10 ms·

A New Form of Matter, Excitonium

78 points by jansho 9y ago

QAPereo 9y ago
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.
- bonzini 9y ago
  So is it an insulator, a perfect conductor or a superfluid?...
buovjaga 9y ago
Article at the university's site: https://physics.illinois.edu/news/article/24114 https://physics.illinois.edu/news/article/24114
- Koshkin 9y ago
  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.
- sctb 9y ago
  Thanks! We've updated the link from https://m.phys.org/news/2017-12-physicists-discovery-excitonium.html https://m.phys.org/news/2017-12-physicists-discovery-exciton....
_pferreir_ 9y ago
For a moment I thought it was yet another new ICO. I'm quite happy it's new science instead.
- MadcapJake 9y ago
  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
  - dailyvijeos 9y ago
    BTC can be redeemed for tulip bulbs. ;)
  - deepnotderp 9y ago
    It's a quasi-cryptocurrency!
erikpukinskis 9y ago
I love hearing about macroscopic quantum phenomena. That’s the path to warp drives.
- klodolph 9y ago
  Or more realistically, better sensors.
- dailyvijeos 9y ago
  And improbability drives powered by cheese.
  - vittore 9y ago
    And don't panic.
- ben_w 9y ago
  Hmm. I’m not convinced anything we know about can do what a warp drive needs: https://kitsunesoftware.wordpress.com/2017/04/20/can-a-casimir-cavity-be-used-to-construct-true-negative-mass-metamaterials/ https://kitsunesoftware.wordpress.com/2017/04/20/can-a-casim...
- rytill 9y ago
  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?
  - krapp 9y ago
    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 9y ago
      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.
eximius 9y ago
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)?
- tritium 9y ago
  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.
sebow 9y ago
really excited about this one

78 points by jansho 9y ago

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.

bonzini 9y ago
So is it an insulator, a perfect conductor or a superfluid?...

buovjaga 9y ago

Article at the university's site: https://physics.illinois.edu/news/article/24114 https://physics.illinois.edu/news/article/24114

Koshkin 9y ago
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.
sctb 9y ago
Thanks! We've updated the link from https://m.phys.org/news/2017-12-physicists-discovery-excitonium.html https://m.phys.org/news/2017-12-physicists-discovery-exciton....

_pferreir_ 9y ago

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

MadcapJake 9y ago
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
- dailyvijeos 9y ago
  BTC can be redeemed for tulip bulbs. ;)
- deepnotderp 9y ago
  It's a quasi-cryptocurrency!

erikpukinskis 9y ago

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

klodolph 9y ago
Or more realistically, better sensors.
dailyvijeos 9y ago
And improbability drives powered by cheese.
- vittore 9y ago
  And don't panic.
ben_w 9y ago
Hmm. I’m not convinced anything we know about can do what a warp drive needs: https://kitsunesoftware.wordpress.com/2017/04/20/can-a-casimir-cavity-be-used-to-construct-true-negative-mass-metamaterials/ https://kitsunesoftware.wordpress.com/2017/04/20/can-a-casim...
rytill 9y ago
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?
- krapp 9y ago
  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 9y ago
    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.

eximius 9y ago

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)?

tritium 9y ago
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.

sebow 9y ago

really excited about this one