywell fusion without
| the energy loss to Bremsstrahlung radiation.
| memling wrote:
| Potential dumb question ahead: how, or does, this relate to the
| Uncertainty Principle? My five-year-old brain says that freezing
| the electrons in a lattice so that they don't move means that
| there's no momentum or velocity, and therefore we should have an
| infinite? uncertainty concerning position.
|
| Obviously something is wrong in my understanding or in the
| precision of the article's discussion. Can someone ELI5?
| gus_massa wrote:
| They are not 100% frozen in a 100% perfect lattice structure.
| They still move a little around the positions where they
| "should" be. Something similar happens with atoms in a normal
| crystal.
| go_elmo wrote:
| maybe even dumber answer ahead: the lattice positions might be
| big enough not to cause any conflict with the uncertainty
| relation?
| zamadatix wrote:
| The distances between electrons in this lattice are enormous
| compared to the electron, even bigger than the typcial
| distances between atoms in a lattice, so being essentially dead
| still in the overall lattice structure doesn't imply much about
| the certainty of the position of the electron at the scale the
| uncertainty principle implies.
| frutiger wrote:
| The uncertainty principle says something different than the
| common understanding.
|
| It says that if you have an ensemble of identically prepared
| systems, the product of variances of non-commuting observables
| obtained by measuring _different instances_ in this ensemble
| will have a lower bound.
| gus_massa wrote:
| Note that this is not a 3D crystal of electrons floating in
| vacuum.
|
| It's a 2D crystal of electrons that live in a thin semiconductor
| that is sandwiched between two layers of other semiconductor. You
| can't pick it with a tiny gripper.
|
| Moreover, I don't understand all the details, but IIUC the
| surrounding semiconductor provides an effective force that makes
| the electrons attract each other when they are not too close. So
| in some sense, the crystal is formed by the electrons, but this
| does not break the expected behavior of a 100% pure negative
| particles in vacuum.
| winter_blue wrote:
| On a slightly different topic: do you think it would
| theoretically be possible to build stable 3D structures
| composed on positrons and electrons (and not have them
| annihilate each other)? I don't really understand the physics
| of why electrons don't collapse into the positive nucleus,
| since positives and negatives should attract, _but I 'm
| wondering if the same interaction keeping protons and electrons
| apart in an atom could come into play with smaller particles
| like electrons and positrons alone_.
| povik wrote:
| > I don't really understand the physics of why electrons
| don't collapse into the positive nucleus, since positives and
| negatives should attract
|
| My (student of physics) answer to that would be that they are
| pretty much collapsed as much as they can. It's just that
| under quantum mechanics that least energetic state is not the
| one in which the electron is perfectly co-localized with the
| positive charge. (As that perfect co-localization is not even
| physically attainable.)
| IntrepidWorm wrote:
| > On a slightly different topic: I don't really understand
| the physics of why electrons don't collapse into the positive
| nucleus, since positives and negatives should attract.
|
| Good question- this was a clear and troubling problem in the
| classical atomic models before quantum mechanics. Thinking of
| electrons as little balls whizzing around, being attracted
| and repelled by various field forces does seem to lend itself
| to this question.
|
| The current understanding is that since electrons are quantum
| particles, they can only gain or lose energy through
| quantized packets, and can only occupy certain energy states.
| In fact, it's much more accurate to describe electrons by
| their probability fields, and not as those little balls.
| Quantum mechanics then describes probability shells called
| Sommerfeld orbits, where the chance of finding an electron at
| any given point peaks. Unless energy is added or removed from
| the system by those aformentioned quantized packets,
| electrons tend to remain at their respective energy levels
| and shells.
| wcoenen wrote:
| > _The current understanding is that since electrons are
| quantum particles, they can only gain or lose energy
| through quantized packets_
|
| Just to clarify. An electron moving freely through a vacuum
| can move at any speed; it is not restricted to certain
| energy levels. (Speed and therefore kinetic energy is
| relative to the reference frame anyway.)
|
| The quantization of energy comes into play when the
| electron is spatially confined in some system. This is
| related to the wave behavior of the particle, and because
| energy is related to wavelength. Much like how a standing
| wave on a string can only have wavelengths such that an
| integer multiple of them fit on the string.
| IntrepidWorm wrote:
| Good clarification- my wording was clunky.
| foobarian wrote:
| I was confused by not seeing an explanation of where the
| attraction comes from (there shouldn't be any). Sounds like the
| top and bottom layers push the electrons together and the
| electrons settle into a hexagonal grid like a flat arrangement
| of balls would.
|
| To me being able to measure/observe a thing like this is a
| whole other level of amazing.
| gus_massa wrote:
| It's too far from my area to be sure, but let's guess ...
|
| Perhaps it similar to the Cooper pair effect. In this effect,
| it looks like electrons inside a conductor attract each
| other. From https://en.wikipedia.org/wiki/Cooper_pair
|
| > _Although Cooper pairing is a quantum effect, the reason
| for the pairing can be seen from a simplified classical
| explanation. An electron in a metal normally behaves as a
| free particle. The electron is repelled from other electrons
| due to their negative charge, but it also attracts the
| positive ions that make up the rigid lattice of the metal.
| This attraction distorts the ion lattice, moving the ions
| slightly toward the electron, increasing the positive charge
| density of the lattice in the vicinity. This positive charge
| can attract other electrons. At long distances, this
| attraction between electrons due to the displaced ions can
| overcome the electrons ' repulsion due to their negative
| charge, and cause them to pair up. The rigorous quantum
| mechanical explanation shows that the effect is due to
| electron-phonon interactions, with the phonon being the
| collective motion of the positively-charged lattice._
|
| This attraction is too small and is only important when the
| temperature is very low, and is the explanation of low
| temperature superconductivity.
|
| <guess> So perhaps there is a Cooper-pair-like effect here,
| that creates the illusion that the electrons attract each
| other. They are using semiconductors, so perhaps it's caused
| not by the movement of the nuclei, but the movement of the
| holes in the other semiconductor.</guess>
| selimthegrim wrote:
| Wigner crystals have been well known in theory since the 1930s,
| there's nothing bizarre about them.
| IndianaBones wrote:
| Some Indiana Jones bullshit! wow!!!
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