Topological Superconductor?

We know how "hot" topological insulator is right now in condensed matter. Huge amount of publications are pouring out on this family of material. Well, it seems that in one type of topological insulator, B12Se3, when doped with copper, it becomes what is claimed to be a topological superconductor! This is where the material becomes a superconductor in the bulk of the material, but still becomes a normal metal on the surface.

Generally, metals, insulators and conventional superconductors tend to have a single type of behavior as far as electricity goes. They can either conduct current or not, and remain consistent in they way they respond to electrical charges.

“The known states of electronic matter are insulators, metals, magnets, semiconductors and superconductors, and each of them has brought us new technology,” explains M. Zahid Hasan.

“Topological superconductors are superconducting everywhere but on the surface, where they are metallic; this leads to many possibilities for applications,” adds the expert.

Here is the abstract from the Nature Physics paper[1]:

Experimental observation of topological order in three-dimensional bulk solids has recently led to a flurry of research activity. Unlike the two-dimensional electron gas or quantum Hall systems, three-dimensional topological insulators can harbour superconductivity and magnetism, making it possible to study the interplay between topologically ordered phases and broken-symmetry states. One outcome of this interplay is the possible realization of Majorana fermions—quasiparticles that are their own antiparticles—on topological surfaces, which is of great interest in fundamental physics. Here we present measurements of the bulk and surface electron dynamics in Bi2Se3 doped with copper with a transition temperature Tc up to 3.8 K, observing its topological character for the first time. Our data show that superconductivity occurs in a bulk relativistic quasiparticle regime where an unusual doping mechanism causes the spin-polarized topological surface states to remain well preserved at the Fermi level of the superconductor where Cooper pairing takes place. These results suggest that the electron dynamics in superconducting Bi2Se3 are suitable for trapping non-Abelian Majorana fermions. Details of our observations constitute important clues for developing a general theory of topological superconductivity in doped topological insulators.

Zz.

[1] L.A. Wray et al., Nature Physics v.6, p.855 (2010).

Much Ado About Topological Insulators

Topological Insulators are HOT. They are the hottest thing in condensed matter physics right now. This news summary from Nature describes what they are, and why they are the 'star' material at this moment (link open only for a limited time).

Those effects go beyond the way electrons move on the surface. For example, all electrons are spinning in a quantum mechanical way. Usually, the spins are constantly knocked about by random collisions and stray magnetic fields. But spinning electrons on the surface of a topological insulator are protected from disruption by quantum effects. This could make the materials beneficial for spin-related electronics, which would use the orientation of the electron spin to encode information, thereby opening up a whole new realm of computer technology.
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Researchers also believe that the collective motions of electrons inside topological insulators will mimic several of the never-before-seen particles predicted by high-energy physicists. Among them are axions, hypothetical particles predicted in the 1970s; magnetic monopoles, single points of north and south magnetism; and Majorana particles — massless, chargeless entities that can serve as their own antiparticles.

This mimicry is not entirely surprising. Almost by definition, collective electron motions can be described by just a handful of variables obeying simple equations, says Frank Wilczek, a Nobel-prizewinning particle physicist at the Massachusetts Institute of Technology in Cambridge. "There are only a few kinds of equations that you can write down that are really simple," he says. So topological-insulator theorists and particle physicists have almost inevitably ended up in the same place.

In other words, once again, the physics that governs things in condensed matter now have implications into other areas that may be fundamental in nature! How many times have I indicated this already?

And since we're talking about topological insulators, don't miss the latest STM study on something similar that has produced quite an interesting result.

Zz.

The Science of Tangled Cord

Next time you have to untangled the cords from your electronics, you can at least think of it as a complicated physics process. :)

This news article describes a recent PNAS paper on this very issue.

Knot formation had been studied a lot by mathematicians, but not much by physicists. Smith was worried that the work wouldn't be taken seriously, but it ended up being published in the prestigious Proceedings of the National Academy of Sciences.

"The way that you get a knot is the string has to bend back on itself, coil back on itself," Smith said. As a string or cord tumbles, the end of it has a 50 percent chance of weaving to the left or the right of the coils, and under or over the coils, sort of like random braiding, Smith said.

The exact citation for this paper (which none of these popular newspapers ever give) is:

Dorian M. Raymer and Douglas E. Smith, PNAS v.104, p.16432 (2007).

Don't get all tied up with it.

:)

Zz.