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Physics professor probes superconductivity
When Eric Hudson was introduced to high-temperature superconductivity as a graduate student, it was still, so to speak, a hot topic.

The phenomenon, discovered in the 1980s, reflects the fact that if you develop the right types of compounds, you can create electrical conductors that are completely resistance-free at temperatures well above the threshold for conventional superconductors.

"With conventional systems, you get to about 25 degrees Kelvin [-415 F] and then plateau," says Hudson, now the Class of 1958 Assistant Professor of Physics at MIT. "With high-temperature superconductivity, you were suddenly at 90 degrees Kelvin."

That figure is well above the mark at which nitrogen gas turns liquid. This meant you could create devices like the high-powered electromagnets used in many MRI scanners without having to use costly liquid helium to cool the magnets' coils to superconducting temperatures. (Helium, which liquefies at a hyper-frigid 4 degrees above absolute zero, is a must for conventional superconducting devices.)

More exciting yet, the discovery seemed to signal that room-temperature superconductivity was on its way. This triggered claims that problems like electricity line -losses--the often-hefty amount of power lost to resistance in electrical transmission networks--would soon -disappear.

But tough technological hurdles dampened hopes of a resistance-free electrical grid. And for physicists like Hudson, the prospect of figuring out how high-temperature superconductivity (HTS) works at the scale of electrons and protons also faded.

"Initially, a ton of people rushed into the field," he notes. "But in the late 1990s, a lot of them got fed up and left."

Hudson was one of them, switching to another challenging physics problem. But the HTS issue continued to lure him, and after two years he resumed his studies of the phenomenon.

Why? Basically because it's so compelling. "It's a very difficult problem," he notes, "and I feel that when we do understand it, that will open up a whole new world, not only in superconductivity but in related systems."

Hudson has probably helped hasten that day. He's an expert in scanning tunneling microscopy, which is based on the stunning fact that by bringing the right type of tiny metal tip within a few atoms' width of a surface, and generating a voltage between the tip and that surface, you can actually map its individual atoms. (To get a notion of the length scales he's dealing with, consider that an atom of copper--a standard component of many HTS compounds--is to a ping pong ball as the ball is to the moon.)

Now, Hudson and his co-workers have contributed an advance in the technology that promises new progress in unveiling HTS's secrets. Given the all-but infinitesimal size of individual atoms, tunneling microscope users until recently haven't been able to track individual atoms within a compound as they lowered the compound's temperature. By tweaking the makeup of a key part of their microscope, though, the MIT group has solved the problem. That matters, says Hudson.

"If you want to understand what's going on as a function of temperature in these materials," he explains, "you need to be able to follow individual atoms."

The group's recent studies have already undercut one popular theory about the changes that affect HTS materials as their temperature falls. That finding may in turn clear the way for competing hypotheses.

Such advances, and the fact that organizations such as the U.S. Department of Energy are again giving priority to the HTS phenomenon, show the field is regaining its momentum. Yet while the world's first-ever HTS electrical transmission line--an underground Albany-area cable cooled by liquid nitrogen--went live on test basis last year, the steps forward so far don't mean dramatic new applications are imminent.

On the other hand, Hudson does think basic research on the HTS phenomenon is making real head way. "Things are at a point now," he says, "where I believe we'll solve this within my professional lifetime."

Source: MIT (Reprinted from MIT SPECTRVM, by Richard Anthony)
Via: http://www.physorg.com/news110726111.html
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New research sheds light on shimmering superconductivity and the courtship of electrons

In their normal state, electrons repel each other because of their charge, but in the state of superconductivity, electrons pair up. John Schlueter, a chemist from the U.S. Department of Energy's Argonne National Laboratory, collaborated with a team of researchers from the University of Oxford to better understand how this unlikely courtship occurs.

Their recent research appears in the October 4 issue of Nature and finds that a form of shimmering superconductivity exists at temperatures well above that at which ordinary superconductivity is destroyed. This electron courtship is characterized by a tension between the conflicting urges for electrons to pair up (which leads to superconductivity) and to repel each other (which leads to insulating behavior).

Superconductors conduct electricity with absolutely no resistance when cooled below a certain critical temperature, Tc. “Superconductivity already has important applications and many more uses are possible if critical temperatures are high enough,” Schlueter explained.

Much research over the past decade has focused on inorganic cuprate superconductors. Although molecular superconductors currently have maximum Tcs near 10 K (nearly an order of magnitude lower than the cuprates), they have many features that make them ideal for the study of the fundamental properties of superconductivity. In the organic materials, lower temperatures and magnetic fields are required to reach the boundaries between superconducting and normal states, thus making these experiments much easer to perform in a laboratory.

Although such shimmering superconductivity above the usual temperature barrier has previously been observed in cuprate materials, this is the first time it has been seen in an extremely clean and well controlled system that doesn't have to be chemically doped to produce superconductivity. This means that scientists can be sure that the effect is not associated with impurities. In fact, the team believes that such an effect should be found in all superconductors in which conflicting interactions are finely balanced. This is an important step forward in the quest to understand superconductivity in what are known as "highly correlated" materials: the superconductors of the future.

The Argonne group has long been recognized as an international leader in the discovery and crystallization of high quality crystals of molecular superconductors. “We use an electrocrystallization technique both as a discovery tool and a means to enable sophisticated measurements aimed at unraveling some of the outstanding mysteries of superconductivity,” Schlueter explained. This research was performed on a superconducting material discovered by the Argonne group in 1990, addresses a longstanding question relating to the pairing of electrons in superconducting materials. The study identifies similarities between the high and low temperature superconductors.

The discovery was made by Moon-Sun Nam in collaboration with Arzhang Ardavan and Stephen Blundell in Oxford University's Department of Physics, using crystals grown by John Schlueter. The team exploited a particularly sensitive probe of superconducting fluctuations called the "vortex-Nernst effect". This effect provides a way of detecting that superconducting vortices are present, even when zero electrical resistance (the characteristic of traditional superconductivity) is not exhibited.

Source: Argonne National Laboratory
Via: http://www.physorg.com/news110726933.html