Paper On Possible Sign Of Majorana Fermions In Solid-State System Published

I mentioned this a while back on the possible discovery of Majorna fermions in a solid state system. While the paper has appeared earlier, it has now officially been published by Science.

V. Mourik et al., Science v.336, p.1003 (2012).

Abstract: Majorana fermions are particles identical to their own antiparticles. They have been theoretically predicted to exist in topological superconductors. Here, we report electrical measurements on indium antimonide nanowires contacted with one normal (gold) and one superconducting (niobium titanium nitride) electrode. Gate voltages vary electron density and define a tunnel barrier between normal and superconducting contacts. In the presence of magnetic fields on the order of 100 millitesla, we observe bound, midgap states at zero bias voltage. These bound states remain fixed to zero bias, even when magnetic fields and gate voltages are changed over considerable ranges. Our observations support the hypothesis of Majorana fermions in nanowires coupled to superconductors. 

I'm sure they'll continue to have a better experiment to nail this down even more.

Zz.

CODATA 2010

This is the latest version (uploaded this past weekend) of the CODATA standard.

Zz.

Fundamental Constants from Topological Insulators

Already, values of fundamental constants such as "h" and "e" all came from condensed matter experiment. Now there is a proposal that another such system, a topological insulator, might yield the most precise value of the fine structure constant.

In an article appearing in Physical Review Letters, Joseph Maciejko and collaborators from Stanford University, in collaboration with SLAC, Microsoft Research, and the University of Maryland, all in the US, propose an optical experiment to measure this. The setup consists of a layer of a generic topological insulator deposited on an ordinary insulator, in a perpendicular external magnetic field. They find that measuring the rotation of light polarization reflected off the top surface (Kerr angle) and transmitted through the two layers (Faraday angle) allows one to extract the quantized magnetoelectric response. If this measurement could be realized, topological phenomena in condensed matter physics could be used to nail down the most precise values for three basic physical constants: the fundamental electric charge e, Planck’s constant h, and the speed of light c.

This should rest all arguments that condensed matter physics is merely "applied physics" and has nothing fundamental.

Note that you get free access to the paper using that link.

Zz.

The Physics of Fundamental Constants

I've always found papers that collect many of the different resources, information, and references into one coherent publication to be extremely useful. This is one such paper.

P.J. Mohr and D.B. Newell, "The physics of fundamental constants", Am. J. Phys. v.78, p.338 (2010).

Abstract: This Resource Letter provides a guide to the literature on the physics of fundamental constants and their values as determined within the International System of Units (SI). Journal articles, books, and websites that provide relevant information are surveyed. Literature on redefining the SI in terms of exact values of fundamental constants is also included.

The authors included discussions on the various major fundamental constants, how each one was determined, and a list of references! The latter is the one I appreciate the most, because it tells you how these things came about in greater detail. If you don't have the patience to follow the CODATA report, this is the next best thing.

Zz.

A Constant Constant

One of the issues that physics is trying to investigate is whether our physical constants are the same everywhere else in the universe. This just doesn't mean that it could be different in a different location of the universe due to the exotic conditions, but also at different times throughout the evolution of the universe. We have heard about the controversial idea that the fine structure constants could have varied at different times during the life of our universe.

Now comes the latest verification that comes from 6 billion light years away regarding the ratio of the mass of the proton to the mass of the electron. Murphy et al.[1] have reported that, within the limits of their experiment (which is the most accurate so far), they see no variation in this ratio. This means that this constant is the same even back that far in time.

You may read a review of this work here as well.

Zz.

[1] M.T. Murphy et al., Science v.320, p.1611 (2008).

CODATA Recommended Values of the Fundamental Physical Constants: 2006

Here are the latest CODATA set of values and measurements of the fundamental constants. I am guessing that this will appear in an issue of Rev. Mod. Phys. When that occurs, I will edit this post to include the exact citation.

Zz.

It Only Takes Two

This is a rather interesting and provocative conclusion. A group of physicists in Brazil have claimed that we only need a minimum of 2 fundamental constants to be able to arrive at all the other constants, thus, to describe our universe. {Link may be open for a limited time}

The two can be chosen, according to taste, from a list of three: the speed of light, the strength of gravity, and Planck’s constant, which relates the energy to the frequency of a particle of light, say George Matsas of the São Paulo State University and his colleagues.

Once two constants have been chosen from that list, they say, those are the only parameters that need have units of measurement ascribed to them. Everything else — for example, the charge or the mass of an electron, or the strength of nuclear forces — can be described in relation to these two 'dimensional' constants.

So far, as far as I know, this work hasn't been published yet, only appearing on the e-print arXiv. So we will have to wait until it does to see the kind of reaction and feedback it will get.

It would be interesting to compare this to an earlier manuscript titled "Trialogue on the number of fundamental constants" by M. J. Duff, L. B. Okun, G. Veneziano, where they also argue with each other on the actual number of fundamental constants that is really needed to describe our universe. It certainly would make a very interesting reading if one is getting sick of the upcoming holiday festivities!

:)

Zz.