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Has the Mythical Unicorn of Materials Science Finally Been Found? 238

gbrumfiel writes "For years, physicists have been on the hunt for a material so weird, it might as well be what unicorn horns are made of. Topological insulators are special types of material that conduct electricity, but only on their outermost surface. If they exist, and that's a real IF, then they would play host to all sorts of bizarre phenomenon: virtual particles that are their own anti-particles, strange quantum effects, dogs and cats living together, that sort of thing. Now three independent teams think they've finally found the stuff that the dreams of theoretical physicists are made of: samarium hexaboride."
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Has the Mythical Unicorn of Materials Science Finally Been Found?

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  • Re:Boring (Score:5, Informative)

    by Anon-Admin ( 443764 ) on Wednesday December 12, 2012 @12:23PM (#42261475) Journal

    How about Trilithium Nitrate?

    http://www.chemspider.com/Chemical-Structure.19054984.html [chemspider.com]


    Trilithium borate

    http://www.chemspider.com/Chemical-Structure.13208905.html [chemspider.com]

    I am not sure that three lithium atoms will bond on there own with out something else in the structure. ;P

  • by Anonymous Coward on Wednesday December 12, 2012 @12:48PM (#42261825)

    The summary includes the caveat: "If they exist, and that's a real IF".

    This is baffling, as the first topological insulators were experimentally confirmed several years ago(the family Bi2Se3, Bi2Te3, Sb2Te3, Zhang, et al. Nat Phys 5, 438 (2009)). While samarium hexaboride has some unique wrinkles in terms of physics at play, the major reason for interest is chemical. The materials above are prone the oxidation and vacancies, which shifts the fermi energy into the bulk. This means that the bulk is not fully insulating, even though the topological insulator hallmarks are still readily observable using the right experimental techniques. Samarium hexaboride appears to have a much more strongly insulating bulk, making it in some sense a much "cleaner" example.

  • IEEE July 2011 (Score:5, Informative)

    by Anonymous Coward on Wednesday December 12, 2012 @12:51PM (#42261893)

    This is a better description of Topological Insulators [ieee.org] from IEEE in July 2011. Not real sure what can be done with these things in practice. They have interesting properties, though.

  • by AvitarX ( 172628 ) <`gro.derdnuheniwydnarb' `ta' `em'> on Wednesday December 12, 2012 @12:58PM (#42262035) Journal

    A Deist, non-acting God is indistinguishable from physics (thus your calling it philosophy).

    But one is visible/observable (physics/universe) the other is not.

    Creating IPU or FSM is no different than creating God, unless you demonstrate the universe didn't always exist.

    Fact, we have universe and physics

    It may not have always existed

    Now you're inventing something untestable to fill what may or may not be the case. And the something (capital G God) is attributed to a hell of a lot more than just creating the universe, much of which is falsifiable.

    Why can God be attributed universe creation, but not IPU?

  • by Anonymous Coward on Wednesday December 12, 2012 @01:26PM (#42262475)

    There is actually a good reason for using "insulator" instead of "conductor". The conducting surface is a just consequence of the kind of insulating phase in the bulk rather than the central feature; it really is an kind of insulator that has conducting surface state.

    Until pretty recently most phase transitions could be traced to a breaking of symmetry, and described using something called an order parameter. Superconductivity, for example, is a consequence of breaking gauge symmetry. Topological phases, on the other hand, do *not* have an associated order parameter. They are, as you might guess from the name, distinct from trivial phases in a discrete way(and as such are robust under perturbation), and can be classified by an integer parameter.

    Topological insulators are an insulating phase that is distinct from normal insulating phases in that you cannot change to one from the other without changing it to a metal first. In a very (very) vague sense, in a topological insulator these electronic states are twisted around one another such that in order to unwind them you have to break them by making it a metal first.

    This is why the surface states are metallic. At the surface you are going from the topological phase to the trivial phase, and in order for the electronic states to unwind they have to become metallic at some point. You cannot get rid of the metallic states without destroying the topological insulating bulk phase. Furthermore, this metallic surface state will be a Dirac cone, like in graphene. So these aren't just any metallic states, they are very special ones.

    In any event, the summary is wrong. This is not the first topological insulator experimentally verified. It's just a particularly clean example, and has additional interesting wrinkles making it worth study.

    Also, if you don't like the name, it's way, way too late to hope for a change. It's been around for five years, and many thousands of papers have been written about it. Phys Rev has an RSS feed for papers on just this topic.

  • by S77IM ( 1371931 ) on Wednesday December 12, 2012 @03:34PM (#42264089)

    For those of you playing along at home, what you're seeing is an example of the Cosmological Argument [wikipedia.org] for the existence of God. It's one of my favorites, because there's no way to prove it correct or incorrect, so you can keep arguing forever!

      -- 77IM

  • Re:are there any (Score:5, Informative)

    by slew ( 2918 ) on Wednesday December 12, 2012 @08:26PM (#42267433)

    This post is clearly extremely informative despite the fact that I did not understand any of it. But to the OP's question, though, what would some practical applications actually be?

    Well, let's see if I can be a bit more specific for the typical /. user. Although there are other uses for spintronics, the current "killer" app for spintronics is high density non-volatile storage.

    The most popular user application for spintronics has been the Giant MagnetoResistive (aka GMR) read-heads used in modern disc drives to allow them to have much higher bit-density than previous generation technology. A less popular uses that may not be as familiar to the typcial /. user is the MRAM (or magneto-resistive RAM), or some magneto-resistive sensors (used in solid state compasses inside devices like cellphones and GPS car navigators).

    The underlying physics of the GMR technology is complicated, but is the result of the QM effects related to the thin layers of alternating feromagnetic materials in the read-head resulting in certain spin-statistics of the electrons in those layers. Without getting into details, the net result is that a small magnetic field can cause a giant change in resistance which can be measured (hence the name GMR) allowing much smaller magnetic domains to be used resulting in increased storage density. This is a basic application of spintronics.

    For this specific advance, it probably wouldn't be directly applicable to GMR heads, but possibly advanced spintronic based storage beyond MRAMs and racetrack memory [wikipedia.org]. Having chip interconnect that can reliably transport electron spin information will allow for much more efficient devices.

    The reason that people are looking at spintronics based storage is that in addition to the density and the non-volatile nature, the access time and durability is potentially much better than flash memory [slashdot.org]. Doing things to approach the theoretical density would be a great advance.

    Does that help?

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