Scientists Discover a 'Tuneable' Novel Quantum State of Matter (phys.org)

An anonymous reader quotes a report from Phys.Org: An international team of researchers led by Princeton physicist Zahid Hasan has discovered a quantum state of matter that can be "tuned" at will -- and it's 10 times more tuneable than existing theories can explain. This level of manipulability opens enormous possibilities for next-generation nanotechnologies and quantum computing. Hasan and his colleagues, whose research appears in the current issue of Nature, are calling their discovery a "novel" quantum state of matter because it is not explained by existing theories of material properties. The classical phases of matter -- solids, liquids and gases -- arise from interactions between atoms or molecules. In a quantum phase of matter, the interactions take place between electrons, and are much more complex.

[Hasan] and his colleagues arranged atoms on the surface of crystals in many different patterns and watched what happened. They used various materials prepared by collaborating groups in China, Taiwan and Princeton. One particular arrangement, a six-fold honeycomb shape called a "kagome lattice" for its resemblance to a Japanese basket-weaving pattern, led to something startling -- but only when examined under a spectromicroscope in the presence of a strong magnetic field [...]. All the known theories of physics predicted that the electrons would adhere to the six-fold underlying pattern, but instead, the electrons hovering above their atoms decided to march to their own drummer -- in a straight line, with two-fold symmetry. The decoupling between the electrons and the arrangement of atoms was surprising enough, but then the researchers applied a magnetic field and discovered that they could turn that one line in any direction they chose. Without moving the crystal lattice, [one] could rotate the line of electrons just by controlling the magnetic field around them.

Comments

"That's funny"

[FeelGood314]

The most exciting phrase to hear in science, the one that heralds new discoveries, is not “Eureka!” (I found it!) but “That’s funny ” — Isaac Asimov (OK - Asimov is credit with the quote but it's more a paraphrase of a number of quotes he made)

Sounds more classical than quantum.

[Ungrounded Lightning]

All the known theories of physics predicted that the electrons would adhere to the six-fold underlying pattern, but instead, the electrons hovering above their atoms decided to march to their own drummer -- in a straight line, with two-fold symmetry. The decoupling between the electrons and the arrangement of atoms was surprising enough, but then the researchers applied a magnetic field and discovered that they could turn that one line in any direction they chose. Without moving the crystal lattice, [one] could rotate the line of electrons just by controlling the magnetic field around them.

Sounds classical to me:
  - The layout of the substrate produced a planar potential well with no, or very little, difference of energy for electrons being in one position vs. another.
  - Provided the average density of the electrons was right, they behaved like a gas of individual particles in a thin container, or marbles on a flat surface.
  - The electrons repelled each other, so they tended to spread out evenly. (Spread out too far, though, and they leave some positive-charged substrate behind. So they don't just fly apart and go away.)
- But electrons also have spin, which means they are little magnets. So, with their mutual repulsion largely defeated by forces holding them at a given average spacing, they tend to line up north-pole-to-south-pole in strings (but don't all pile up because coming more than a little closer together under the slight magnetic attraction is balanced by higher repulsion.) The strings are a bit more dense than the average gas, so most of the electrons join one and reduce their total energy.
  - So now you have these long magnetic strings, with no preferred orientation driven by irregularities in the substrate. Bring a magnet nearby and they'll line up with its field while spacing out by mutual magnetic AND electrostatic repulsion, much like iron filing lines.

Re:Sounds more classical than quantum.

[Ungrounded Lightning]

Also: Sounds like the electrons were far enough apart and unassociated enough with the nearby nuclei that the Pauli-exclusion effects weren't constraining them into particular states - or the states were close enough together to act more like a continuum.

Re:What are the applications?

[novakyu]

And that is the correct reaction. Bose-Einstein condensate is the worst offender in overhyping their significance—name a single useful thing that came out this Nobel-prize-winning discovery!

Re:What are the applications?

[Pfhorrest]

I'm just an interested layperson, but the applications in nanotechnology seem pretty straightforward to me. Nanotech is basically all about building machines on a scale where a couple individual particles can be a whole part of the machine. So every weird thing you can figure out how to make particles do, on the individual level, at that scale -- as opposed to things to make huge aggregates of particles do -- is something you can use as a part of a nanomachine.

In this case, it sounds like they've figured out a way to build a kind of rod of electrons stuck to a crystal surface, that can be made to rotate based on the application of a magnetic field. That sounds like it could be as useful as, I dunno, a wooden disc that can be made to rotate around an axle is on a macroscopic scale. It sounds dumb and useless when you phrase it like that, but that's a rudimentary wheel, and there's a zillion uses in more complex machines that wheels can be put to. Who knows what exact uses a controllably spinning rod of electrons on the surface of a crystal could be in nanotechnology, but it seems like the kind of thing that could have many and varied.