SuperConductivity: Research & Findings & Thoughts

[MGmirkin]

Well, yes, the atmosphere is generally a dielectric (an insulator). Lightning is dielectric breakdown due to electrical field strength (opposing clouds of charges rooted in the cloud and in the Earth; the voltage or electric field strength falls under the purview of electrostatics, I think). Once the charges start moving, we're dealing with an electric current (falling under the purview of electrodynamics). Once the lightning quenches, the atmosphere eventually goes back to a more neutral state acting as an insulator (dielectric) again. That's more or less the self-repairing leaky-capacitor aspect of the Earth. IE, the atmosphere is USUALLY an insulator, unless electric field strength is sufficient to start charges flowing, at which point the atmosphere gets a bit ionized (conductive), a discharge happens (sometimes several discharges happen once one or more conductive paths are opened up), and then the ionized channel dissipates, neutrals rush back in, and the "leak" in the capacitor's dielectric is fixed.

In a way it is possible to say the reverse of diamagnetics. Also a insulator (only of magnetic fields as opposed to the shielding of electric fields by the dielectric). But what creates the conductive path for the discharge?

I think an insulator generally stops the flow of an electric current, which is different from an electric field (unless I'm mistaken). Best to be careful with terms. The electric field is essentially the electric potential between differing clouds of charge that want to neutralize. It's kind of like having a bunch of positively charged rocks piling up on top of a hill. As some point the pile gets so large that it becomes unstable and an avalanche happens. The pile at the top of the hill, the hill itself and the lack of a pile at the bottom of the hill (somewhere for the pile to go) sets up a certain potential for movement of the pile of charged stuff. That's essentially the electric field in the analogy. Once the pile gets large enough on top of the hill, such that the hill isn't sufficient to hold any more, the pile starts shifting under its won weight and an avalanche happens. The avalanche of the "charged" stuff rolling down the hill equates to the flowing electric current, with the hill and gravity being the analogous "electric field."

Perhaps not the best example, but hopefully illustrative?

IE, the electric field is a result of electrostatics (stationary charges; the pile of rocks at the top of the hill, andthe lack of rocks at the bottom of the hill). The electric current is a a motion of the charged particles due to the potential energy of the clouds of charged particles being converted into kinetic energy. At that point it falls under electrodynamics or the actions of particles in motion with respect to each other.

As to what causes the breakdown, it's hard to say, it seems to me like at some point the electric field strength becomes so great that it forces whatever charged particles are available to start moving through the dielectric. It may be that the motion causes collisions that knock around other atoms to he point of ionization, and you get a runaway breakdown effect where this flow start ionizing more material at the front, kind of like an electric shockwave ionizing the otherwise neutral atmosphere as it goes, and creating a channel through which the charges can flow. All of this happens rather quickly once it starts. As show in high-speed footage of lightning strikes...

In an electric field, positive charges in a current will tend to flow one way, while negative charges will tend to flow the other.

(Which Way Does the "Electricity" Really Flow?)
http://amasci.com/amateur/elecdir.html

So, I'm assuming that once the electrical leader stroke ionizes the material, the electrons knocked loose go one way, and th positively charged ions will tend to go the other...

So, yeah, that's how I perceive the interaction to go. Feel free to correct me, anyone, if I've buggered anything up.

Regards
~Michael Gmirkin

[junglelord]

Magnetism and Superconductivity Observed to Exist in Harmony

Physicists at Los Alamos National Laboratory, along with colleagues at institutions in Switzerland and Canada, have observed, for the first time in a single exotic phase, a situation where magnetism and superconductivity are necessary for each other's existence.

Physicists have seen the battle for supremacy between the competing states of magnetism and superconductivity as one in which no truce could be struck. This perplexing dilemma has thwarted scientists' quest for the resistance-free flow of electrons, and, with it, the vast potential in energy savings that superconductivity holds for ultra-efficient power transmission, magnetic resonance imaging (MRI) technology, and other applications.

In the current online advance edition of the journal Science, the international team of scientists reports the simultaneous observation of both states in a compound containing the elements cerium, cobalt, and indium (CeCoIn5) at a temperature close to absolute zero about 460 degrees below zero, Fahrenheit. Coauthor Andrea Bianchi, who is now based at the University of Montreal, was the first to see this phase at Los Alamos National Laboratory in 2003.

"This coexistence is an exotic superconducting state that has not been observed in any other superconducting material," said Los Alamos scientist Roman Movshovich, one of the paper's authors. "It shows a very strong link between superconductivity and magnetism."

Scientists understand superconductivity as a phenomenon that occurs when electrons spinning in one direction form pairs with electrons spinning in the opposite direction, usually at very low temperatures. These pairs, in turn, combine with each other to form a new superconducting state of matter where electrons move resistance-free through the material. Superconductivity is a manifestation of interactions that take place between few particles (electrons and atoms) that reveal themselves on a macroscopic scale, in samples that we can see and touch. Magnetism, where electrons' magnetic spins are fixed in space in an orderly fashion, requires participation of the same electrons and therefore generally competes with superconductivity.

But why, in this particular case, magnetism and superconductivity appeared at the same time in the same compound is still a mystery. "It's not clear what the origin of this state is, or what creates or modifies it," Movshovich said.

If physicists can work out how magnetism figures into the origin of superconductivity, which is currently only possible at temperatures hundreds of degrees below zero, they will be one step closer to the "holy grail" of modern condensed matter physics: superconductivity at temperatures high enough to eliminate expensive cooling liquids such as nitrogen and helium.

"It's really a question of the chicken and the egg," said coauthor Eric Bauer of Los Alamos. "Does superconductivity need magnetism in this state, or does magnetism need superconductivity?"

The scientists applied a high magnetic field to a crystal of this compound synthesized by Bauer and his colleague John Sarrao at Los Alamos, suppressing its superconductivity. They found that, as a consequence, the crystal also lost its magnetism. This evidence suggests that without superconductivity, magnetism is not possible in CeCoIn5. The converse, however, isn't necessarily true.

It appears that superconductivity could occur even in the absence of magnetism, either at lower magnetic field, or at a slightly higher temperature, Bauer said.

The extraordinary "cleanliness" inherent in the quality of the crystal grown in the Materials Physics and Applications division at Los Alamos was one of the reasons the team was able to coax these coupled states from the compound, Movshovich said. The importance of cleanliness was demonstrated in one of this team's previous studies where minute amount of impurities were introduced on purpose, and such samples did not display this fragile superconducting/magnetic state.

With these "clean" crystals, a group led by Michel Kenzelmann of the Paul Scherrer Institute and the Swiss Federal Institute of Technology, both in Switzerland, probed the compound with a beam of neutrons to elucidate its physical properties. Though neutrons don't carry a charge like electrons and protons do, they still have a magnetic spin that interacts with magnetic order inside a compound. Based on the direction of the neutrons when scattered from the crystal, the team was able to deduce the magnetic structure of the coupled magnetic/superconducting state.

CeCoIn5 is what's known as a heavy fermion material because at low temperatures its electrons act as if they are much heavier than they really are, due to interactions with magnetic ions (Ce in this case) in the lattice structure of the material. And although the experiments in this latest round of research took place at low temperatures, electrons in both heavy fermion compounds and high-temperature superconductors are believed to pair up and move in much the same way, and the fundamental knowledge obtained will contribute to our general understanding of the superconducting phenomena. The team's findings are likely to trigger further studies in similar compounds.

"This is a new paradigm for understanding the interplay between magnetism and superconductivity," Bauer said. "It could help us find the basis for understanding unconventional (high-temperature) superconductivity."

Provided by Los Alamos National Laboratory


http://www.physorg.com/news139159195.html

[seasmith]

~

Europium found to be a superconductor

James S. Schilling, Ph.D., professor of physics in Arts & Sciences at Washington University in St. Louis, and Mathew Debessai, Ph.D., — his doctoral student at the time — discovered that europium becomes superconducting at 1.8 K (-456 °F) and 80 GPa (790,000 atmospheres) of pressure, making it the 53rd known elemental superconductor and the 23rd at high pressure.

Of the rare earths, europium is most likely to lose its magnetism under high pressures due to its electronic structure. In an elemental solid almost all rare earths are trivalent, which means that each atom releases three electrons to conduct electricity.

Scientists do not have enough theoretical understanding to be able to design a combination of elements that will be superconductors at room temperature and pressure. Schilling's result provides more data to help refine current theoretical models of superconductivity.

Schilling will present his findings at the 22nd biennial International Conference on High Pressure Science and Technology in July 2009 in Tokyo, Japan.
http://www.nanowerk.com/news/newsid=10666.php

[seasmith]

Light Touch Transforms Material into Superconductor

“We have shown that the non-superconducting state and the superconducting one are not that different in these materials, in that it takes only a millionth of a millionth of a second to make the electrons ‘synch up’ and superconduct,” said Cavalleri. “This must mean that they were essentially already synched in the non-superconductor, but something was preventing them from sliding around with zero resistance. The precisely tuned laser light removes the frustration, unlocking the superconductivity.”

In the journal Science, they describe how a strong infrared laser pulse was used to perturb the positions of some of the atoms in the material. The compound, held at a temperature just 20 degrees above absolute zero, almost instantaneously became a superconductor for a fraction of a second, before relaxing back to its normal state.

http://www.photonics.com/Article.aspx?A ... Newsletter


SC theory as discussed above, postulates the "expulsion" of magnetism, an (imposed) crystalgraphic molecular and Cooper pairing of electrons for Type II superconductivity to occur; but now that 'light' is thrown into the mix, more basic questions are prompted such as:
the nature of 'charge' being conducted, the spin/orbital character of Cooper pairing,
what is most fundamentally aligned in a 'crystal' structure,
when do EM flux-fields become cylinders/tubes/lines of propagating charge
and finally what is the shape of a shift from E to M or M to E ?

Unlike wavefronts of light, which are hundreds of nanometers apart (a distance called the wavelength), the wavelengths of electrons are measured in picometers (trillionths of a meter), which make them excellent for imaging tiny objects such as atoms because of their comparable dimensions.

"Magnetism, at its most fundamental, results from charges spinning and orbiting," McMorran said. "So an electron beam that itself carries angular momentum makes a good tool for probing magnetic materials."

http://www.photonics.com/Article.aspx?A ... Newsletter


~ At what scale does spin become orbit,
electric or photonic ?