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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.
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."
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.
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.
"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
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 are not a science or engineering student, you probably don't care).
Satyendranath (sp?) Bose came up with the bombshell that although Bolztman's law is right Bolztman's law operates differently for quantum particles. Some quantum particles (nowadays called Bosons) are more likely than expected to get into the same quantum state. They will do this wheneve the temperature is low enough
that their momentum uncertainty forces their position uncertainty to be at least as large as the typical distance between partciles (i.e their wavefunctions must "overlap" coherently, and again if you don't understand, you don't care).
So even ordinary BECs happen at relatively high temeratures. Unfortunately these temperatures are still in the nanokelvin range, at least for atoms under experimental conditions.
Carter: "Well how do *you* think it's done".
Oneil: "Magnets."
Yes, but only if you route the plasma conduits through the Heisenberg compensators.
-- Alastair
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.
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 which lots of quantum particles sit around and interact strongly, and of those, it is probably the most experimentally accessible. As for BEC in solid state quasiparticles, time will tell and I can only speculate from a position of ignorance. On the one hand it might sacrifice what I called "expermantal accessiblilty", because you have to deal with all the muck inside real solids, on the other hand a high temperature condensate made of magnons seems a lot more practical than normal condensates. Maybe it is easy to interface it to electronic control and measurement, so you can create and probe all kinds of weird and wonderful quantum states. Don't be surised if someone comes up with a paper trying to plug this as the next big thing in Quantum Computation.
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.
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