Constructive conflict in the superconductor

Aug 17, 2012
Constructive conflict in the superconductor
Researchers at the Max Planck Institute for Solid State Research have discovered charge density waves in ceramic yttrium and neodymium barium cuprates. They form above the temperature at which the material becomes superconducting and thus loses its electrical resistance, slightly distorting the crystal lattice, as indicated in a layer of the crystal lattice by the irregular distances between the atoms (blue spheres). The superconductivity competes with the charge density waves, and it is probably down to a coincidence that superconductivity prevails at a certain temperature. Credit: Daniel Pröpper/MPI for Solid State Research

Whether a material conducts electricity without losses is not least a question of the right temperature. In future it may be possible to make a more reliable prediction for high-temperature superconductors. These materials lose their resistance if they are cooled with liquid nitrogen, which is relatively easy to handle.

An international team, in which physicists of the Max Planck Institute for Solid State Research in Stuttgart played a crucial role, has now discovered that this form of superconductivity competes with charge , i.e. with a periodically fluctuating distribution of the charges. Since the physicists did not previously take account of this competition in their models, their calculations of the transition temperature, where superconductivity sets in, remained inaccurate. In further work, the researchers at the Stuttgart Max Planck Institute have gained insights into how superconducting materials interact with magnetic ones. They observed that the affect crystal vibrations to a greater extent than was to be expected. This effect could help to control material properties such as superconductivity or .

If electricity from high-power or even large-scale solar parks in the Sahara is to be distributed to consumers in Germany in future, quite a bit of energy will be lost in the long power lines. Superconducting cables could prevent this if cooling them does not consume more energy than they help to save. Bernhard Keimer and his colleagues at the Max Planck Institute for Solid State Research in Stuttgart want to identify materials that deserve the name high-temperature superconductor both in practical terms and also in terms of our usual perception of temperature. To do this they first have to understand how superconductivity works in these materials and how it can be influenced; these materials are known as high-temperature superconductors, even though they lose their resistance at temperatures which make a Siberian winter seem almost mild. The Stuttgart-based physicists have now taken a further step down this road in two current publications.

According to one of their discoveries we can probably consider ourselves lucky that high-temperature superconductivity - a property which remains promising despite its present disadvantages - exists at all. "It is obviously down to a fortunate coincidence," says Bernhard Keimer, Director at the Stuttgart Institute. This is at least suggested by the observations of the international team that includes not only Bernhard Keimer and his colleagues, but also scientists at the Politecnico di Milano, the European Synchrotron Radiation Facility Grenoble, the University of British Columbia in Canada and further research institutions.

Superconductivity beats the charge density waves in a close competition

The researchers discovered that the superconductivity in one type of copper oxide ceramic competes with a state in which a charge density wave forms. Physicists have known about such charge density waves for decades from two-dimensional materials such as the niobium selenides, for example. Here, the conduction electrons do not distribute uniformly across the crystal like in a metal. On the contrary, they form a regular pattern of regions in which they concentrate to a greater or lesser extent.

"We did not expect the charge density waves in the superconducting cuprates, because they destroy the superconductivity," says Bernhard Keimer. Instead of concentrating at regular intervals to a greater or lesser extent, the electrons in superconductors join up to form Cooper pairs which can slip through a crystal with zero resistance. Accordingly, the researchers observed the charge patterns only above the transition temperature, the temperature at which the material becomes superconducting.

The regions where charge density waves formed initially expanded as the researchers cooled the material down to the transition temperature, however. As soon as they reached the transition temperature at minus 213 degrees Celsius, the charge density waves suddenly disappeared and superconductivity prevailed.

"Superconductivity only just prevailed in this competition," explains Bernhard Keimer. "If the advantages were distributed slightly differently, there would possibly be no superconductivity at all."

Charge density waves explain why calculated transitions temperatures were too high

The team of researchers tracked down the charge density waves by scanning yttrium and neodymium barium cuprates of the composition (Y,Nd)Ba2Cu3O6+x with the aid of resonant X-ray diffraction. This provided them with exclusive information on the electrons which found it hard to decide whether they wanted to form a wave or look for a partner so that, together, they could slip more easily through their crystal. The physicists in Bernhard Keimer's group are now going to perform these measurements on other high-temperature superconductors as well. They want to find out whether all these materials are in electronic competition.

In addition, the researchers want to take account of the conflict between the two electronic states in their theoretical model of superconductivity. "We can already compute the transition temperature of a material quite well with this model, but still end up slightly too high," says Bernhard Keimer. "The competition with the charge density wave explains this discrepancy so that our predictions should become more accurate in the future."

Superconductivity can be affected by magnetism

Charge density waves possibly also explain an observation which his team made recently in a different project. A high-temperature superconductor was also instrumental here. It also was composed of yttrium, barium and copper oxide and is described by the formula YBa2Cu3O7, or YBCO for short. The researchers now combined this ceramic with a magnetic material comprising lanthanum, calcium and manganese oxide, which obeys the formula La2/3Ca1/3MnO3 (or LCMO). They stacked up the two substances to form a superlattice, a sandwich of layers only a few nanometres thick, and they had a clear aim in doing this.

"In the meantime we assume that the Cooper pairs in high-temperature superconductors form due to magnetic interactions," explains Bernhard Keimer. "If this is the case, superconductivity should be affected by magnetism in order to increase the transition temperature." The special form of magnetism in the LCMO may not be suitable for this, however, because this material is ferromagnetic, i.e. the magnetic moments of the individual atoms all align in one direction, as in iron. And this form of magnetism breaks up the Cooper pairs, thus harming the superconductivity, and decreases the transition temperature. This material is good for investigating how the transition temperature reacts to the magnetism, however, and for the detailed basis for its effect.

And indeed the researchers observed what they had expected: in a sandwich with LCMO, the transition temperature of the YBCO decreased, and the decrease was greater the thinner the researchers made the YBCO layers in comparison to the LCMO. Bernhard Keimer and his colleagues now wanted to find out more details of the interactions between the different layers. They specifically wanted to determine how the electronic processes in a layer - the superconductivity on the one hand, and the magnetism on the other - affect the vibrations of the atoms in this layer. call the interaction electron-phonon coupling, where phonon stands for vibration.

The coupling between electrons and vibrations affects material properties

An illustrative description of the mechanism is that the electrons act like springs between the atoms. The state the electrons adopt affects the springiness of the springs and thus their ability to couple vibrations. The electron-phonon coupling is the basis of a few useful . They include the ability of some materials to convert a temperature difference into a voltage, and also conventional superconductivity, where it is the vibrations of the crystal lattice and not the magnetism that bonds the Cooper pairs together. The researchers have investigated the electron-phonon coupling by observing selected vibrations with a Raman spectrometer as they cooled the material sandwich until magnetic order appeared in the LCMO and superconductivity in the YBCO.

According to the measurements made by the researchers in Stuttgart, one vibration of the copper oxide group in the YBCO layer changed its frequency when the superconductivity set in at the . One vibration of the manganese oxide group in the LCMO layer reacted in the same way when the ferromagnetic order formed in the material. "This didn't really surprise us," said Bernhard Keimer. "But we didn't expect that the superconductivity would also affect the vibration of the manganese oxide."

The electron-phonon coupling therefore also makes itself felt across material boundaries, and this occurs not only right on the boundary between the two substances, but in the whole LCMO layer. This is unexpected, because the vibrations deep in the two layers at least are usually as independent as two children playing on adjacent swings. The Stuttgart-based researchers cannot yet completely explain their observations, but they already have some ideas and meanwhile also indications of what could cause the long-range electron-phonon coupling.

Charge density waves explain the long-range electron-phonon coupling

One condition for the cross-boundary coupling is that, right on the boundary, the copper and manganese atoms are bound very strongly to each other via an oxygen atom in each case. This bond acts like a rubber band between two swings. Moreover, the copper and manganese atoms can oscillate with the same frequency so that a vibration of the copper atoms can easily drag along the manganese atoms. Just as two children can only swing with the same rhythm if their swings have the same length, i.e. they swing with the same frequency. And assuming that their two swings are connected to each other with a strong rubber band: one child can only pull the other along if both are sitting on swings of the same length.

After all, one child in such a swing tandem requires powerful pushers in order for the other one to swing along. In the same way, the YBCO-LCMO superlattice requires a strong trigger in order for the manganese atoms to react to the of the copper atoms. If this trigger comes from the electrons, more precisely from the nascent superconductivity, the electron-phonon coupling must be strong. The YBCO-LCMO sandwich fulfils this condition as well. "The fact that the effect remains noticeable in the whole LCMO layer as well is possibly again caused by the charge density waves in the YBCO," explains Bernhard Keimer. "In our current experiments we have also already found indications that the sandwich structure stabilises this competing order."

The long-range electron-phonon coupling in the LCMO-YBCO superlattice is not helpful in driving up the temperature at which the high-temperature superconductor loses its resistance. "But it gives us the opportunity to influence other properties such as thermoelectricity or conventional ," explains Bernhard Keimer. And it increases the understanding of how magnetic and influence each other. This in turn brings the researchers in Stuttgart further towards their ultimate goal: to develop superconductors that can transport in an energy efficient way from wind farms and solar parks to the consumer.

Explore further: CERN: World-record current in a superconductor

Related Stories

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 ...

Secrets behind high temperature superconductors revealed

Feb 22, 2009

(PhysOrg.com) -- Scientists from Queen Mary, University of London and the University of Fribourg (Switzerland) have found evidence that magnetism is involved in the mechanism behind high temperature superconductivity.

In-Plane Spectral Weight Shift of Charge Carriers in YBa2Cu3O6.9

May 01, 2004

The mechanism of high-temperature superconductivity is one of the main unsolved problems in condensed-matter physics. A. V. Boris et al. from Max-Planck-Institut, Germany present their study of YBa2Cu3O6.9 in this week Science issue (Scie ...

New property in warm superconductors discovered

Nov 17, 2010

(PhysOrg.com) -- Led by Simon Fraser University physicist Jeff Sonier, scientists at TRIUMF have discovered something that they think may severely hinder the creation of room-temperature (37 degrees Celsius) superconductors.

Recommended for you

CERN: World-record current in a superconductor

22 hours ago

In the framework of the High-Luminosity LHC project, experts from the CERN Superconductors team recently obtained a world-record current of 20 kA at 24 K in an electrical transmission line consisting of two ...

High power laser sources at exotic wavelengths

Apr 14, 2014

High power laser sources at exotic wavelengths may be a step closer as researchers in China report a fibre optic parametric oscillator with record breaking efficiency. The research team believe this could ...

Novel technique opens door to better solar cells

Apr 14, 2014

A team of scientists, led by Assistant Professor Andrivo Rusydi from the Department of Physics at the National University of Singapore's (NUS) Faculty of Science, has successfully developed a technique to ...

User comments : 29

Adjust slider to filter visible comments by rank

Display comments: newest first

El_Nose
3 / 5 (1) Aug 17, 2012
Cold fusion - blah - look at the money spent looking for a high temp superconductor with almost nothing to show for it.

However if they find it, and which ever country finds it first will dominate the world for 30 years
Tausch
1 / 5 (2) Aug 17, 2012
'Ptolemy' substitutes for electron mechanics - until we get it right. No doubt some lucky reseacher(s) will have that long overdue flash of insight.
Satene
1 / 5 (5) Aug 17, 2012
The HT superconductors aren't so important economically. If we would have the reliable cold fusion source in every house, we wouldn't need any grid lines and superconductors with exception of few specialized short distance applications. Anyway, the main progress in research of HT superconductivity is currently done outside of mainstream and mainstream physicists tend to ignore it in similar way, like the cold fusion research. I discussed the reasons and aspects of this similarity here already many times...
Satene
1 / 5 (4) Aug 17, 2012
The simplest explanation of superconductivity is solely geometrical - no quantum effects are involved, just repulsive Coulomb force acting at distance.

Try to imagine the lone electron passing through sparse street made of another repulsive electrons (and/or attractive atom nuclei - it doesn't matter here). Because the distance from electron in motion and stationary particles changes periodically, the electron in motion will be subject of braking and accelerating forces, which will alternate periodically. Such an electron will accelerate and decelerate periodically and it will lose an energy with EM radiation during this.

But try to imagine, not only single electron, but the electron pairs or whole compact lines of electron would pass through the same street like the wagons in the train. In this case the line of electrons would behave like homogeneously charged rod and no periodic forces will affect its motion. The compactification / squeezing of electrons is the whole mystery here.
Satene
1 / 5 (4) Aug 17, 2012
The superconductivity competes with the charge density waves
How we should interpret this sentence in the light of the above explanation? Well, if the line of electrons isn't compacted enough, then the electrons may still move along it in periodical fashion like the loosely coupled wagons in the train. And they will radiate the energy in EM waves, which is the reason of Ohmic losses and the killer of superconductivity. Now you can understand the article subject without logical gaps (holes) and redundant concepts (bumps) involved. Your understanding may remain compact and as such smoothly superfluous.
Tausch
1 / 5 (2) Aug 17, 2012
Simply predict the combination of elements that has 'room temperature' superconductivity that underscores your version of the 'simplest explanation'.

All your comments to encourage and tax my imagination fall short.
ValeriaT
1 / 5 (5) Aug 17, 2012
We know about room temperature superconductors already 1. Only diamond has a lattice strong enough to withstand the pressure of electrons squeezed. The classical cuprate superconductors allow room temperature superconductivity too, but their current load is still very low 2.
Macksb
1 / 5 (2) Aug 17, 2012
This report is precisely consistent with many posts I have made over the last several years regarding coupled oscillators, or synchronized oscillators, and their relevance to superconductivity.

BCS theory involves coupled oscillators: phonons are vibrations or oscillations, and Cooper pairs are themselves coupled oscillations--spin and orbit are oscillations.

High temp superconductors may involve other synchronized or coupled oscillations. The synchronies themselves might be in different forms--perhaps more complex.

Huygens, Art Winfree, Kuramoto, Strogatz and others have all made contributions to the theory of coupled oscillators.

"One vibration of the copper oxide group changed its frequency" at the critical temp. "One vibration in the manganese oxide group reacted in the same way...in the whole LCMO layer." "We didn't expect the superconductivity would affect the vibration of the M-O." "Long-range electron phonon coupling." Synchronized oscillations at work, as predicted. HTS.
Minich
1 / 5 (2) Aug 19, 2012
1. BCS theory is the bullshit. Especially with electron pairing.
2. For any superconductor (cuprate, pnictide, conventional) theory of superconductivity is ONE ELECTRON theory.
3. Superconductivity and pseudogap effect are of order paremeter of the same nature (for solids without phonon superradiance).
3. This order parameter creates CDW. No inverse order, that CDW creates superconductivity.
4. In superconducting state superconducting electrons smooth CDW, that arise due to pseudogap state.
Minich
1 / 5 (2) Aug 19, 2012
5. For superconducting solids with phonon superradiance there is no pseudogap state. Such solids we name as conventional.
Macksb
1 / 5 (2) Aug 19, 2012
In one respect only I agree with Minich. I believe there will be one theory to explain all superconductors--cuprate, pnictide, conventional. Occam's Razor.

As I have said many times in the past, I believe that theory will be based on Art Winfree's theory of coupled oscillators, which he developed and applied in biomathematics, not physics, circa 1967. Systems of oscillators have a tendency to coordinate the frequency or frequencies of their oscillations, and when they do, they do so in certain extremely precise patterns, and no other patterns, as identified by Winfree. Think of his "law" as an algorithm for quantum patterns in which oscillators self-organize themselves and their frequencies.

That's why the above article is so interesting to me. "One vibration of the copper-oxide layer changed its frequency," exactly at the superconducting transition. That change in frequency indicates--to me--that the oscillations found a new and more profound form of organization.
ValeriaT
1 / 5 (2) Aug 19, 2012
BCS theory is the bullshit. Especially with electron pairing
It's not BS, for low temperatures it's well reasoned mechanism. Simulation runs at MS IE browser only.
Minich
1 / 5 (2) Aug 19, 2012
To Macksb
Coupled oscillator can show interesting effects anologous to superfluidity. The energy-momentum curve for zero "phonon" modes has all features for "superfluidity" of "zero" motion modes. It depends on nonlinearity of above mentioned curve.
Minich
1 / 5 (2) Aug 19, 2012
BCS theory is the bullshit. Especially with electron pairing
It's not BS, for low temperatures it's http://www.aether...ity.htm. Simulation runs at MS IE browser only.
BCS theory does bullshit. It was clear for me in 1980. I looked for a job in physics in 1977 and found the vacancy in the laboratory of SOLID helium in The Institute of Solid State Physics of USSR http://issp3.issp.ac.ru/engl/ There was a talk with a boss Mezhov-Deglin and i realized that there is no theories for superfluid helium-4 and superconducting electrons. It took me about 3 years to solve the mistery. Than i worked in defence industry and it was impossible for me to publish any paper. My work was classified and i think it is classified even now. I made simulation programm in Maple 16 (NAG oriented) for 1D and 2D cases. It will be published on my personal site in seprember 2012.
http://love.minich.ru/
ValeriaT
1 / 5 (2) Aug 19, 2012
You can publish what you want where you want, but here you should use a matter of facts arguments only. What is clear for you or not is not testable argument.
Macksb
1 / 5 (2) Aug 19, 2012
To Minich:

Thanks for your comment in response to mine. Once again we agree on a particular point...in this instance, that superfluidity exhibits behaviors analagous to systems of coupled oscillators. I go further...I have said in other posts that the two forms of superfluidity are additional instances in which Art Winfree's "law" of coupled oscillators is the fundamental explanation.

Winfree's law has been well tested over the last 45 years in mathematics, and Mother Nature embraces it fully in biology. In due course, physicists will discover it, with spectacular results. Winfree's law has ample potential to explain many forms of exotic emergent behavior. Another example: the fractional quantum Hall effect. But it also sheds light on more mundane behavior, such as solid-liquid-gas-plasma, and their transitions.
Planck's quantum is the very essence of a periodic oscillation--the only ingredient in Winfree's law.

Minich
1 / 5 (2) Aug 19, 2012
You can publish what you want where you want, but here you should use a matter of facts arguments only. What is clear for you or not is not testable argument.
:)
Why should i think about You? Or about anybody else?

Remember Kopernikus. He wrote the book and died before clericals cut his head off.
:)
Minich
1 / 5 (2) Aug 19, 2012
To Macksb
My personal opinion: I don' think Winfree's law is more general than superfluid instability. Oscillators are so rare in nature. For example electrons in solids are not oscillators.
Macksb
1 / 5 (2) Aug 19, 2012
To Minich:

Thanks for this conversation. Regarding superfluid instability, consider the vortices that emerge when superfluids are rotated past their breaking point. Those vortices are synchronized periodic oscillations. So is stable superfluidity, in which the helium atoms are synchronized by their own oscillations--coupled so strongly that they must stay joined, until new energy, above some point, breaks some bonds.

As to electrons, in my opinion they are a bundle of oscillations. Orbit and spin are periodic oscillations. The wobble within the spin is a periodic oscillation. And each one is related to Planck's quantum, which is a periodic oscillation that is the very foundation of physics and all of its components. As this implies, I have a broader definition of periodic oscillations (Winfree used the term "limit cycle oscillations") than most physicists. But I believe my definition is consistent with Winfree's concept, his terminology, and his mathematical expression.
Minich
1 / 5 (2) Aug 19, 2012
To Macksb

The point is in dispersion relations of quantum mechanical matter waves. If You could define waves in effect You could find something "superfluid" for such waves in superfluid "cases".

For example negative effective mass of electrons near fermi surface for conventional and most of cuprate hole superconductors (so called Chapnik Kikoin rule).
El_Nose
not rated yet Aug 20, 2012
high temp SC is more about better electronics at this point - more than energy transmission. While transmission is very important unless you are talking about high Speed rail - it's not a growth engine.

The big one is the future of electronics with processors that do not produce heat. Remember a Superconductor is energy transmission without resistance -- or without creating excess heat -- now try to imagine waht you could do to processing with a chip that never gets hot. you could scale it vertically and never need to cool it.
Minich
1 / 5 (2) Aug 20, 2012
1. If You have alternating current there be the HEAT.
2. Programms in practice ever have memory leakage, and we forever be have heat leakage in superconducting computers
3. Room temperature superconductors are the best for space weapons and aero weapons and especially for submarines with nuclear rocket weapons.
Minich
2.3 / 5 (3) Aug 20, 2012
For example the advantage of superconducting wind turbine is its weight: 50-55 tonns for 10mwt. Ordinary turbine with 10mwt weights 550 tonns.
Minich
1 / 5 (2) Aug 21, 2012
I doubt so, because the weight of turbine is determined with size of its paddles and its generator works with 98% efficiency already. Are you saying, the remaining 2% would eliminate 90% of turbine weight?
Of course You can doubt. But i've got the data from those people who had MADE already such wind turbines. You can ask somebody practical enginear, not theoretician.

Omega rpm for wind turbine is very low and inefficient for ordinary electrical generator.
Minich
1 / 5 (2) Aug 21, 2012
Mechanical reduction systems (train?) can be broken very frequently and must be heavy weighted to be non broked. Superconductivity is better in this case.
Minich
1 / 5 (2) Aug 21, 2012
Superconducting generator can work good even with low rotations per minite
El_Nose
not rated yet Aug 21, 2012
@Minich

all electronics are DC -- AC is how we transmit power -- but we use it in DC form. AC in a circuit diagram is hell on earth to solve continuously. Look it up -- have no fear my super cool computer is viable. Take a few electrical engineering courses
Minich
1 / 5 (2) Aug 21, 2012
@Minich

all electronics are DC -- AC is how we transmit power -- but we use it in DC form. AC in a circuit diagram is hell on earth to solve continuously. Look it up -- have no fear my super cool computer is viable. Take a few electrical engineering courses

Take some courses in school physics.

Information in computers is changed (processed). It is not ROM only. And even in read only memory it must be READ by electrical SIGNAL with CHANGES in electrical current.

So You can go in some direction with your notorious DC current!
Minich
1 / 5 (1) Aug 22, 2012
@Minich

all electronics are DC -- AC is how we transmit power -- but we use it in DC form. AC in a circuit diagram is hell on earth to solve continuously. Look it up -- have no fear my super cool computer is viable. Take a few electrical engineering courses

See :)
doi:10.1016/j.physc.2010.07.005
"Its (*superconducting) very low power dissipation of only 0.1 (microWatt) per gate at 100 GHz"

Where do you see zero heat?
http://www.ewh.ie...HP38.pdf

More news stories

CERN: World-record current in a superconductor

In the framework of the High-Luminosity LHC project, experts from the CERN Superconductors team recently obtained a world-record current of 20 kA at 24 K in an electrical transmission line consisting of two ...

Glasses strong as steel: A fast way to find the best

Scientists at Yale University have devised a dramatically faster way of identifying and characterizing complex alloys known as bulk metallic glasses (BMGs), a versatile type of pliable glass that's stronger than steel.

Making 'bucky-balls' in spin-out's sights

(Phys.org) —A new Oxford spin-out firm is targeting the difficult challenge of manufacturing fullerenes, known as 'bucky-balls' because of their spherical shape, a type of carbon nanomaterial which, like ...