from the er,-that-cleared-that-up-then... dept.
A new study by a team of physicists at Rice University, Zhejiang University, Los Alamos National Laboratory, Florida State University and the Max Planck Institute adds to the growing body of evidence supporting a theory that strange electronic behaviors -- including high-temperature superconductivity and heavy fermion physics -- arise from quantum fluctuations of strongly correlated electrons.
The study, which appeared in the Jan. 20 issue of Proceedings of the National Academy of Sciences, describes results from a series of experiments on a layered composite of cerium, rhodium and indium. The experiments tested, for the first time, a prediction from a theory about the origins of quantum criticality that was published by Rice physicist Qimiao Si and colleagues in 2001.
The ScienceDaily article may or may not be here.
(Score: 3, Interesting) by Anonymous Coward on Monday February 02 2015, @01:34AM
Give us a rough plot of what "quantum critical theory" is. I've got postgraduate degrees in EE and physics, but have no ideas what TFS is saying. How would it come across to liberal arts or even chem/bio science people?
(Score: 3, Funny) by BK on Monday February 02 2015, @02:52AM
Oh come on! Aren't we all critical of the quants?
...but you HAVE heard of me.
(Score: 2) by jimshatt on Monday February 02 2015, @11:27AM
(Score: 0) by Anonymous Coward on Monday February 02 2015, @04:57AM
As best as I can tell, it has something to do with the physics of rice and other grains.
(Score: 1) by gnuman on Monday February 02 2015, @05:05AM
http://en.wikipedia.org/wiki/Quantum_phase_transition [wikipedia.org]
http://en.wikipedia.org/wiki/Quantum_critical_point [wikipedia.org]
A quantum critical point is a special class of continuous phase transition that takes place at absolute zero, typically in a material where the phase transition temperature has been driven to zero by the application of a pressure, field or through doping.
I'm sorry, I give up! I'm not quite certain what they are talking about. I'm assuming this is not about liquid/solid/gas type conversation, but about other states, like ferromagnetism or superconductivity and the like talked in terms of phase changes of materials.
As to strongly or weakly correlated electrons, no idea. I only have an undergraduate physics degree :P
(Score: 4, Informative) by theronb on Monday February 02 2015, @05:07AM
(Score: 5, Informative) by kebes on Monday February 02 2015, @03:56PM
Short version: Some materials can order their electrons in different exotic 'phases'. This results from collective interactions between many electrons; thus the theory describing these phases is very complex. This particular paper is an attempt to gather experimental data to distinguish which theories are right/wrong.
Longer version:
Probably everyone is roughly familiar with the idea of a 'phase transition', e.g. the melting-transition of a solid turning into a liquid as heat is added. It turns out that the mathematics that describe these phase-transitions reappear throughout physics; i.e. there is something deep and universal about the concept of a discontinuous change in material properties as one crosses some threshold. (In addition to the usual phases-of-matter transitions, similar things appear in cosmology, quantum systems, magnetic systems, nuclear matter, etc.)
An interesting concept in phase-transitions is the appearance of a critical point [wikipedia.org] in the phase diagram. For instance, with the right combination of pressure and temperature, you can reach a regime where the liquid-phase and gaseous-phase become indistinguishable (e.g. at high pressure, the gas will become so dense that it will be liquid-like; but the liquid will also start becoming more gas-like, e.g. it will become compressible). There is no longer any 'boundary' between the two phases. We can this a supercritical fluid. The point at which the boundary between 'gas' and 'liquid' suddenly disappears is called the critical point. Interesting things happen near this point: materials properties are varying rapidly and can be quite different from what one would expect in either of the 'normal' phases. (E.g. water near the critical point stops being a good solvent for polar molecules!)
As mentioned before, these phase-transitions and critical-points can appear in all sorts of exotic systems. One class of systems are the strongly-correlated electron materials [wikipedia.org]. This is jargon for "the electrons in the material interact with each other a lot". If you think of the 'normal' theories of conduction (and magnetism, etc.), one can usually describe what's going on based on a single electron. In other words, you can treat each electron as being mostly independent. The total effect you see (e.g. the total current) is of course the summation of all the individual electrons, but you can predict overall behaviour just by analyzing what a single representative electron would experience. So you can assess whether a material is a conductor or insulator by looking at the band structure [wikipedia.org], etc. In "strongly correlated" systems, you can't do this. The behaviour of each electron is affecting many other electrons. They are 'strongly coupled', and so you can't ignore many-body effects [wikipedia.org] (which are notoriously difficult to resolve).
These materials thus give rise to a host of surprising and exotic phenomena ('emergent phenomena'; i.e. collective behaviour that doesn't exist at the scale of individual electrons). For instance, superconductivity [wikipedia.org] is one example. Other examples: Mott insulators [wikipedia.org] (materials that 'should be' metallic but insulate instead), complex ordering of the quantum-spins in a material (e.g. antiferromagnetism [wikipedia.org]), quantized conduction [wikipedia.org], etc. Note that these various exotic states I'm describing can be thought of as 'phases'; and so you can have a material that exhibits many of them, with 'phase-transitions' between the different behaviours. These materials are inherently interesting; they might also form the basis of interesting new technologies (e.g. spintronics [wikipedia.org], using the electron's spin, instead of its charge, as the basis for switching/computation).
Finally, the actual paper being discussed in TFA involves studying a particular exotic material (CeRhIn5) and measuring the phase diagrams it exhibits for a variety of different exotic 'quantum phases' (where each phase has a different behaviour of the electrons). Their results should have implications for a broad range of these exotic materials. In particular, they claim that their results will held distinguish which theories of quantum-criticality are supported or found to be lacking.
(Score: 2) by Gaaark on Monday February 02 2015, @06:14PM
I think they spelled it wrong:
It should be Quadrotriticale, which some people wrongly assume was inwented in Russia, but was obviously a Canadian inwention.
http://en.memory-alpha.org/wiki/Quadrotriticale/ [memory-alpha.org]
--- Please remind me if I haven't been civil to you: I'm channeling MDC. ---Gaaark 2.0 ---
(Score: 2) by KritonK on Monday February 02 2015, @08:01AM
At first glance, I thought the post was about quintotriticale [memory-alpha.org]!
(Score: 0) by Anonymous Coward on Monday February 02 2015, @01:54PM
Superconductivity has to do with energy. When electricity passes through metal that metal heats up. As the metal continues to heat if the heat is not being dissipated efficiently the metal can't just indefinitely get hotter. Instead it will simply resist further heating in the form of creating more resistance to the passage of electricity. More voltage is needed to pass more electricity in order to make it hotter. So then electrical resistance is related to temperature and naturally if you lower temperature you will reduce resistance because you are reducing the object's resistance to heat up due to electrical conductance.
(Score: 0) by Anonymous Coward on Monday February 02 2015, @02:05PM
(same poster)
If you pass a certain amount of voltage through an object what temperature will the current heat the object to before the resistance increases enough to effectively cause the current to approach zero.
(Score: 0) by Anonymous Coward on Monday February 02 2015, @02:09PM
(assuming no heat dissipation)
(Score: 2, Interesting) by fritsd on Monday February 02 2015, @04:02PM
"When electricity passes through metal that metal heats up"
Well, unless it's a Niobium-Tin alloy at 4 Kelvin [wikipedia.org], in which case it doesn't.
Then you can pump an enormous current into it and create a very strong electromagnet (see: NMR machine).
I don't know much about superconductivity but I hope the following Wikipedia article can provide a "missing link" between this Soylentnews article and the things most interested laypeople know about superconductivity:
Cooper pairs [wikipedia.org]
The "phonons" in that Wiki article are not real particles but lattice vibrations.
(Score: 0) by Anonymous Coward on Monday February 02 2015, @05:49PM
(Original poster) Thanks. Yeah I don't really know that much about it either but I found this interesting.
http://en.wikipedia.org/wiki/Superconductivity [wikipedia.org]