At the end of the day, we want athin superconducting layer to produce the skin of a magnetic field exclusionvessel (MFEV), also known as an UFO. Weare here one step closer.
It has been gratifying to seesteady progress in these necessary areas since I published my piece on thereverse engineering of an UFO. It isgoing very well and we should be able to mock up a device inside of the decade.
This was one of the key technologies:manufacture of a single superconducting layer of high temperaturesuperconductor. A single layer coolingsubstrate would also be good.
Exploring the Superconducting Transition in Ultra Thin Films
by Staff WritersUpton NY
Ivan Bozovic.
Like atomic-level bricklayers, researchers from the
The technical break-through, which is described in the April 28,2011, issue of Nature, is already leading to advances in understandinghigh-temperature superconductivity, and could also accelerate the developmentof resistance-free electronic devices.
"Understanding exactly what happens when a normally insulatingcopper-oxide material transitions from the insulating to the superconductingstate is one of the great mysteries of modern physics," said Brookhaven physicistIvan Bozovic, lead author on the study.
One way to explore the transition is to apply an external electric field toincrease or decrease the level of "doping" - that is, theconcentration of mobile electrons inthe material - and see how this affects the ability of the material to carrycurrent.
But to do this in copper-oxide (cuprate) superconductors, one needsextremely thin films of perfectly uniform composition - and electric fieldsmeasuring more than 10 billion volts per meter. (For comparison, the electricfield directly under a power transmission line is 10 thousand volts per meter.)
Bozovic's group has employed a technique called molecular beam epitaxy(MBE) to uniquely create such perfect superconducting thin films one atomiclayer at a time, with precise control of each layer's thickness. Recently,they've shown that in such MBE-created films even a single cuprate layer canexhibit undiminished high-temperature superconductivity.*
Now, they've applied the same technique to build ultrathinsuperconducting field effect devices that allow them to achieve the chargeseparation, and thus electric field strength, for these critical studies.
These devices are similar to the field-effect transistors (FETs) thatare the basis of all modern electronics, in which a semiconducting materialtransports electrical current from the "source" electrode on one endof the device to a "drain" electrode on the other end.
FETs are controlled by a third electrode, called a "gate,"positioned above the source-drain channel - separated by a thin insulator -which switches the device on or off when a particular gate voltage is appliedto it.
But because no known insulator could withstand the high fields requiredto induce superconductivity in the cuprates, the standard FET scheme doesn'twork for high-temperature superconductor FETs. Instead, the scientists usedelectrolytes, liquids that conduct electricity, to separate the charges.
In this setup, when an external voltage is applied, the electrolyte'spositively charged ions travel to the negative electrode and the negativelycharged ions travel to the positive electrode. But when the ions reach theelectrodes, they abruptly stop, as though they've hit a brick wall.
The electrode "walls" carry an equal amount of oppositecharge, and the electric field between these two oppositely charged layers canexceed the 10 billion volts per meter goal.
The result is a field effect device in which the critical temperatureof a prototype high-temperature superconductor compound(lanthanum-strontium-copper-oxide) can be tuned by as much as 30 degreesKelvin, which is about 80 percent of its maximal value - almost ten times morethan the previous record.
The scientists have now used this enhanced device to study some of thebasic physics of high-temperature superconductivity.
One key finding: As the density of mobile charge carriers isincreased, their cuprate film transitions from insulating to superconductingbehavior when the film sheet resistance reaches 6.45 kilo-ohm. This is exactlyequal to the Planck quantum constant divided by twice the electron chargesquared - h/(2e)2.
Both the Planck constant and electron charge are "atomic"units - the minimum possible quantum of action and of electric charge,respectively, established after the advent of quantum mechanics early in thelast century.
"It is striking to see a signature of such clearlyquantum-mechanical behavior in a macroscopic sample (up to millimeter scale)and at a relatively high temperature," Bozovic said. Most people associatequantum mechanics with characteristic behavior of atoms and molecules.
This result also carries another surprising message. While it has beenknown for many years that electrons are paired in the superconducting state,the findings imply that they also form pairs (although localized and immobile)in the insulating state, unlike in any other known material.
That sets the scientists on a more focused search for what gets theseimmobilized pairs moving when the transition to superconductivity occurs.
Superconducting FETs might also have direct practical applications.Semiconductor-based FETs are power-hungry, particularly when packed verydensely to increase their speed. In contrast, superconductors operate with noresistance or energy loss. Here, the atomically thin layer construction is infact advantageous - it enhances the ability to control superconductivity usingan external electric field.
"This is just the beginning," Bozovic said. "We stillhave so much to learn about high-temperature superconductors. But as wecontinue to explore these mysteries, we are also striving to make ultrafast andpower-saving superconducting electronics a reality."
Coauthors on the paper include: I. Bozovic, A. Bollinger, J. Yoon, and J. Misewich from Brookhaven Lab and G.Dubuis and D. Pavuna from Ecole Polytechnique Federale deLausanne
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