Superconductivity in orbit: Scientists find new path to loss-free electricity

Feb 13, 2014
These images show the distribution of the valence electrons in the samples explored by the Brookhaven Lab collaboration -- both feature a central iron layer sandwiched between arsenic atoms. The tiny red clouds (more electrons) in the undoped sample on the left (BaFe2As2) reveal the weak charge quadrupole of the iron atom, while the blue clouds (fewer electrons) around the outer arsenic ions show weak polarization. The superconducting sample on the right (doped with cobalt atoms), however, exhibits a strong quadrupole in the center and the pronounced polarization of the arsenic atoms, as evidenced by the large, red balloons. Credit: Brookhaven National Lab

(Phys.org) —Armed with just the right atomic arrangements, superconductors allow electricity to flow without loss and radically enhance energy generation, delivery, and storage. Scientists tweak these superconductor recipes by swapping out elements or manipulating the valence electrons in an atom's outermost orbital shell to strike the perfect conductive balance. Most high-temperature superconductors contain atoms with only one orbital impacting performance—but what about mixing those elements with more complex configurations?

Now, researchers at the U.S. Department of Energy's Brookhaven National Laboratory have combined atoms with multiple orbitals and precisely pinned down their electron distributions. Using advanced electron diffraction techniques, the scientists discovered that orbital fluctuations in iron-based compounds induce strongly coupled polarizations that can enhance electron pairing—the essential mechanism behind superconductivity. The study, set to publish soon in the journal Physical Review Letters, provides a breakthrough method for exploring and improving superconductivity in a wide range of new materials.

"For the first time, we obtained direct experimental evidence of the subtle changes in electron orbitals by comparing an unaltered, non-superconducting material with its doped, superconducting twin," said Brookhaven Lab physicist and project leader Yimei Zhu.

While the effect of doping the multi-orbital barium iron arsenic—customizing its crucial outer electron count by adding cobalt—mirrors the emergence of in simpler systems, the mechanism itself may be entirely different.

"Now superconductor theory can incorporate proof of strong coupling between iron and arsenic in these dense interactions," said Brookhaven Lab physicist and study coauthor Weiguo Yin. "This unexpected discovery brings together both orbital fluctuation theory and the 50-year-old 'excitonic' theory for high-temperature superconductivity, opening a new frontier for condensed matter physics."

Atomic Jungle Gym

Imagine a child playing inside a jungle gym, weaving through holes in the multicolored metal matrix in much the same way that electricity flows through materials. This particular kid happens to be wearing a powerful magnetic belt that repels the metal bars as she climbs. This causes the jungle gym's grid-like structure to transform into an open tunnel, allowing the child to slide along effortlessly. The real bonus, however, is that this action attracts any nearby belt-wearing children, who can then blaze through that perfect path.

Flowing electricity can have a similar effect on the atomic lattices of superconductors, repelling the negatively charged valence electrons in the surrounding atoms. In the right material, that repulsion actually creates a positively charged pocket, drawing in other electrons as part of the pairing mechanism that enables the loss-free flow of current—the so-called excitonic mechanism. To design an atomic jungle gym that warps just enough to form a channel, scientists audition different combinations of elements and tweak their quantum properties.

"High-temperature copper-oxide superconductors, or cuprates, contain in effect a single orbital and lack the degree of freedom to accommodate strong enough interactions between electricity and the lattice," Yin said. "But the barium iron arsenic we tested has multi-orbital electrons that push and pull the lattice in much more flexible and complex ways, for example by inter-orbital electron redistribution. This feature is especially promising because electricity can shift arsenic's electron cloud much more easily than oxygen's."

In the case of the atomic jungle gym, this complexity demands new theoretical models and experimental data, considering that even a simple lattice made of north-south bar magnets can become a multidimensional dance of attraction and repulsion. To control the doping effects and flow of electricity, scientists needed a window into the orbital interactions.

Tracking Orbits

"Consider measuring waves crashing across the ocean's surface," Zhu said. "We needed to pinpoint those complex fluctuations without having the data obscured by the deep water underneath. The waves represent the all-important electrons in the outer orbital shells, which are barely distinguishable from the layers of inner electrons. For example, each barium atom alone has 56 electrons, but we're only concerned with the two in the outermost layer."

The Brookhaven researchers used a technique called quantitative convergent beam (CBED) to reveal the orbital clouds with subatomic precision. After an electron beam strikes the sample, it bounces off the charged particles to reveal the configuration of the atomic lattice, or the exact arrays of nuclei orbited by electrons. The scientists took thousands of these measurements, subtracted the inner electrons, and converted the data into probabilities—balloon-shaped areas where the valence electrons were most likely to be found.

Shape-Shifting Atoms

The researchers first examined the electron clouds of non-superconducting samples of barium iron arsenic. The CBED data revealed that the arsenic atoms—placed above and below the iron in a sandwich-like shape (see image)—exhibited little shift or polarization of valence electrons. However, when the scientists transformed the compound into a superconductor by doping it with cobalt, the electron distribution radically changed.

"Cobalt doping pushed the orbital electrons in the arsenic outward, concentrating the negative charge on the outside of the 'sandwich' and creating a positively charged pocket closer to the central layer of iron," Zhu said. "We created very precise electronic and atomic displacement that might actually drive the critical temperature of these superconductors higher."

Added Yin, "What's really exciting is that this electron polarization exhibits strong coupling. The quadrupole polarization of the iron, which indicates the orbital fluctuation, couples intimately with the arsenic dipole polarization—this mechanism may be key to the emergence of high-temperature superconductivity in these iron-based compounds. And our results may guide the design of new materials."

This study explored the orbital fluctuations at room temperature under static conditions, but future experiments will apply dynamic diffraction methods to super-cold samples and explore alternative material compositions.

Explore further: How to make graphene superconducting

Related Stories

How to make graphene superconducting

Feb 11, 2014

Whenever a new material is discovered, scientists are eager to find out whether or not it can be superconducting. This applies particularly to the wonder material graphene. Now, an international team around ...

Giant atom eats quantum gas

Oct 31, 2013

A team of experimental and theoretical physicists from the University of Stuttgart studied a single micrometer sized atom. This atom contains tens of thousands of normal atoms in its electron orbital. These ...

Superconductivity's third side unmasked

Jun 17, 2011

The debate over the mechanism that causes superconductivity in a class of materials called the pnictides has been settled by a research team from Japan and China. Superconductivity was discovered in the pnictides ...

Optimizing electronic correlations for superconductivity

Nov 18, 2013

(Phys.org) —The decadeslong effort to create practical superconductors moved a step forward with the discovery at Rice University that two distinctly different iron-based compounds share common mechanisms for moving electrons.

Recommended for you

WEGA fusion experiment passed on to the USA

14 hours ago

The small WEGA fusion device at Max Planck Institute of Plasma Physics (IPP) in Greifswald is being handed over to the University of Illinois in Urbana-Champaign. The "Wendelstein-Experiment in Greifswald ...

Researchers design plasmonic cavity-free nanolaser

15 hours ago

(Phys.org) —A team of researchers at Imperial College in London has designed a new type of laser, one that could be made much smaller than today's models because it would be cavity-free. In their paper ...

Uncovering the forbidden side of molecules

Sep 21, 2014

Researchers at the University of Basel in Switzerland have succeeded in observing the "forbidden" infrared spectrum of a charged molecule for the first time. These extremely weak spectra offer perspectives ...

User comments : 12

Adjust slider to filter visible comments by rank

Display comments: newest first

Nestle
1 / 5 (1) Feb 13, 2014
The iron arsenides have low temperature of superconductive onset anyway (9–25 K). The really interesting superconductor research is done outside of mainstream science already. It becomes really hot - not just literally. If the physicists do really want to understand, how the HT superconductivity works, they should learn it from master illustrative examples of it, not from rather complex and subtle iron pnictides.

If you take a look at Joe Eck's superconductors, then you will realize the trick, on which it's based on at the first sight.
Macksb
1 / 5 (1) Feb 13, 2014
An Art Winfree pattern of coupled oscillators. As I have predicted in many prior physorg posts.
Teemu
not rated yet Feb 14, 2014
Nestle,

Why does Joe Eck only manage to increase the critical temperature but not the volume fraction, the proportion of the sample that is superconductive?

The critical temperature keeps on rising and rising, now supposedly well beyond room temperature, but the fraction of supposedly superconductive material stays small. If he is developing his materials systematically based on somekind of insight, the volume fraction should also go up.

If the activity on the MT curve is measurement error, or one of the other possible phenomena than superconducting transition, "increasing the critical temperature" obviously is considerably easier than increasing the yield, because you can keep trying to find this non-sc phenomena or error on the data from the higher temperatures, but obviously you can't you can't increase the volume fraction...

There is plenty of articles, discussion in the internet, about what other stuff than superconductivity can cause interesting looking stuff on the M-T curve
Teemu
not rated yet Feb 14, 2014


Maybe this is the reason why the yield isn't going up, but the temperature keeps going up.

If you don't have real superconductor, it is much easier to try to find some random positive momentum on the M-T curve at higher and higher temperatures than increase the yield...'

ttp://arxiv.org/ftp/cond-mat/papers/0608/0608368.pdf

However,signals from non-superconducting inhomogeneous samples can easily mimic superconducting signals, due to a redistribution of current flow caused, for example, by differing temperature-dependent resistivity of the different phases (a positive-negative result)
Osteta
Feb 14, 2014
This comment has been removed by a moderator.
Osteta
Feb 14, 2014
This comment has been removed by a moderator.
Osteta
Feb 14, 2014
This comment has been removed by a moderator.
Osteta
Feb 14, 2014
This comment has been removed by a moderator.
Osteta
Feb 14, 2014
This comment has been removed by a moderator.
Macksb
not rated yet Feb 14, 2014
Thanks for your first comment above, directed to my Art Winfree post. The article explains the many factors that cause oscillations to couple in this particular instance. Simply put, there is teamwork, flexibility and coordination at every level: atoms, atoms to electrons, electrons. A complex synchrony emerges, as shown in the picture and described in the article. Strong coupling, per the authors. Of periodic oscillations. Art Winfree.
Osteta
Feb 14, 2014
This comment has been removed by a moderator.
Macksb
not rated yet Feb 15, 2014
Your disagreement is with the authors, Osteta, not with me. "Strong coupling" is from their text, as are the other points I cited in my response.

If you wish to disagree with me, as opposed to the authors, you should focus on my reference to Art Winfree and his law of coupled oscillators. I am unique in applying Winfree's law to physics, and superconductivity in particular. The mathematical underpinning of his law has been tested by many (Kuramato, Strogatz, Mirollo) and confirmed. The application of his law to biology, which he initiated, has similarly been confirmed many times over. E.g., by Ermentrout. But it has not been applied to physics, except by me, and the applications I propose are sweeping: namely, that Winfree's law can explain all phases of matter, including superconductivity. If you wish to disagree with me, this is the target at which you should aim. Fire when ready.
Nestle
not rated yet Feb 15, 2014
Nobody doubts that the coupled oscillators do apply to many cases in the nature in the same way, like the spontaneous symmetry breaking or wave interference does apply to many cases in the nature. Their mathematical underpinning has been tested many as well. But what these concepts have to do in superconductivity and how they can explain, what happens there? This is the question.
that Winfree's law can explain all phases of matter, including superconductivity
In this law the therefore superconductivity wouldn't differ from another phases of matter.This is just another problem - who is everywhere, remains nowhere.
Teemu
not rated yet Feb 15, 2014
Or maybe there is no superconductive parts in Joe Eck's samples, but rather he just has a current redistribution typical for highly inhomogeneous samples, and he thinks that is superconductivity

http://arxiv.org/...8368.pdf

However,signals from non-superconducting inhomogeneous samples can easily mimic superconducting signals, due to a redistribution of current flow caused, for example, by differing temperature-dependent resistivity of the different phases (a positive-negative result)

http://iopscience...0412.pdf

Investigation of the positive moments on the M-T curve of a YBCO film measured by using zero-field cooling

The experimental results have shown that there are positive magnetic moment and positive peak on the M-T curve. We have proven that these anomalous behaviours are due to measurement error, but not phase transition.
Macksb
not rated yet Feb 15, 2014
Thanks for your question, Nestle: How can Winfree's law of coupled oscillators explain superconductivity? Study the superconductivity described in this Physorg article, particularly the picture on the right (doped, superconducting). That is a 5 oscillator system: one in the middle of the square, four on the corners of the square. Per Winfree, if a 5 oscillator system synchronizes, it will express itself only in certain precise ways, which he specified. A horse and rider is a five oscillator system (rider plus 4 horse legs), which can be expressed in certain gaits of the horse and certain up and down oscillations of the rider. All 5 sync their oscillations.

In the above article, the "rider" is in the center of the square. Sync 5 ways.

The perovskite structure of the cuprate HTS materials is also a 5 oscillator system: a "rider" (a big atom) above the cuprate plane (4 coppers) in which superconductivity breaks out. Sync 5 ways.

Electrons then sync their oscillations 2 or 4 ways
Nestle
not rated yet Feb 15, 2014
rather he just has a current redistribution typical for highly inhomogeneous samples, and he thinks that is superconductivity
Of course his work deserves thorough replication. But Eck is able to provide whole set of samples with "current redistribution" gradually rising across large temperature interval. As with cold fusion, we can imagine dozens of reasons for why these experiments shouldn't work or to provide false positive signals. But without experiments it's just theorizing and we will never get the truth. BTW The Joe Eck works are often plagiarized, which could provide a clue for you. He has no problem with lack of interest about his work, on the contrary.
Macksb
not rated yet Feb 15, 2014
BCS theory of low-temp superconductivity also follows Winfree's law. Per BCS, phonons (lattice oscillations) sync the oscillations of electrons, creating Cooper pairs of electrons. In Cooper pairs, both oscillations of Electron A, orbit and spin, sync exactly anti-synchronously with the orbit and spin of Electron B. Locked. Per Winfree's law, or my terms, this 3 oscillator system (phonon plus 2 electrons) creates a 2 oscillator system (a Cooper pair). When oscillations sync, Winfree's law is the explanation.

The point at which synchrony breaks out is the transition temp. Non-linear. Lower temp means lower frequency of oscillations, which helps oscillations sync. High temp supers involve larger, more complex synchronized systems than simple BCS model--but Winfree's law explains both.

Winfree's law also explains magnesium diboride. Two rings of six oscillators each, interacting. The analog is the six legs of insects which, as you know, move only in certain specific ways.

Teemu
not rated yet Feb 15, 2014
When the signal is weak, barely above noise, it can be really easy to find what you want to find, to see what you want to see. Depending on how you choose the section of the data, and how you select the axis, you can make the results look much more impressive than they are.

Maybe he just looks there where he expects the results, and because of high noise, it is easy to see something where you expect it to be, that is the way confirmation bias works.

Those plagiarized papers are from Third World universities. The high temperature cuprate results of Bednorz and Muller were quickly repeated and improved upon by other First World scientists. Of course I'm willing to agree that he has no problem with lack of interest about his work, so you could stop spamming every superconductivity article with this stuff.