Seeing Superconductivity

September 4, 2009 | 3 Comments

Researchers at the Brookhaven National Laboratory at Cornell University and the Institute of Advanced Industrial Science and Technology, Japan, in a paper published in Science August 28th, 2009 show for the first time that the spectroscopic “fingerprint” of high-temperature superconductivity remains intact well above the super cold temperatures at which these materials carry current with no resistance. This confirms that certain conditions necessary for superconductivity exist at the warmer temperatures that would make these materials practical for energy-saving applications — if scientists can figure out how to get the current flowing.

Physicist J.C. Seamus Davis at Brookhaven explains, “Our measurements give the most definitive spectroscopic evidence that the material we studied is a superconductor, even above the transition temperature, but one without the quantum phase coherence required for current to flow with no resistance.  The spectroscopic ‘fingerprint’ confirms that, at these higher temperatures, electrons are pairing up as they must in a superconductor, but for some reason they are not co-operating coherently to carry current.”

Brookhaven's Quasiparticle Interference Image

Brookhaven's Quasiparticle Interference Image

The spectroscopic “fingerprint” might show what inhibits coherent superconductivity at higher temperatures. That knowledge might then help scientists achieve the ultimate goal of developing super-conducting materials for real-world practical devices such as zero-loss power transmission lines.  If they can get to temperatures warm enough, many things not even in consideration today would be possible greatly reducing the current needed for electrical powered work.

Many previous studies have hinted that the higher temperature “parent” state in copper-oxide, or cuprate, superconductors might be a “quantum phase incoherent” superconductor, a state in which electron pairs exist but don’t flow coherently as they do below the transition to superconducting temperature.  Davis says, “But the methods used in these studies were indirect. Each of the results could be described by alternate explanations. What we were searching for was an incontrovertible signature.”

Using a spectroscopic imaging scanning tunneling microscopy method developed over many years, Davis and his collaborators had previously conducted extensive studies of the superconducting state of a copper-oxide superconductor containing bismuth, strontium, and calcium (known as BSCCO). These studies identified a detailed spectroscopic signature containing all the quantum mechanical details of that superconducting state.

The team then set out in a new study designed to see whether the signature changed when the material was warmed above the transition temperature, which is 37 kelvin, or –236º C and -392.79º F. This was a major challenge because the method works best at very cold temperatures. As materials warm up, electrons start moving around more energetically, decreasing the resolution of the measurements.

Davis says, “We had to make a series of modifications to greatly increase the signal-to-noise ratio for all measurements.”  Some measurements were made over a period of up to 10 days. By averaging measurements over those long times, the scientists were better able to isolate a weak signal from the random background noise.

The results were definitive: “We found that the characteristic signature passes unchanged from the superconducting state into the parent state — up to temperatures of at least 55 K — or 1.5 times the transition temperature,” Davis said. “We know of no explanation for why this fingerprint should remain other than that it represents the phase-incoherent superconducting state which has been proposed to exist based on other kinds of measurements.”

Which leads to the inevitable if newly discovered questions, ‘Why could the parent state condition be indeed an “incoherent” superconductor.’ Davis asks, “What breaks the cooperation of the electron pairs? What is the problem that is overwhelming the superconductivity?”  That’s the issue. The fingerprint shows the parent temperature could, but doesn’t perform.

Davis’s technique can address such question in a quantitative manner. For example, by varying the chemical composition, level of doping, or characteristics of the copper-oxide planes in the layered material, the scientists can measure the strength of quantum phase fluctuations affecting the electron-pair cohesion.  That might be an ‘Ah Ha’ moment in the years to come.

Davis’ method of measurement may help scientists zero in on ways to induce coherent superconductivity at a higher range of temperatures than previously thought possible. And that would be an essential step to achieving real-world applications without the need for expensive cooling systems.

The implications are truly mind-boggling.  Should superconducting magnets become available in the ranges needed for atom confinement, some fusion projects might work, others that might otherwise work could be much cheaper to build and operate.  Motors would be more powerful.  If the technology develops to the integrated circuit, computer speeds would soar.  It’s just an incredible list; just get superconductivity to 100º C or 212º F and the possibilities are staggering.

One more point – The Brookhaven press release is one of the best ones I’ve seen. Thanks to the writer too!  Pass it on.


3 Comments so far

  1. single parent adoptions on September 21, 2009 1:28 PM

    Thought provoking post. Very interesting and enjoyed it a lot.

  2. Retherford on May 10, 2010 10:08 PM

    Thanks for this, Ive always wondered. Great job explaining it for me!

  3. Tam on May 10, 2010 11:07 PM

    Thanks for this, I’ve always wondered. Great job explaining it for me!

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