A New Form of Matter, Excitonium
physics.illinois.edu
physics.illinois.edu
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.
I’m not convinced anything we know about can do what a warp drive needs: https://kitsunesoftware.wordpress.com/2017/04/20/can-a-casim...
obviously we have no idea (afaik) how to travel in any other way, but it’s possible that we might discover some new means of transport
If I got that wrong (and possibly even if I got it right), can someone ELI5 this and its applications (if any)?
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.
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.
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.