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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.
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High Temperature Bose-Einstein Condensation Observed

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  • Can't Be (Score:4, Funny)

    by Jah-Wren Ryel ( 80510 ) on Friday September 29, 2006 @10:50PM (#16255595)
    A high-temperature Bose-Einstein condensate? It can't be.
    You know how the saying goes - "No highs, no lows, gotta be Bose!"

    Oh wait, that's a different kind of Bose.

    Nevermind.
    • by hachete ( 473378 )
      It was Bose-Eisenstein, all the way down the steps.
    • A high-temperature Bose-Einstein condensate? It can't be.
      You know how the saying goes - "No highs, no lows, gotta be Bose!"

      Oh wait, that's a different kind of Bose.

      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

  • Solid State? (Score:4, Insightful)

    by FlavorText ( 999057 ) on Friday September 29, 2006 @10:58PM (#16255653)
    I thought Bose-Einstein condensate was a completely different state of matter. How then, could it appear in a "solid state"?
    • Re:Solid State? (Score:5, Informative)

      by k98sven ( 324383 ) on Friday September 29, 2006 @11:44PM (#16255823) Journal
      I thought Bose-Einstein condensate was a completely different state of matter. How then, could it appear in a "solid state"?

      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.
      • 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.

        • by Anonymous Coward
          Seriously, I had no idea Slashdot articles could be this far above my head.

          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
          • by Engine ( 86689 )
            Maybe, and maybe hopefully, slashdot will be like that again when more of the common people move over to sites like digg. I absolutly do not mind them being here, there is a lot of subjects discuss here about things that I am far from an expert in. I would not mind if the discussions were on a slightly higher level. If the submissions are a little bit above my head, I learn more from the following discussions and gain from the huge amount of collected knowledge in the slash-community. The knowledgeable peop
      • Re: (Score:3, Interesting)

        by doug363 ( 256267 )
        On the question of whether a BEC made of quasiparticles is really a BEC: a laser beam fits (some) definitions of a BEC of photons, but most physicists don't immediately think laser beams when someone talks about BECs. I'd think that these "BECs" would be considered in the same way: technially a BEC perhaps, but not the definitive example of one. After all, the quasiparticles are just quantized vibrational modes of non-EM fields.
    • by raka ( 17481 )
      The bit about "solid state" was almost B.S.

      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)

      by wass ( 72082 ) on Saturday September 30, 2006 @01:12AM (#16256189)
      Let me attempt a hopefully-understandable explanation. I'm a graduate student in experimental condensed-matter physics.

      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.
      • Re: (Score:3, Funny)

        by Anonymous Coward
        It's good to see that I'm not the only super-genius here.
      • Re: (Score:1, Insightful)

        by Anonymous Coward
        No offense, but that explanation is almost entirely incomprehensible. It introduces unfamiliar terms ("crystal," "effective spring constants," "effective phase transition," etc.) with no context from which to infer their meaning, and uses words in ambiguous ways (for example, it took me a while to understand that a "mode" describes not a single back-and-forth motion, but rather a specific frequency of motion). Additionally, it provides no assistance in making significant conceptual leaps, such as the one fr
        • Re:Solid State? (Score:5, Informative)

          by wass ( 72082 ) on Saturday September 30, 2006 @10:24AM (#16258287)
          Sorry that I'm unable to boil all of quantum mechanics and solid-state physics into a single easily-comprehensible slashdot posting, while spending a maximum of 15 minutes writing it. I included a few mentions to wikipedia (eg on modes) to aid you, and also quoted certain terms for you to look up on your own. Any quoted terms below, please look up yourself if you don't understand. This post can hopefully get you started. But I can't believe I'm being criticized for spending my own time trying to help someone entirely unfamiliar with the field understand something.

          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.
          • Oops, seemingly-minor correction, but in the 2nd paragraph I should have said : "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 'eigenvectors' of that matrix."

            Eigenvalues are scalars, eigenvectors are vectors. In this case the eigenvectors would describe the motion of each of the atoms in the crystal.
            • Oops, seemingly-minor correction, but in the 2nd paragraph I should have said : "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 'eigenvectors' of that matrix."

              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
          • by SimplyI ( 974376 )
            Thanks for your post. It was articulate and informative. I had only ever known wikipedia's less in-depth explanation. It's unfortuneate assholes exist, yes. I guess since you offered a bit of an explanation he decided it was your duty to teach him everything you know. Oh well.
          • Sorry that I'm unable to boil all of quantum mechanics and solid-state physics into a single easily-comprehensible slashdot posting

            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

        • I think that rather than blaming the teacher you should blame your own lack of comprehension skills. My personal background in Physics doesn't extend much past that of a sophomore Physics undergrad, though I do have a strong background in math, and I thought that his post was entirely understandable and very eye-opening for me as to how all this stuff works, and what the research in TFA was trying to do.
      • by Gulthek ( 12570 )
        Awesome comment, thanks!

        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.
      • Re: (Score:3, Interesting)

        by cybrpnk2 ( 579066 )
        Perhaps you can answer (or speculate about) a question I've always wondered about concerning BECs. Say you create a BEC from radioactive atoms and you keep it cooled down for several half-lives of whatever element isotope you've used. What happens? Does being in a BEC halt radioactive decay? Does radioactive decay affect a BEC during its existence? Will the decay products pop out when the BEC warms?
        • Re: (Score:3, Insightful)

          by Engine ( 86689 )
          Being in a BEC does not halt radioactive decay. I don't see why it should.

          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
      • Re: (Score:2, Funny)

        by kickdown ( 824054 )
        I'm scared.
      • You talk purdier than a two dollar whore.

        Seriously though, your explanation is a lot easier to understand than Kittel's.
      • I really appreciated the information. My dad always taught me to hang out with people smarter than me, because that would make me smarter in the long run. He taught me to never be afraid to "look something up". That's probably why people understand what I say just about as much as people understand your topic. It was great information, and I followed it well. Glad to have you on board.
  • In the time it took you to read that Wikipedia article, David Banh wrote and published a groundbreaking paper on the subject.
  • Solid state? (Score:3, Informative)

    by RyanFenton ( 230700 ) on Friday September 29, 2006 @11:11PM (#16255729)
    How can a mishmash of atoms collapsed into the same space (b-e condensate) have a 'solid state'? Their radius' overlap. Is this more like a gas freezing without any other transition?

    Ryan Fenton
  • by NereusRen ( 811533 ) on Friday September 29, 2006 @11:24PM (#16255757)
    Oh, for the love of...

    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.
    • Re: (Score:3, Insightful)

      And whatever corrections are made won't be updated in the link, either. With many eyes, after all, all errors are shallow--isn't that the founding principle of Wikipedia? A crush of visitors should improve the article beyond anything seen in Britannica or the New York Post.

      Wait, what?
  • by Anonymous Coward
    But can you reverse the angular momentum of polaritrons in order to counteract a magneton beam?
  • Unfortunately I'm at home, so I can't read the actual articles.
    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
    • Re: (Score:2, Interesting)

      by k98sven ( 324383 )
      Kasprzak et al. is 2d, Demokritov et al is 3d.

      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
      • by raka ( 17481 )
        You are probably right, but ... Deveaud-Plédran happily dismisses both assertions. "BEC is forbidden only in two dimensions for an infinite system without disorder. We have a finite system with disorder, so standard BEC is allowed. And despite the quasiparticle nature and very short lifetime, we have shown that we are able to get a thermal equilibrium."

        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
      • 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.

    • by Yehooti ( 816574 )
      Certainly the math escapes me after so many years but I think that the chronos sinclastic infindubula theorms cover this nicely. Clark covered this nicely in the early '70's.
  • huh (Score:2, Interesting)

    by sydres ( 656690 )
    I always assumed probably wrongly that a B-E condensate was when groups of atoms dropped to an energy state that allowed them to act like one very large and coordinated atom. Would not thermodynamics keep in a system like a B-E this organization from occurring at temps that much higher than zero kelvin, forces like vanderwahls and electro weak forces. or if some physisististist care to enlighten a mathematical wannabee
    • Re: (Score:3, Insightful)

      by raka ( 17481 )
      You intuation is right.

      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
      • by sydres ( 656690 )
        so its almost like when electrons become stimulated in a laser they all jump to pretty much identical states and act like a coherent population, or at least till one drops back causing all to follow suit, only in a B-E its that they give up energy to act as a "population" and its not just electrons doing this. At least that is how I am envisioning it, thanks for enlightening
  • Wow (Score:4, Funny)

    by SpacePunk ( 17960 ) on Saturday September 30, 2006 @12:01AM (#16255899) Homepage
    "Magnons are the quanta of magnetic excitations in a magnetically ordered ensemble of magnetic moments."

    This statement caused my bogometer to break. Now the needle is stuck all the way right at WTF.
    • Re: (Score:1, Funny)

      by samurphy21 ( 193736 )
      This feels like an episode of Stargate SG-1 where Carter says something technical to explain a wormhole phenomenon, and all the military guys start looking at each other like monkeys looking for poop to fling while I'm yelling at the screen in frustration because whatever she said, while sci-fi-ish in its veracity wasn't as hard to follow as the writers tried to make it seem.

      Look at that, that's all one sentence, isn't it?
      • by raka ( 17481 )
        Carter: "Well how do *you* think it's done".

        Oneil: "Magnets."
        • by KDR_11k ( 778916 )
          Who knows what makes these inanimate objects dance their infernal jitterbug?

          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.
    • Re: (Score:3, Informative)

      by MustardMan ( 52102 )
      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.

      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
      • Re: (Score:1, Flamebait)

        by SpacePunk ( 17960 )
        ------------------
        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.
        -------------------

        yeah, yeah, yeah. I get it... it's a nerd jerk off magazine. It all becomes more and more trekish every year.
    • "Magnons are the quanta of magnetic excitations in a magnetically ordered ensemble of magnetic moments."

      You have used up your stockpile of confounding-words-that-begin-with-an-M today! Please come again!
  • by OverlordQ ( 264228 ) on Saturday September 30, 2006 @12:09AM (#16255939) Journal
    If they are true BECs, these experiments are the first evidence of them in the solid state.

    Bah real physicists start the day with a nice large glass of Bose-Einstein Condensate (Now with Calcium)
  • Someone understood that?
  • Please translate. (Score:3, Insightful)

    by posterlogo ( 943853 ) on Saturday September 30, 2006 @02:44AM (#16256501)
    I have a Ph.D. in biology, and I am interested in current research in many other fields as well. That said, I have no idea WTF the *significance* of the current breakthrough is. What does it mean? Why isn't there even a one sentence half-assed attempt in the summary? Thanks for the wiki-link. If I wanted to seriously brush up while trying to navigate the ridiculous wiki, I'd go there. Seriously, most people might just want to know why they should give a shit that BE condensation has been observed at solid-state. Don't get me wrong, I think there is something fascinating in all this, just wish the summary would have pointed to that aspect instead of regurgitating the so-called claimes of a breakthrough.
    • How about you RTFA? "What practical applications will this lead to? "We are still exploring the basic physics of this phenomenon," says Deveaud. "But just achieving this phase in the solid state is exciting. In the mid 1900s, transistors replaced vacuum lamps, and now most useful devices are made in the solid state," he explains. "Polaritons, although made with a photon, are really quasi-particles in the solid. It is likely that they can be manipulated much as electrons are -- an advance that has led to in
    • Re: (Score:3, Interesting)

      by raka ( 17481 )
      Seriously, most people might just want to know why they should give a shit that BE condensation has been observed at solid-state. Don't get me wrong, I think there is something fascinating in all this, just wish the summary would have pointed to that aspect instead of regurgitating the so-called claimes of a breakthrough.

      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
  • I am getting so sick of hearing people talk about a hole as if it was a particle. A hole, at least in the semiconductor sense, is where an electron should be in a valence crystaline lattice (I know I'm saying it badly, but if you know what I'm talking about, you'll know what I meant).

    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
    • by wass ( 72082 ) on Saturday September 30, 2006 @11:36AM (#16258755)
      I am getting so sick of hearing people talk about a hole as if it was a particle.[snip] I just don't understand how they call something an electron-hole pair, and say that it isn't just an electron.

      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.

      • Thank you Wass, for the very well thought out, and researched (or at least known from previous study) post about this. I am only a senior at college for a BS in EE, so I definitely don't know everything about it yet. As far as I've been told, holes were just an abstraction of a lack of an electron in the valence band, and used (at best) as a convinience in doing calculations dealing with semi-conductors and the like.

        So I understand the first part of your post was backing one of my points, that it is an
        • Re: (Score:3, Informative)

          by wass ( 72082 )
          It's not as useful think about the electron's or hole's location, but much more useful to talk about its momentum (or other useful 'good quantum number'). If you think of the electrons as a gas, without strong interactions between each other, they form a a continum of states, each state has momentum (hbar*k) and energy (p^2/2m) where k is the wavevector, which is quantized as a function of your sample's size. (you hopefully recognize that expression as the kinetic energy, where we're assuming the lattice
      • Addendum:
        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
    • I am getting so sick of hearing people talk about a hole as if it was a particle. A hole, at least in the semiconductor sense, is where an electron should be in a valence crystaline lattice (I know I'm saying it badly, but if you know what I'm talking about, you'll know what I meant). 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 can mo

    • by bodan ( 619290 )
      I'm not much above you in my understanding of these things, but there is in the comments above a very good (easy to visualize) analogy to the "electron hole" idea: bubbles in a liquid. They're all really places where there is no liquid, but it's still easier to think of them as "particles". They can move in the liquid, they have a sort of "negative mass" because they float to the surface in a gravity field, unlike something with positive mass that falls (it's all relative to the system you're looking at, so
  • I shot my... (Score:1, Offtopic)

    ...Bose-Einstein Condensate all over her face. Boy, was she cold after!
  • > Just in case you need a brush up on BEC, like I did, check out the Wikipedia article on Bose-Einstein condensation [wikipedia.org]

    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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