Superconductor Puzzle

There has been a numberofadvances in the field of superconductingrecently. Superconductors, materials that conduct electricitywith noresistance below a certain temperature (the criticaltemperature,T_c), have a variety of incredibleapplications. For example, superconductors could offerelectricity transmissionwith no losses from power plants, savingthe country's money andfuel, could power faster computers, andcould make ultra-efficientmotors.

Over the last few years, many breakthroughs in the fieldofconductivity have been achieved.  The firstsuperinsulatorshave been created and magnetism-immunesuperconductors have alsobeen made.  The greatest goal ofsuperconductor research -- toachieve room temperaturesuperconductivity -- still remainsunattained, but thanks to newcuprate (copper and oxygen)superconductors we're a lot closer.

However, one critical problem was that superconductor behaviorinthese cuprate superconductors were not well understood --untilnow.  Researchers at U.S. Department of Energy'sBrookhavenNational Laboratory along with partners from CornellUniversity,Tokyo University, the University of California,Berkeley, and theUniversity of Colorado have finally developed acohesiveexplanation for superconductor behavior.

To gain their insight, the researchers used"quasiparticleinterference imaging" with a scanning tunnelingmicroscope to lookat Cooper pairs of electrons.  Cooper pairsare pairedelectrons in superconductors that allow for the phenomenatooccur.

The puzzling phenomena, which the scientists solved, was thatinnormal superconductors raising the binding energy, to holdthesepairs together raises the critical temperature closer toroomtemperature.  However, in cuprate superconductors, whichhavehigher starting temperatures, raising the binding energyactuallylowers the T_c, the opposite of the desiredresult.

Researchers determined that this is due to a "quantum trafficjam"effect.  Normally cuprates are stuck in a jammed statedknownas the Mott insulating state, named after the late Sir NevilleMottof Cambridge, UK.  To create cupratesuperconductors,electrons are removed from cuprates, leavingholes.  Cooperpairs can then start to flow into these holes,allowing forsuperconduction, akin to a couple cars exiting thehighway duringrush hour starting traffic moving.

However, the critical discovery the researchers made wasthatincreasing the binding energy also increased the "Mottness"ofcuprate superconductors.  Thus, raising the temperatureonlymade the traffic jam worse, lowering thecriticaltemperature.  Seamus Davis of Brookhaven NationalLaboratoryand Cornell University, lead author on the paperdescribes, "It hasbeen a frustrating and embarrassing problem toexplain why this isthe case."

Now the dilemma becomes applying this new knowledge tonewsuperconductors.  Traditional superconductors havelowMottness, allowing for binding energies to be used to raisetheircritical temperature.  However, they start at verylowcritical temperatures, so the temperature can only be raisedsohigh, typically well below the starting critical temperaturesofcuprate superconductors.  Cuprate superconductors starthigh,but can't get any lower.

A new hope is that superconductors comprised of arsenic andiron,instead of copper and oxygen, might have less Mottness, but beableto make gains from raising binding energies, but also enjoyhigherstarting temperatures.  Mr. Davis states, "We need tolook formaterials with such strong pairing but which don't exhibitthisMottness or 'quantum traffic-jam' effect.  Our hope isthat(iron/arsenic superconductors) will have less 'traffic-jam'effectwhile having stronger electron pairing."

If such a superconductor can be created and tuned, roomtemperaturesuperconductivity may finally be achieved, andaffordable, bringinggreat economic and scientific gains.  Fornow, thebreakthrough represents perhaps the greatest advanceinunderstanding superconductivity yet.

 Posted by DailyTech

A pellet of yttrium bariumcuprate,when exposed to a styrofoam cup filled with liquidnitrogen,superconducts and levitates a neodymium magnet. Scientistshavefinally figured out how these superconductors and others work,amystery that has long eluded them.  (Source: coronene.com)