
A New Form of Matter, Excitonium - jansho
https://physics.illinois.edu/news/article/24114
======
QAPereo
Phys.org is a dumpster fire, and the actual study is interesting.

[http://science.sciencemag.org/content/358/6368/1314](http://science.sciencemag.org/content/358/6368/1314)

 _Excitons—bound states of electrons and holes in solids—are expected to form
a Bose condensate at sufficiently low temperatures. Excitonic condensation has
been studied in systems such as quantum Hall bilayers where physical
separation between electrons and holes enables a longer lifetime for their
bound states. Kogar et al. observed excitons condensing in the three-
dimensional semimetal 1T-TiSe2. In such systems, distinguishing exciton
condensation from other types of order is tricky. To do so, the authors used
momentum-resolved electron energy-loss spectroscopy, a technique developed to
probe electronic collective excitations. The energy needed to excite an
electronic mode became negligible at a finite momentum, signifying the
formation of a condensate._

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bonzini
So is it an insulator, a perfect conductor or a superfluid?...

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_pferreir_
For a moment I thought it was yet another new ICO. I'm quite happy it's new
science instead.

~~~
MadcapJake
Any time a bitcoin transaction takes place, a hole is left in its place. The
hole attracts other coins and when paired with an Ether, a new coin is formed:
ExciteCoin

~~~
deepnotderp
It's a quasi-cryptocurrency!

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erikpukinskis
I love hearing about macroscopic quantum phenomena. That’s the path to warp
drives.

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rytill
I've sort of assumed that warp-drives == time-travel and are thus the same
level of improbability. Is there a consistent universe where we have warp-
drives and are NOT able to time-travel?

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krapp
I Am Not Any Kind Of Physicist, but the way I've always considered it, is that
if you can travel from point A to point B in less time than the speed of light
permits, then that is essentially the same as traveling back in time.

~~~
Simon_says
Well, yea, it literally is traveling back in time in some inertial reference
frame. So far as we know, the laws of physics are identical in one frame, it's
possible in ours.

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eximius
Alright, so it is a particle composed of a particle (an escaped electron) and
the hole (simulation of positive particle = sum of all other electrons
influence) it left in it's valance shell?

If I got that wrong (and possibly even if I got it right), can someone ELI5
this and its applications (if any)?

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tritium
Depends, what does ELI5 mean?

    
    
      When an electron, seated at the edge of a 
      crowded-with-electrons valence band in a 
      semiconductor, gets excited and jumps over 
      the energy gap to the otherwise empty 
      conduction band, it leaves behind a “hole” 
      in the valence band. That hole behaves as 
      though it were a particle with positive 
      charge, and it attracts the escaped 
      electron. When the escaped electron with 
      its negative charge, pairs up with the hole, 
      the two remarkably form a composite particle, 
      a boson.
    

So, it is something else entirely, after this whole process completes. It is
transformed from being an electron, and is no longer an electron.

Electrons are Leptons, not Bosons.

The electron is transformed into a different thing, after it jumps out of its
hole, only to land back in the hole it jumped out of.

When they made an electron jump out of it's valence shell, and then permitted
it to bounce back into the void it left behind, landing back in the slot
changes it enough that it's no longer an electron.

Apparently the orbit it resumes is different enough to be detected with
instrumentation, which actually is pretty interesting, and probably matters in
terms of optimizing materials for solid-state applications.

I can't tell if it's just that these are temporary ripples in the valence
field that eventually resolve themselves, and that it's just a mild
technicality, to be able to notice that the jumping electrons don't
immediately meld back into their cloud, and that on paper, and due to
mathematical descriptions, this "qualifies" the rebounded electron as "no-
longer-an-electron" until it resumes a normal harmonious "orbit" with the
atom's general electron cloud? (AKA: "decays back into an electron" in
technical terms)

How does this kind of boson transition back to an ordinary electron? How long
does that take? How often does this happen in nature? What does this mean in
the grand scheme of things? Is the entire world, nay, _universe_ , slowly and
irrevocably transforming all electrons into these things forever? How come the
all the world's electrons haven't completely decayed into these sorts of
bosons by now? Is this really very significant, or is it just a tidbit of
technical trivia that persists for less than a few units of planck time?

The article does not answer such questions.

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politelemon
ELI5 means "explain like I'm five" or it's a way for asking for a layman's
explanation of something

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buovjaga
Article at the university's site:
[https://physics.illinois.edu/news/article/24114](https://physics.illinois.edu/news/article/24114)

~~~
Koshkin
Most useful link, thanks.

So, the idea seems to be that an electron that has crossed ("excited") into
the conduction band may, instead of recombining with a hole it (or some other
electron) left behind, it may, as the article puts it, "pair up" with the hole
and thus form a bosonic quasi-particle.

One of the interesting aspects of this is that unlike Cooper pairing (of two
electrons), the pairing of an electron with a hole is a collective effect,
i.e. one that requires the participation of many electrons (as well as the
atom's nucleus that accounts for the hole's positive charge).

Those who want to learn more about "collective electrodynamics" may consult a
book by Carver Mead.

