New mechanism for superconductivity discovered in iron-based superconductors

Apr 22, 2010
Figure 1: Electronic standing waves in Fe(Se,Te) imaged by scanning tunnelling microscopy. Electronic standing waves are imaged as periodic horizontal and vertical streaks superposed on an inhomogeneous background (left column). Using a mathematical technique known as Fourier transformation, standing waves can be decomposed into components (right column). Bright spots in the Fourier maps, representing scatterings with particular characteristics, exhibit strong magnetic field dependence.

( -- A research team at RIKEN, Japan’s flagship research organisation has experimentally determined the mechanism underlying the formation of electron pairs in iron-based high-temperature superconductors. The landmark finding, reported in the April 23rd issue of Science, establishes a key role for magnetism in superconductivity.

In classical theory, occurs when two electrons are bound together to form a pair, known as a Cooper pair, by lattice vibrations. This pairing mechanism, however, has never been confirmed for high-temperature superconductors, whose transition temperatures well above the theoretical limit of about 40 K pose an enigma for condensed matter physics.

The iron-based superconductors investigated by the research team, first discovered in 2008 by Japanese researchers, offer the greatest chance of solving this enigma. With a maximum of 55K, these superconductors are governed by an electron pairing mechanism that is different from earlier mediated by lattice vibrations, one based on two types of electrons with different momenta.

New mechanism for superconductivity discovered in iron-based superconductors
Magnetic-field induced change in the intensity of electronic standing waves evidencing the “s±-wave” structure. When magnetic field is applied there appear two types of spots; one is enhanced by the field (blue) and the other is suppressed by the field (red). This behavior is evidence of the “s±-wave” structure of Cooper pairs, strongly suggesting a magnetism-related pairing mechanism.

To analyze this complex pairing mechanism, the researchers applied scanning tunnelling microscopy to electron pairing in Fe(Se, Te), the iron-based superconductor with the simplest crystal structure. Imaging electronic standing waves produced by scattering interference under a powerful 10-Tesla magnetic field, they found that Cooper pairs adopted a characteristic “s±-wave” structure that is unique to a material with two types of electrons.

The discovery of s±-wave structure breaks new ground by supporting a mechanism for electron pairing based not on lattice vibrations, as in other forms of superconductivity, but on magnetism. In providing a powerful constraint on , the finding thus marks a major advance toward unraveling the mystery of high-temperature superconductivity.

Explore further: Linking superconductivity and structure

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Apr 22, 2010
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Apr 24, 2010
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3 / 5 (2) Apr 24, 2010
This experimental discovery is extremely important. It confirms a theory that I have posted on other physics blogs, in various comments, that unifies BCS superconductivity, high temp superconductivity (cuprates) and the pnictides. The theory also extends to quantum phase transitions and superfluidity.

My theory draws from work by Arthur Winfree on coupled oscillators in the late 1960's. Kuramoto and then Steve Strogatz (Sync) developed his work further and extended Winfree's mathematical treatment. The roots go all the way back to Huygens and his pendulum clocks, around 1657.

Limit cycle oscillators have a tendency to couple. When they do, synchrony emerges. The Riken observations describe a synchrony of oscillating magnetic waves, crossing each other. Sailors know this as a seiche. The two sets of waves organize each other, through their interactions, in perfect synchrony. Forget pairing glue; think synchronized oscillations. Cooper pairs; d wave (2 x 2) synchrony; etc.
not rated yet May 01, 2010
I always find it interesting that David Radius Hudson found Superconductive Iron Based compounds and a similar issue and situations with the entire PMG (Platinum Metals Group) but no-one believed him.

Until someone else plays with it and it becomes 'fact'.

I just love it how mainstream science shoots down the very innovators that they speak of celebrating as they don't recognize the form and shape of these innovators.

It just goes to show that emotions, dogma, religion, culture, social cues, and all associated mental states permeate science as deeply as any other topic or human endeavor. The sad part is that science always goes out of it's way to exclaim some sort of immunity to human interference in it's so-called 'logic and reasoning'.

Lessons learned are that if it is mainstream and understood, it is 'average' and has nothing to do with the cutting edge. As well, stop screwing over your innovators, simply due to average scienctwits not understanding their context and metaphor.
1.5 / 5 (2) May 08, 2010
I have elaborated on my prior post (see two above) in another Phys Org article: Watching the Tug of War Between Structure and Superconductivity. My four or five posts appear approximately in the 50 to 60 range of the many posts following that article.

Briefly, structure in the BCS superconductors, in the form of phonons from the lattice, organizes BCS Cooper pairs. That is a synchrony between lattice and electrons, in which the electrons are organized into simple S wave symmetry. In the pnictides, the structure produces intersecting electromagnetic waves, which intersect at a perfect angle, producing more complex synchrony-symmetry, in an S plus minus wave. (Think invisible egg carton.) That organizes holes and other ingredients through which the current passes without friction.

The cuprates have a double interaction emerging from more complex lattice vibrations, which produces two by two or d wave synchrony. That organizes holes, etc. (repeat last sentence in prior para.)

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