High Temperature Bose-Einstein Condensation Observed 106
ultracool writes "Two separate research groups claim to have observed Bose-Einstein condensation (BEC) in quasiparticles at much higher temperatures than atomic BEC — one at 19 Kelvin and the other at room temperature. The 19 K BEC was composed of half-matter, half-light quasi-particles called polaritons, and the room temperature condensate was composed of 'magnons' (packets of magnetic energy). There is some skepticism among physicists as to whether these really are BECs. If they are true BECs, these experiments are the first evidence of them in the solid state." Just in case you need a brush up on BEC, like I did, check out the Wikipedia article on Bose-Einstein condensation.
Can't Be (Score:4, Funny)
You know how the saying goes - "No highs, no lows, gotta be Bose!"
Oh wait, that's a different kind of Bose.
Nevermind.
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As much as I'm gonna get marked off-topic for this ... to those of us who don't have 'golden ears', Bose speakers sound just fine. I rather like my set of four 201's which makes the basis for my AV system.
They never claimed to sell the speakers with the greatest degree of fidelity, they claim to sell speakers that sound good to the majority of l
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Actually, when he said "No highs, no lows, must be Bose" he was specifically talking about Bose speakers and making a joke. (Bose speakers shift things to the mid-range.)
Maybe you missed the part where he said "Oh, different Bose".
I know that Bose speakers has nothing to do with BEC, but the OP injected a funny, which did refer to Bose speakers. Which is what I responded to.
Cheers
Solid State? (Score:4, Insightful)
Re:Solid State? (Score:5, Informative)
Good question. And damn hard to explain in terms that don't sound insane to the layman
Thing is, the condensed particles here aren't the particles that make up the solid. They're not quite real particles, even. They're so-called quasiparticles, which are a fancy way condensed-matter physicists have of describing what the rest of us call "interactions". Each interaction has its own kind of quasiparticle, (and some silly name ending with -on) and they're basically described just like real particles are. The trick is you can describe the system in terms of these virtual particles instead of the real ones and simplify the problem.
To give an analogy, you could think about a bubble moving through some liquid. The bubble isn't actually a real particle - it's just the overall effect of a bunch of gas molecules pressing and bouncing against the liquid molecules. But thinking of it as just a "bubble particle" is a lot simpler.
Anyway. So the condensate here isn't made up of the solid's atoms. It's made up of quasiparticles. And this is why there's some debate on whether this should be called a BEC or not. On one hand, they can, and do have coherence here. On the other hand, they're just not really real!
But it's also pointed out they're extremely short-lived. It's indeed questionable if you can call something a BEC if it's short-lived, because a BEC is supposedly a low and stable state. (So the question becomes "How stable should it be to be a BEC?") But regardless of that, it's no less interesting.
My guess is, people will probably continue to call every BEC-like kind of condensate a BEC. When the need arises to distinguish the two, they'll have to invent a new term for that context, like "quasiparticle condensate" or something.
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I parse that as "we're making shit up, then condense that into something real, at room temperature." :-)
Seriously, I had no idea Slashdot articles could be this far above my head.
Slashdot used to be more technical like that (Score:2, Insightful)
Slashdot started off as a strongly science/tech-oriented discussion site, and articles that required detailed knowledge of the subject matter were common in those early days (I have a 4-digit Slashdot ID so this is first-hand).
But popularity brought in a broader cross-section of the population, and deep science and engineering knowledge is rare in the population at large. The fact that nowadays the majority of Slashdot articles are
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Normal matter, including every BEC I have heard
of is made of atoms, which are quantum particles.
However solids, like every other kind of matter
(even BECs!) support excitations, which can
also be quantum particles (or quasi-particles).
It seems that they have made a BEC out
of the quasi particles in in a solid (which
is not itself a BEC).
Re:Solid State? (Score:5, Informative)
You can think about it in a coneptually-easier way by thinking about vibrations, which is more intuitive. The simplest model in which to think about vibrations would be in one dimension. Imagine you have a collection of some equal masses, equally spaced, with equal springs between each of those masses. If you excite the system anwhere (ie, push some of the masses), it will vibrate throughout the whole system because each 'atom' is coupled through the springs. The individual excitations of such a system would be the collective 'modes' of oscillation of the system. A mode is a specific oscillation that once set up will continue uninterrupted (without friction). For a simple one-dimensional system like the modes would be a sinusoidal oscillations of the system, where the wavelength of each mode would be the twice the length of the 'crystal' divided by an integer. See the wiki page on the Normal Mode [wikipedia.org] with a cute animation.
You can extend this to three-dimensions by considering a three-dimensional grid of massive atoms, connected by springs. Real crystals don't have to be cubic, they can have a number of various arrangements (hexagonal, trigonal, diamond structure), and the effective spring constants can be different in different directions. But N masses, in 3 dimensions, will have 3N distinct modes. What's important to see is that each mode would have its own frequency, and wavelength, and typically the speed of propagation of each mode doesn't have to be the same. Also of note is that each mode has its own energy.
If you now consider a real crystal, and apply these same concepts but within the realm of quantum mechanics, you get a similar result, but each 'mode' now becomes a 'quanta' of lattice vibration. These vibration quanta are called phonons [wikipedia.org], which are bosons (they have spin 0, and bosons have integer spin). Even a small chunk of crystal will have on the order 10E23 atoms, so this is a huge number of allowed quantizations, and they can be thought of as a continuum. Each allowed 'mode' will again have its own frequency, wavelength, and energy. If you have a chunk of crystal at any non-zero temperature, any of the modes above the ground state (the ground state is the mode with the lowest allowed energy) can be 'occupied' with a finite probability. As you approach zero temperature, the probability of any mode above the ground state being occupied approaches zero.
A Bose-Einstein Condensate refers to an effective phase transition that happens as you cool the system and it becomes harder to excite the higher energy states as system becomes highly occupied in the ground state. There is a phase transition, the presence of which can be manifested by different qualities in things like specific heat, magnetization, magnetic susceptibility, etc. The crystal is still a solid crystal per-se (meaning it has a well-defined atomic ordering) but the occupations of the various modes of the system will drastically change, building into a near divergence at the ground state.
In the 'magnon' case as mentioned in TFA, you can think of it like phonons described above, but instead of two atoms exchanging vibrational energy, they are exchanging magnetic energy. Each electron is a spin-1/2 dipole (a fermion, not a boson), and there are interactions between two neighboring spins. Spin interactions are highly model dependent, meaning the types of atoms and shape of the crystal has huge impact on the interactions, which is why some materials are magnetic and some are non-magnetic. If you quantize the magnetic interactions you get spin-waves [wikipedia.org] or magnons, similar to the sine-wave vibrational modes of the lattice above except the direction of the spin-moment changes instead of the atom displacement in the lattice.
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Re:Solid State? (Score:5, Informative)
A mode is the collective motion of the atoms in the crystal, not a single frequency. A mode will oscillate at a specific frequency, however. If you write the 'equations of motion' for all atoms in the crystal in 'matrix' form, the modes would correspond to the 'eigenvalues' of that matrix. I'm sure these sentence will confuse you, but again, I can't boil linear algebra anad its application to mechanics down into a few understandable sentences to be comprehended in only a few minutes. f I tried to go too basic into all the details that post would evolveee into a textbook sized tome.
So a crystal will have several different modes. This is very much like quantum mechanics, where energy states are quantized, and each so-called 'eigenstate' has a specific 'wavefunction' associated with it. These oscillatory modes are called 'phonons', which are 'bosons'. The 'magnons' referred to in the articles are different modes. In those cases it's not vibrations they're 'quantizing' but magnetic interactions. The electrons on the atoms in the lattice are tiny 'magnetic dipoles', which can rotate, interact with magnetic fields, interact with other nearby electrons, etc. Again, if this paragraph confuses you then look up the terms in quotes.
Correction (Score:2)
Eigenvalues are scalars, eigenvectors are vectors. In this case the eigenvectors would describe the motion of each of the atoms in the crystal.
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Dude... I was so out of my depth, you could have said "the modes would correspond to the 'Keanuvectors' of the Matrix" and I would have been like, "Woah".
Seriously, though -- like the other non-troll respondents to your mess
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Unacceptable! I'm sure the AC who was complaining about unfamiliar words like "crystal" could write a similar length article on some easy technical topic, like how to write a C compiler, without using technical terms like 'bit' or 'keyboard' that might confuse...
Seriously, thanks for the explanation - some of us appreciate it when a professional in a field takes the time to
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Although for future lecturing reference, you kinda lost me when we moved onto real crystals. But that may just have been the innate complexity of the subject matter.
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Radioactive decay does affect a BEC. Firstly, it frees energy that will heat the BEC. A BEC of atoms is so cold that even recoils from (ordinary light) photons destroys it, then imaging what the recoils from the decay would do. Secondly, a BEC can only consist of identical particles. Emitting a alpha or beta particle leaves you with an other species and this can no longer be part of the BEC.
I am a Ph.D. student actually working with B
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Identical means the same isotope and same charge. Also only neutral atoms since any charge would make it very hard to achieve the density needed to achieve BEC (ions repel each other, you know). I don't think there is any BEC with ions.
Mostly alkali atoms have been used (the ones leftmost in the periodic table). These are the ones most straightforward to c
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Seriously though, your explanation is a lot easier to understand than Kittel's.
Re:Solid State? Good Info (Score:1)
Just think about *this* (Score:1, Offtopic)
Solid state? (Score:3, Informative)
Ryan Fenton
A *live* Wikipedia page? Thanks guys. Nice work. (Score:4, Insightful)
Editors, if you link a Wikipedia page from the summary, PLEASE link a historical revision. That way, whatever vandalism happens won't affect the link, and thus fewer people will be tempted to even vandalize at all.
Seriously, do the editors have any sense at all? It's not like this is a new problem.
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Wait, what?
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So Star Trek was right... (Score:2, Funny)
Re:So Star Trek was right... (Score:4, Funny)
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It's like filling a ballon until it pops!
Hey baby... like my shiny Commander's pips?
Can anyone read the articles. (Score:2, Interesting)
The main thing I am wondering about is dimensionality. I've seen
lectures before where people have come up with pancake like-systems
that are *like* BECs at 1 Kelvin, but unfortunately you can't meet the
pedantic requirements for BEC in less than 3d.
But if these systems are 3d, then it seems reasonable. We are talking
about quasi-particles here. As one of these abstracts says, their
(effective) mass is much less than that of an atom, therefore for
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I haven't delved into the details, but the latter one seems to have a much higher lifetime as well, and I guess is the more proper BEC of the two. I presume it's the more interesting result, since as you say (and the references indicate) the 2d-quasiparticle-condensate thing has been done before.
(Since it's not my field, don't put too much faith in my impressions of what seesm to be 'interesting'. For all I know, this could be undergrad-level condensed-matter ph
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Well the bit about disorder is prossibly a triumph of hope over experience, but they are right about the finite system size. They say 2-d systems can't
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It is indeed, at least I did learn about it in an undergraduate course on statistical physics.
However, one of the authors of the first claimed that what they created was a proper BEC as well since it was finite. He claimed it was only impossible to have infinite two dimensional BECs. I don't have any idea as to the validity of this claim though.
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The thing I love about science... (Score:3, Funny)
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huh (Score:2, Interesting)
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They cool thing about BEC is that it violates that intuition. Until B&E published, everyone thought that "much higher than zero kelvin" meant when that (in the appropriate units) the temperature (i.e. roughly the average energy per particle) had to be (much) less than the difference in energy between lowest state and any of the the others. If you think about this assumption, you will see that it nearly comes from
Bolzman's law (and if you don't know what Boltzman's law is, and a
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Wow (Score:4, Funny)
This statement caused my bogometer to break. Now the needle is stuck all the way right at WTF.
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Look at that, that's all one sentence, isn't it?
More like O'Neil. (Score:3, Funny)
Oneil: "Magnets."
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I do! I do! I think they're controlled by a series of really big magnets buried under the Earth's crust.
You're an ignorant dolt, Max.
Yes, I really am dumb. (Score:1)
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quanta: packets of things that are quantized, like, you know, everything that happens at the atomic scale
magnetic excitations: increase in magnetic energy, for example by periodically flipping the moment like an oscillator
magnetically ordered: lined up
ensemble: group of stuff
magnetic moments: little tiny magnets formed by the ele
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Ok, since your "bogometer" seems to go off at one of the most highly respected scientific publications, on the planet... let me do a little physics-to-layman translation for ya.
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yeah, yeah, yeah. I get it... it's a nerd jerk off magazine. It all becomes more and more trekish every year.
Ding Dong! (Score:1)
You have used up your stockpile of confounding-words-that-begin-with-an-M today! Please come again!
What 'chu talking about WIllis? (Score:3, Funny)
Bah real physicists start the day with a nice large glass of Bose-Einstein Condensate (Now with Calcium)
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What? (Score:1)
Please translate. (Score:3, Insightful)
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It depends on what you find important, remember most physics is a lot less practical than most biology. In my view people are interested in BEC because it is one of the few systems in whic
Why does everybody think a hole is a particle? (Score:1)
So this "Polarion" is said to be an electron-hole pair. You know what an electron + a lack of an electron is? AN ELECTRON. Oy.... Every time I bring this up, some other EE (yes, I am an EE) always says that, yes a hole c
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Re:Why does everybody think a hole is a particle? (Score:4, Informative)
You say you're an EE, but it seems apparent have you taken any solid-state physics classes yet. That's where you'll see the real utility in talking about holes. When you look at the band structure in the vicinity of an energy gap, from the quantum-mechanical point of view, excitations above the ground zero-temperature state are most easily expressable in terms of electron-occupations and hole occupations.
For example, in a direct-gap semiconductor, at zero temperature the valence band is fully occupied, and the conduction band is fully unoccupied. If you consider this system at finite temperatures, states in the conduction band can be occupied with finite probability, provided that a corresponding momentum-conserving state in the valence band becomes unoccupied. So sure, you can always write the ground state as the sum of all occupied states up to the fermi energy (the Fermi sea), but this gets mathematically very cumbersome. Especially for complicated materials with anisotropic band structures, etc.
It makes much more sense to redefine the ground state (the filled fermi sea) as being the vacuum state (ie, no occupations). Mathematically this makes calculations MUCH easier, as then an excitation will consist of exciting BOTH an electron (in the conduction band) and a hole (forcing a vacancy in the fermi sea). This is highly necessary for making calculations (such as conductivity, magnetization, specific heat, etc) actually possible to do. Now when you consider momentum and spin-dependent phenomena (magnetism, superconductivity, spintronics, etc) you have to carefully consider the excitations of the hole (what is it's momentum and spin). So yes, holes do map exactly to quasiparticles.
When you finally take some solid-state courses you'll see that holes DO HAVE an an effective mass (quite often not the same as the mass of the electron). They also have charge (-e), momentum, energy, and spin. Now regarding the polarons, if you're talking about complex quantum interactions, since any excitation into the conduction band requires similar 'excitation' of a hole, there is no reason to assume these two will act independently, they are of course highly coupled (conserving total momentum, spin, etc). In fact, creation of a particle-hole pair are somtimes called excitons [wikipedia.org]. Now in the BEC systems under study, what reasons do you have a priori to assume that such quantized excitations would NOT consist of particle-hole pairs?
The concept of your post implies that you are intuitively understanding holes only as the lack of the electrons in a classical system. But when you consider the microscopic interactions with proper accounting for quantum mechanics and thermodynamics, your classical view falls far short of being feasibly workable. It becomes much MUCH MUCH easier to talk about holes as excitations of the Fermi sea.
And on one final note that's outside my element, by considering holes as excitations of the Fermi sea, Dirac made similar propositions in the burgeoning field of quantum-electrodynamics to propose the existence of a similar anti-electron (to the vacuum ground state being like the Fermi sea) which is the positron.
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So I understand the first part of your post was backing one of my points, that it is an
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I read up a bit more on the excitons and quasiparticles. Quasiparticles are abstactions of particles, it seems. They don't actually exist but make calculations much easier, so I calculated what happens with the quasiparticle, and figure out how the rest of the particles around it are affected, as opposed to figuring out what is going on with each individual other particle around it.
That's all well and good, but that is still an abstraction of a particle, not a particle. It's an idea that exp
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I shot my... (Score:1, Offtopic)
No, the cat does not "got my tongue." (Score:1)
Ok, IANAP, but I thought the BEC was the result of supercooling atoms until their temperature, and hence momentum, was virtually 0. Because of quantum conjugate pairs, their position's uncertainty therefore must skyrocket. This bizarre, near-macroscopic "thing" was the "condensate". That Wikipedia article mentions none of this. Am I even more clueless than I already know I am, or is th
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Are you sure you are reading from the correct encyclopedia? You should probably check the article on uncyclopedia to be sure....
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Anyway, thanks for having me, dinner was marvelous, we should do this again sometime...
hugs & kisses & hearts & flowers,
~ken
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The Number of Elephants Has Tripled! [wikipedia.org].
Re:The Wiki article (Score:4, Informative)
Dear Wikipedia fanboys,
Learn to fucking reference it right. When you make a link to it, include the full link to the timestamp of the state it is in when you read it.
Example: http://en.wikipedia.org/w/index.php?title=Bose%E2
would have been the correct way to reference Wikipwdia for the grandparent wiki fanboy.
That way, while the content may or may not be either excellent material written by an expert on the field, or the ramplings of a moronic 12-year-old who felt like he knew how things 'work' better than the Ph.D. in the field whose entry he just erased, at least you know the reader will be looking at the same content you did.
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