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High Temperature Bose-Einstein Condensation Observed
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.
You could have tried the external links at the end of the page.
"I just can't sit while people are saying nonsense in a meeting without saying it's nonsense" J Watson, Sci Am 288:(4)51
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.
When information is power, privacy is freedom.
I thought Bose-Einstein condensate was a completely different state of matter. How then, could it appear in a "solid state"?
"Yes, I do have something to hide - my shame."
Yeah, because nobody can edit external links on Wikipedia articles.
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
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.
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 they
can have much higher energies than atoms of similar momentum. Because
BEC is all about getting (the uncertainty of) momentum * (uncertainty of)
position down below a magic number, it seems reasonable.
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?
And now, a PSA from David Lynch.
Even better, the idiots who insist on using as a reference a website any 12-year-old can change whenever he feels like it could at least learn to use it right.
% 80%93Einstein_condensate&diff=78635928&oldid=78633 658
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.
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
"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.
Steve's Computer Service, Hobbs, NM
And now, a PSA from David Lynch.
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)
Your hair look like poop, Bob! - Wanker.
Carter: "Well how do *you* think it's done".
Oneil: "Magnets."
"We gave the word mob a bad name!"
it's the only way to lose an English major in an English sentence.
The role of the writer is not to say what we can all say, but what we are unable to say. -Anais Nin
The site make it very easy to pick a version of a page to link. The left side of the page say cite this article. Click it and use the link it provides.
You mad
For people who still don't understand anything of it, there is a very good article here about Bose-Einstein. Even some nice applets to play with sliders to see how it all works.
To repeat what others have said, requires education, to challenge it , requires brains.
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.
Is that the beer he used the chisel on?
Justice is the sheep getting arrested while an impartial judge declares the vote void.
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 merely rehashes of some non-technical person's blog is just the editors keeping in tune with their majority audience. It's sad, but inevitable.
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. 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.
make world, not war
In a 3-D crystal, your momentum is a 3-D vector, and therefore 'k' is a vector. Electrons have two available spins, up and down (denote spin by quantum number s=+1 and s=-1). So in the ground state, no two electrons in the system can have the same set of quantum numbers. This means each of the 10E23 electrons has a different 'k' and 's'. The ground state can be thought of as adding electrons to the system by applying the quantum 'creation operator', adding an electron of momentum 'k' and spin 's'. So the Fermi Sea is the state producted by applying the creation operator over ALL allowable k (zero to the 'k' associated w/ the Fermi energy), and over all spins. Now if you want to keep doing this integral from the vacuum state just for simple excitations of a few electrons, you are being ridiculous. Especially when you deal with non-trivial lattice potentials as well as strong electron interactions, the integrals become VERY difficult to solve. But you can always think of small excitations from the ground state in the standard electron-hole picture, which gets quite easy, especially since you can model things as Taylor expansions about the ground state where gaps can be modelled as quadratic, etc.
A thermal or other excitation above this ground state will consist of BOTH annihilating an electron with some given 'k' and 's', and then creating it with some other 'k' and 's'. Each of these operations is done with the quantum-mechanical creation and annhilation operator, which don't necessarily commute with each other (just like position and momentum operators don't commute). This leads to nontrivial quantum phenomena.
Due to the periodic lattice structure (and hence periodicity in momentum space, along with the various Brillouin Zones), there are different allowable energies for a given 'k'. So it's MUCH EASIER to model interactions from the Fermi Sea ground state as both exciting a hole and also exciting an electron, each with their associated 'k' and 's'. Such excitations can come from a variety of sources, such as magnetic interactions, lattice interactions, etc, and become very interesting and difficult to capture. Eg, it took about 50 years to get the BCS model of superconductivity at this level after discovery of superconductivity in 1911.
But anyway, this is why it's highly useful, and thus important, to consider holes. When you run through the details in this way you see holes have an effective mass, momentum, spin, etc. And they certainly can and will interact with the excited electrons as well.
Anyway, I hope this helps, and that you don't get so accusatory when people talk about holes, because physically and mathematically it makes much sense to talk about holes as excitations. Now I have to get to work, I'm spending too much time writing these things out.
make world, not war