Tag Archives: Superconductivity

Evidences of Majorana Particles Seen In Nanowires

A particle can be its own anti-particle – this was the phenomenal insight of the mysterious physics genius Ettiore Majorana, who went missing in 1938 and was never found. These particles have been widely searched for and has generated considerable amount of interest in the theoretical physics community, but have not been found. Now, the LHC has been quite actively searching for signatures of these particles.

A computer image of the nanowire created

Condensed Matter physicists join in…

Interestingly, and very importantly, a lot of modern day condensed matter research focusses on the type of signatures that Majorana particles can produce and how they can be detected. It is in this context that wonderful news comes in from a team of Dutch researchers, who have reported seeing signatures for these particles.

Device and Methodology

The team has been fabricated a device which comprises a nanowire forming a junction between a semiconductor and a superconductor. The team then applied a magnetic field parallel to the nanowire and this restricts electrons to only certain energies, creating so-called ‘band gaps’. Electrons can reside only in these band gaps.

The team then measured the conductivity of the material given different gate voltages and found that there are two small peaks in the conductances placed symmetrically about the zero bias voltage. Scientists think that these peaks are due to particles and anti-particles respectively, but they are just the same, i.e. they are Majorana fermions.

The team varied the magnetic field and the bias voltage over large ranges of values, but they dips stayed constant. All of this leads the team to conclude that the charge carriers in nanowire were indeed Majorana fermions.

The work appears here: http://www.sciencemag.org/content/early/2012/04/11/science.1222360.full.pdf

Novel Superconducting Material Does The Impossible; May Open Up New Possibilities in Solid State Physics

Whether this has the same effect as Silicon had in revolutionising solid state devices is something that only time will tell, but this certainly seems to have a lot of potential. Researchers at the Stanford Institute for Materials and Energy Sciences (SIMES) have been able to synthesize a new material by sandwiching two nonmagnetic insulators together. The wonderful property is that within this substance, both superconductivity and magnetism exist simultaneously.

A Magical Property

Meissner Effect

Superconductors are substances which allow the flow of current almost unhindered, unlike ordinary conductors, which have resistance. The flow is almost 100% efficient. A peculiar property unique to superconductors is that they expel any magnetic field within them by the so-called Meissner Effect. Ordinary spherical conductors allow a uniform non-zero magnetic field within them. One of the signatures of the onset of superconductivity when such a conductor is cooled is the almost sudden drop of this internal field to zero. So, superconductivity and magnetic field are uncomfortable bedfellows.

New Magical Material

In this novel substance, made by strapping together a thin film of lanthanum aluminate on a strontium titanate substrate, both superconductivity and magnetic field exist together at the boundary. At this junction, current flows with no resistance.

Never has it been seen that superconductivity and magnetic fields help each other. The researchers are still to establish the relation in this system. If they assist one another, it will again pose another interesting problem to the already bulging bag of puzzles in superconductivity. Scientists at MIT confirmed that superconductivity and magnetism indeed exist at the boundary.

Looking for more

The SIMES group is looking at the response of the substance to externally applied electric fields, especially alternating ones. They are also looking at how the substance reacts to being compressed. No one knows why superconductivity and magnetism coexist and that too at the boundary of two nonmagnetic non-metallic substances, but they suspect that some new phenomenon might be afoot contributing to both these effects.

There is, indeed, more magic in physical phenomena than in heaven and earth.

Addictive Physics: Superconductivity Can Be Induced By Red Wine

Here’s another excuse you might find handy (or, maybe, not) for buying that bottle of red wine you always wanted: to do physics. Yes, that’s right, physics. Apparently, red wine can lead to better superconducting properties in certain alloys. This find was reported by a team of researchers based in Japan.

Superconductivity is a phenomenon exhibited by certain substances (pure metals or synthesized alloys) that display zero resistance to the flow of electric current. For example, if you cool mercury to 4.2 Kelvin (which is about minus 269 Celsius), it shows an abrupt decrease of electrical resistance. The resistance, in fact, suddenly goes to a value very close to zero.

Superconductivity sets at a critical temperature, Tc, at which the resistivity goes down to zero.

If a current is induced in the superconductor, it will be maintained without any supporting voltage for a very long, practically infinite, time. In case of normal conductors, like copper at room temperature, the current dies out, because of loss of energy by heating due to the resistance of the material. Interestingly, this property can be used to levitate magnets by exploting the so-called Meissner Effect. Watch the amazing video.

The focus of material sciences in recent times has been to find substances which show superconducting properties at higher temperatures. Such materials are called High Temperature Superconductors’ (HTc Superconductors). If a material is found such that it is superconducting at room temperatures, it will lead to huge leaps in electrical transport efficiency.  A few such materials are known, giving superconductivity at 30 K or -243 0C (LaBaCuO, for the science buffs) or at 92 K (YBaCuO). (The black slab in the above video is YBaCuO cooled by liquid nitrogen.)

Generally, bulk superconductivity is shown in materials after being treated appropriately. In a substance called Iron-Tellurium Sulphide (FeTe1-xSx), bulk superconductivity can be induced at quite high temperatures by immersion in water-ethanol mixture and oxygen annealing. (If the formulas bother you too much, just ignore them. These are not integral to the story.) The Japanese research team has discovered that superconductivity can be induced by heating the material in red-wine at 70 0C for 24 hours, after which it becomes superconducting at 9.9 K. More importantly, the quality of superconductor produced is high. (For science buffs, the shielding volume fraction, which is a measure of how good the superconductor is, is highest for FeTe0.8S0.2 boiled with red wine.)

The reason for this induction of superconductivity is not known.

The next time you see that expensive bottle of red wine, think superconductors’.  Here’s another bottle of champagne, err, wine in celebration of this discovery.