Monday, October 13, 2008

Superconductivity Advance

This is a bit of very intriguing news from the laboratory. Of course we have been touting the promise of superconductors for decades and progress has been at a snail’s pace due to the very real problem of low temperatures.

In the end we want room temperature superconductors that we can sandwich between two thin films. We obviously have a long ways to go but this work shows that we are not kidding ourselves.

You may want to ask why we care. It turns out that a magnetic field will not penetrate a superconducting material. Therefore it seems reasonable that a craft clad with a superconducting skin will exclude the Earth’s magnetic field and in the process provide lift.

The craft would likely still need to be light weight and also pack a lot of power, but would behave a little like a balloon while flying since it will be very buoyant.

If we are lucky, we may be able to use such technology to lift material into space. Once there it will be possible to map magnetic fields and perhaps take advantage of them to assist transporting goods long distances through space.

We will still need a continuous one G trust in order to move manpower and mass any distance and in order to actually explore the solar system in a reasonable time frame.

By the way this is one more brick in my hypothesis that humanity has already done this around fifteen thousand years ago. Our understanding of the enabling technology behind UFO’s is now becoming much clearer. We now know were it is leading.

New form of superconduction observed in interfaces

By Todd Morton Published: October 08, 2008 - 12:01PM CT

Ars has brought you lots of coverage of
research in superconductivity, including the discovery of a new class of superconductors and a new theory that attempts to describe the phenomenon. As it's a branch of physics that is poorly understood, research efforts often lead to new observations of the phenomenon and new questions, rather than solutions to existing questions. A paper to be published in Nature today falls squarely into the new-observations category. Researchers have observed superconductivity at the interface of two materials that are not inherently superconducting at any temperature, suggesting that we can engineer superconductors at small dimensions.

The generally accepted explanation for superconduction involves Cooper Pairs, where two electrons become weakly coupled at a relatively large distance (several nanometers) through an interaction with phonons (heat's quantum equivalent to the photon) that are vibrating in the crystal lattice. If one electron is impeded by a normal scattering site like an impurity or crystal imperfection, the other electron in the pair can "pull" it along.

The interaction is so weak that temperatures above 30K will break the pair, so this model works to describe pure metals that superconduct at temperatures below 10K. The theory breaks down for high-temperature oxide superconductors, which have achieved superconduction at temperatures as high as 138K (at atmospheric pressure). Clearly there are other mechanisms at work, but we don’t currently understand them.

The new research involved a lanthanum copper oxide compound that can be doped over a wide range of compositions, which was used to study a potentially new mechanism of superconduction. A substrate of LaSrCuO4 was used, and an epitaxy technique grew atomically-perfect thin films of three derivative compounds: an insulator and a metal that show no superconductivity, and a superconducting variant with a transition temperature (Tc) of 40K. By growing literally hundreds of combination of interfaces and film thicknesses, the researchers were able to observe superconduction at different temperatures, including superconduction at the metal/insulator interface.

The authors took great lengths to characterize the materials and confirmed that the interface was both atomically perfect and pure, meaning that a third material was not formed from inter-layer mixing. This means that an interface interaction is responsible for the superconduction. By varying the thickness of the films used, the authors found that the superconductivity was occurring in just two unit cells around the interface. Interfaces produced with a superconducting variant boosted its Tc from 40K to 50K, while interfaces with the two nonsuperconducting layers had Tc's as high as 30K.

While there is no definitive explanation available for this interfacial superconduction, it opens the door for further research into engineering superconductors out of non-superconducting materials. The small length scales at which the superconduction occurs may make it appropriate for micro- and nanoscale devices.

Nature, 2008. DOI:
10.1038/nature07293

Letter

Nature 455, 782-785 (9 October 2008) doi:10.1038/nature07293; Received 15 June 2007; Accepted 25 July 2008

High-temperature interface superconductivity between metallic and insulating copper oxides

A. Gozar
1, G. Logvenov1, L. Fitting Kourkoutis2, A. T. Bollinger1, L. A. Giannuzzi3, D. A. Muller2 & I. Bozovic1
1. Brookhaven National Laboratory, Upton, New York 11973-5000, USA
2. School of Applied and Engineering Physics, Cornell University, Ithaca, New York 14853, USA
3. FEI Company, Hillsboro, Oregon 97124, USA

Correspondence to: I. Bozovic
1 Correspondence and requests for materials should be addressed to I.B. (Email: bozovic@bnl.gov).

The realization of high-transition-temperature (high-T c) superconductivity confined to nanometre-sized interfaces has been a long-standing goal because of potential applications
1, 2 and the opportunity to study quantum phenomena in reduced dimensions3, 4. This has been, however, a challenging target: in conventional metals, the high electron density restricts interface effects (such as carrier depletion or accumulation) to a region much narrower than the coherence length, which is the scale necessary for superconductivity to occur. By contrast, in copper oxides the carrier density is low whereas T c is high and the coherence length very short, which provides an opportunity—but at a price: the interface must be atomically perfect. Here we report superconductivity in bilayers consisting of an insulator (La2CuO4) and a metal (La1.55Sr0.45CuO4), neither of which is superconducting in isolation. In these bilayers, T c is either 15 K or 30 K, depending on the layering sequence. This highly robust phenomenon is confined within 2–3 nm of the interface. If such a bilayer is exposed to ozone, T c exceeds 50 K, and this enhanced superconductivity is also shown to originate from an interface layer about 1–2 unit cells thick. Enhancement of T c in bilayer systems was observed previously5 but the essential role of the interface was not recognized at the time.

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