Prediction of superconductivity in compounds based on iridium oxide opens a new chapter for superconductors

May 31, 2013
Figure 1: The layer-like crystal structure of the iridium oxide Sr2IrO4. Strontium, iridium and oxygen atoms are shown in blue, red and white, respectively. Credit: 2013 Seiji Yunoki, RIKEN Center for Emergent Matter Science

High-temperature superconductors are some of the most widely studied materials in physics, where the discovery of new compounds often provides insight into the complex physics that underlies them, as well as revealing interesting new electronic phenomena. Seiji Yunoki and colleagues from the Computational Quantum Matter Research Team at the RIKEN Center for Emergent Matter Science may have made such a discovery through their prediction of an unconventional superconducting phase in compounds based on iridium oxide.

The high-temperature superconductors commonly investigated by scientists are often structures consisting of different stacked on top of each other. It is along these atomic planes that the superconducting electrical currents flow. Interestingly, the iridium oxide Sr2IrO4 studied by Yunoki and his colleagues has a very similar layered structure (Fig. 1). The magnetic arrangement of the atoms in these layers—important for the superconducting state in such materials—is also similar to that in copper oxides.

Not everything in the iridium oxide system is comparable to that in copper oxides, however. Iridium is a far heavier element than copper, and its outer electrons circle the atomic cores at a much greater distance. The different path of these electrons also influences their , or spin. Indeed, 'spin-orbit coupling' leads to very different spin effects in the iridium oxides that influence not only superconductivity, but also other electronic properties—including those that make iridium oxides of possible interest for .

"A number of groups have tried to make iridium oxide superconductors," says Yunoki. "So far, they have been able to make the compound metallic, but they have not yet succeeded in making it superconducting."

To probe the possible reasons for the elusiveness of superconductivity in iridium oxides, Yunoki's team developed a theoretical model to describe the compound's properties. They were able to calculate that superconductivity could be achieved by introducing atoms of other elements to provide a surplus of electrons—a process known as electron doping. "This is exactly where our theoretical work becomes valuable," says Yunoki. "We have provided a guideline by showing that, as opposed to copper oxides, the superconductivity in Sr2IrO4 appears most likely with an electron surplus, not with a deficit."

The researchers now plan to assist in the search for iridium oxide superconductors, and to investigate possible applications of their compound's spin properties in electronics. Already one of the rarest elements in the Earth's crust, Iridium's true value may therefore be hiding in its useful electronic properties.

Explore further: New ways to tune electrical conductivity revealed by electron interaction

More information: Watanabe, H., Shirakawa, T. & Yunoki, S. Monte Carlo study of an unconventional superconducting phase in iridium oxide Jeff = 1/2 Mott insulators induced by carrier doping. Physical Review Letters 110, 027002 (2013).

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1 / 5 (4) Jun 01, 2013
They were able to calculate that superconductivity could be achieved by introducing atoms of other elements to provide a surplus of electrons—a process known as electron doping.

Talking of reinventing the wheel: This has been known for more than 8 years by now! See the discussion of YBCO in
2 / 5 (4) Jun 01, 2013
Yep, but you "forget" to mention iridium during it...;-) Anyway, from perspective of practical applications, the iridium is the least usable element for superconductors due to its terrific price. IMO the Sr2IrO4 will not work as a superconductor anyway, because the Ir(IV) oxidation state is more stable, than Cu(III) in cuprates and the superconductivity requires the excessive electrons to work. After all, we have room superconductors developed from cheap components already - they're just overlooked with mainstream physics in similar way, like the cold fusion and/or magnetic motor technologies.
1 / 5 (1) Jul 08, 2013
The only reason for not finding a room temperature superconductor is because the atom is slightly misunderstood. The model needs an adjustment in the power of the orbitals. Each one condenses a previous and the stages of development through the various elements is happening everywhere all the time, the earth is growing despite the measurements disproving it, there are other explanations to cover. First the composition of our universe is based upon the photon. When photons combine an electron can be the result. Many photons become electrons flying out from the sun, which may combine with other electrons if the angle and velocities are right a "proton" can be born. Double this "proton" and invert the charge, and it becomes a neutron., this is a more accurate picture of "how" and atom is built up. Each stage "encapsulating" the previous, creating pressures inward. Electrons are all around us in many forms, on the fringes of atoms, "sewing" them together.
1 / 5 (1) Jul 08, 2013
part 2::
Protons are inverted charge electrons and so attract. Having an "oxide" on the surface promotes extra electrons while a compressed "proton" core such as barium bombarded and compressed by "freeze forming nanoparticles" then adding an oxide exterior would most likely result in such a material... compress a more electro positive material, bring it into less space and then coat with an oxidizer of a heavy metal..

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