Superconductivity can be turned on and off with a powerful terahertz pulse

[William Gaatjes]

This is good research, the super conductive state could be disrupted with a short EM pulse.

http://www.physorg.com/news/2011-07-ultrafast-superconductors.html

The superconducting transport between the layers of a cuprate crystal (three layers, red and blue spheres represent the oxygen and copper atoms respectively) is controlled with an ultrashort terahertz pulse (yellow in the background). The three-dimensional superconductivity can thus be switched on and off very quickly (orange spheres represent electrons). © J.M. Harms, Max Planck Research Group for Structural Dynamics

(PhysOrg.com) -- A high-temperature superconductor can now be switched on and off within a trillionth of a second – 100 years after the discovery of superconductivity and 25 years after the first high-temperature superconductor was. A team including physicists from the University of Oxford and the Max Planck Research Group for Structural Dynamics at the University of Hamburg has realised an ultrafast superconducting switch by using intense terahertz pulses. This experiment opens up the possibility to discover more about the still unsettled cause of this type of superconductivity, and also hints at possible applications for ultrafast electronics in the future.

Superconductivity is one of the most remarkable effects in physics. Every electrical conductor has a resistivity, but some materials lose their resistivity completely if they are cooled to below a characteristic temperature; the current then flows without any loss whatsoever. When the Dutch physicist Heike Kamerlingh Onnes discovered this effect in 1911 in mercury, he initially believed that his measuring instruments were faulty, before he became aware of the significance of his monumental discovery.

“Normal” conductors such as mercury or lead must be cooled down to temperatures near absolute zero at minus 273.16 degrees Celsius in order to become superconducting. It was therefore a sensation when, in 1986, Johannes Georg Bednorz and Karl Alexander Müller presented a ceramic material that already became superconducting at minus 248 degrees Celsius. Since then, these cold conductors have been a burning issue with both scientists working in basic research and users. The ultrafast switch, which has now been developed by the research group working with Andrea Cavalleri, head of the Max Planck Research Group for Structural Dynamics at the University of Hamburg, is a further astonishing discovery in this field.


The high-temperature superconductor used by the Hamburg scientists has been known for a long time. It is a crystal based on lanthanum cuprate (La2CuO4) to which a specific quantity of strontium has been added (La1,84Sr0,16CuO4). Its transition temperature is minus 233 degrees Celsius. Although it is not yet completely clear how the superconductivity arises here, essential elements are known: “The crystal is formed by copper-oxygen planes which lie on top of each other like the pages of a book,” explains Cavalleri. The electrons can only move within these planes; the current transport therefore only occurs in two dimensions.

If the material is cooled below 40 Kelvin, a link is suddenly created between these two planes. Physicists explain this using the wave model, according to which the electrons are pictured not as particles, but as waves. Below the transition temperature the electrons from neighbouring planes overlap, and this allows the electric charge carriers to change from one plane to the other. Current is suddenly transported in all three spatial dimensions: the superconducting state has been created.

A terahertz pulse briefly destroys the coupling of the electrons

Cavalleri and his colleagues then wanted to know whether this transport between the layers can be deliberately interrupted and switched on again. In theory this is possible if a very strong electric field is applied at right angles to the layers. However, applying such a field is impractical. “This causes the crystal to heat upand the superconductivity collapses,” explains Cavalleri. The solution was to send in an ultrashort pulse of light to manipulate the superconductor.

This so-called terahertz pulse is an electromagnetic wave, similar to light, but with a much longer wavelength. It has an electric field that briefly destroys the coupling of the electron waves between the planes when it penetrates into the crystal. This is only successful if the electric field strength of the pulse is very high, in the order of several ten thousand volts per centimetre. And it must be short enough that it does not heat up the crystal.

Only recently has it been possible to generate such extremely powerful, ultrashort terahertz pulses. This is the task of team member Matthias Hoffmann. In very simple terms, this is done by the interaction of an ultrashort laser pulse with a lithium niobate crystal. An effect which physicists call optical rectification then generates the desired terahertz radiation in the crystal.

The experiment, which Andreas Dienst designed and carried out in Oxford, succeeded as anticipated: for the short time of less than one picosecond (10-12 seconds) as the pulse interacts with the superconductor, the coupling between the planes, and thus the superconductivity, was interrupted before subsequently returning. The superconductor does not suffer in this process and can be switched as often as one likes.
“This is a very fascinating result, because we can also use this method to investigate how high-temperature superconductors work,” says Cavalleri. It is also possible that this effect additionally has real-world applications. Basically, the switchable high-temperature superconductor works in a very similar way to a conventional field-effect transistor. This is a semiconductor whose ability to pass a current can be controlled by applying an electric voltage. Analogous to this, is conceivable that the high-temperature superconductor could be used as an ultrafast, nanoelectronic transistor that is controlled by microwaves.

More information: A. Dienst, M. Hoffmann, D. Fausti, J. Petersen, S. Pyon, T. Takayama, H. Takagi, A. Cavalleri, Bi-directional ultrafast electric-field gating of interlayer charge transport in a cuprate superconductor, Nature Photonics, adv. Online public., 26. Juni 2011, DOI: 10.1038/NPHOTON.2011.124

 

[C1]

There is a need for hyper switches for use in quantum physics experiments.

 

[Ghiedo27]

[the pulse] must be short enough that it does not heat up the crystal.

as the pulse interacts with the superconductor, the coupling between the planes, and thus the superconductivity, was interrupted before subsequently returning. The superconductor does not suffer in this process and can be switched as often as one likes.

Is there any information on the practical rate of switching you can achieve with the pulse? The article appears to be contradictory. The pulse has to be short, but can somehow be used as often as you want?

 

[Sunny129]

The article appears to be contradictory. The pulse has to be short, but can somehow be used as often as you want?

that does indeed seem somewhat contradictory. first of all, even the weakest electromagnetic pulse imparted to the crystal for even the shortest length of measurable time is going to heat up the crystal. of course infinitesimally weak electromagnetic fields applied over infinitesimally short pulses is going to result in an infinitesimal increase in the crystal's temperature. so when the scientists say that the pulse must not increase the temperature of the crystal, what they really mean to say is that the electromagnetic pulse must not increase the temperature of the crystal enough to effect its property of superconductivity.

that being said, we know that each EM pulse used in the experiment increased the temperature of the crystal at least a little bit, just not enough to kill its ability to superconduct. whether this increase in temperature is large enough to be measurable or not, i don't know. now, if a 1-picosecond EM pulse is short enough to not change the crystal's temperature significantly enough to kill its superconductivity, that's just fine. but the crystal is going to need some time to shed that specific the excess heat from the EM pulse and get back to its starting temp. how long that takes i would imagine depends on the method of cooling, so theoretically it could take less time, the same amount of time, or more time than it did to heat the crystal. this implies a natural limit for the frequency of the pulses used in the experiment. in other words, if the EM pulses are applied to the crystal at a rate above this natural limit, the crystal will not be able to shed heat at a rate equal to or greater than the rate at which it acquired the heat in the first place. i.e. its temperature will continually increase until it eclipses its own critical temperature for superconductivity, and will cease to be a superconductor at that instant.

so, can a 1-picosecond EM pulse be applied quite often? i think so. but can it be applied as often as we'd like without eventually killing a material's superconductivity? logic tells us no. of course this is not a theory i stand firm by...after all, if there's one thing i've learned about such topics as relativity theory, quantum mechanics, and superconductivity, its that logic and intuition can be highly misleading...

 

[William Gaatjes]

With what i can understand of it, is that they use the electric component of the pulse which is an electromagnetic wave itself. But the repetition rate of firing pulses depends on how much heating occurs locally i would think. Superconductivity occurs here because the atoms rearrange themselves in the lattice depending on the temperature. Thus i would think that the temperature increase must be avoided.

As a side note I posted a link once on this forum section where researches found more indirect proof that the atoms in the lattice rearrange themselves just prior before superconductivity kicks in with these kind of materials (There are different groups of super conductors all with their own theory of the how and why about super conduction.) They applied high mechanical pressure on iron.

This is about iron based superconductors where the lattice changing shape as well.
http://www.sciencedaily.com/releases/2008/11/081113140422.htm

In two new papers on a recently discovered class of high-temperature superconductors, they report that the already complicated relationship between magnetism and superconductivity may be more involved than previously thought, or that a whole new mechanism may drive some types of superconductors.

At temperatures approaching absolute zero, many materials become superconductors, capable of carrying vast amounts of electrical current with no resistance. In such low-temperature superconductors, magnetism is a villain whose appearance shatters the fragile superconductive state. But in 1986, scientists discovered "high temperature" (HTc) superconductors capable of operating much warmer than the previous limit of 30 degrees above absolute zero.

In fact, today's copper-oxide materials are superconductive in liquid nitrogen, a bargain-priced coolant that goes up to a balmy 77 degrees above absolute zero. Such materials have enabled applications as diverse as high-speed maglev trains, magnetic-resonance imagers and highly sensitive astronomical detectors. Still, no one really understands how HTc superconductivity works, although scientists have long suspected that in this case, magnetism boosts rather than suppresses the effect.

The beginnings of what could be a breakthrough came in early 2008 when Japanese researchers announced discovery of a new class of iron-based HTc superconductors. In addition to being easier to shape into wires and otherwise commercialize than today's copper-oxides, such materials provide scientists fresh new subjects with which to develop and test theories about HTc superconductivity's origins.

Scientists at NIST's Center for Neutron Research and a team including researchers from the University of Tennessee at Knoxville, Oak Ridge National Laboratory, the University of Maryland, Ames Laboratory and Iowa State University used beams of neutrons to peek into a superconductor's atomic structure. They first found iron-based superconductors to be similar to copper-oxide materials in how "doping" (adding specific elements to insulators in or around a HTc superconductor) influences their magnetic properties and superconductivity.

Then the team tested the iron-based material without doping it. Under moderate pressure, the volume of the material's crystal structure compressed an unusually high 5 percent. Intriguingly, it also became superconductive without a hint of magnetism.

The iron-based material's behavior under pressure may suggest the remarkable possibility of an entirely different mechanism behind superconductivity than with copper oxide materials, NIST Fellow Jeffrey Lynn said. Or it could be that magnetism is simply an ancillary part of HTc superconductivity in general, he said—and that a similar, deeper mechanism underlies the superconductivity in both. Understanding the origin of the superconductivity will help engineers tailor materials to specific applications, guide materials scientists in the search for new materials with improved properties and, scientists hope, usher in higher-temperature superconductors.

There is also research done (on another material) where a certain amount of mechanical pressure caused the super conductive state. But when the pressure was increased, the super conductive state would disappear until the pressure reached another sweet spot and the super conductive state happened again. This seems to suggest that the rearrangement of the atoms is the key for super conduction for these group of (high temperature)super conductors..

This thread is about super conduction :
http://forums.anandtech.com/showthread.php?t=2082665&highlight=super+conduction+lattice
There is even a researcher (Johan F Prins) posting about his research and super conduction. I must look around to see if there is any news about his research.

 

[William Gaatjes]

Found it :

http://www.sciencedaily.com/releases/2010/01/100125172954.htm

They have speculated that under certain pressure and temperature conditions hydrogen could be squeezed into a metal and possibly even a superconductor, but proving it experimentally has been difficult. High-pressure researchers, including Carnegie's Ho-kwang (Dave) Mao, have now modeled three hydrogen-dense metal alloys and found there are pressure and temperature trends associated with the superconducting state -- a huge boost in the understanding of how this abundant material could be harnessed.

The study is published in the January 25, 2010, early, on-line edition of the Proceedings of the National Academy of Sciences.

All known materials have to be cooled below a very low, so-called, transition temperature to become superconducting, making them impractical for widespread application. Scientists have found that in addition to chemical manipulation to raise the transition temperature, superconductivity can also be induced by high pressure. Theoretical modeling is very helpful in defining the characteristics and pressures that can lead to high transition temperatures. In this study, the scientists modeled basic properties from first principles -- the study of behavior at the atomic level -- of three metal hydrides under specific temperature, pressure, and composition scenarios. Metal hydrides are compounds in which metals bind to an abundance of hydrogen in a lattice structure. The compounds were scandium trihydride (ScH3), yttrium trihydride (YH3) and lanthanum trihydride (LaH3).

"We found that superconductivity set in at pressures between roughly 100,000 to 200,000 times atmospheric pressure at sea level (10 to 20 GPa), which is an order of magnitude lower than the pressures for related compounds that bind with four hydrogens instead of three," remarked Mao, of Carnegie's Geophysical Laboratory. Lanthanum trihydride stabilized at about 100,000 atmospheres and a transition temperature of -- 423°F (20 Kelvin), while the other two stabilized at about 200,000 atmospheres and temperatures of -427 °F (18 K) and -387 °F (40 K) for ScH3 and YH3 respectively.

The researchers also found that two of the compounds, LaH3 and YH3, had more similar distributions of vibrational energy to each other than to ScH3 at the superconducting threshold and that the transition temperature was highest at the point when a structural transformation occurred in all three. This result suggests that the superconducting state comes from the interaction of electrons with vibrational energy through the lattice. At pressures higher than 350,000 atmospheres (35 GPa) superconductivity disappeared and all three compounds became normal metals. In yttrium trihydride, the superconductivity state reappeared at about 500,000 atmospheres, but not in the others. The scientists attributed that effect to its different mass.

 

[Sunny129]

wow, how exactly do they produce pressures on the order of a gigaPascal in the laboratory?

 

[Ghiedo27]

/wild speculation

Could the different stable temperature + pressure points be related to the orbital that's conducting? I have this image in my head of the superconductor being dense enough to change which electron acts as the valance electron. Not really an educated guess, just a guess heh.

 

[William Gaatjes]

/wild speculation

Could the different stable temperature + pressure points be related to the orbital that's conducting? I have this image in my head of the superconductor being dense enough to change which electron acts as the valance electron. Not really an educated guess, just a guess heh.

IMHO:
I personally think it is the same as this picture when super conduction takes place.

I think it is that the electrons can not slide along because the waves of the individual atoms and their components do not add up harmonically in the normal resistive state. I do not know the right words to explain it properly, but when electrons can hop along where the different electric fields cause a smooth flow without jitter (the process called electron scattering that is causing resistance) it would be the super conducting state. It is similar as a surfer riding the wave. Where the wave is comprised of all the separate waves of the individual atoms. I always see the normal "resistive state" as a state where the electrons experience slow downs and speed ups releasing and absorbing em radiation in the process which get finally transmitted as thermal radiation. The surfer in the analogy experiences a very bumpy wave. It would be similar as a car with wooden wheels on a brick road.

 

[William Gaatjes]

wow, how exactly do they produce pressures on the order of a gigaPascal in the laboratory?

I know they use diamond anvils.
To reach the pressure i think it is similar as this :
1000 N force on a square of 1m by 1 m is not that heavy when comparing that same 1000 N on a square of 1 micrometer by 1 micrometer.

 

[Sunny129]

i see, so they're simply using the definition of pressure (force per unit area) to their advantage. i.e. they're producing very high pressures by applying very high forces to very small areas...that makes enough sense. i guess i was initially taken aback by the immense pressures seen in those experiments, and didn't stop to do any magnitude analysis...otherwise i might have realized that such pressures can't be that far fetched in the real world so long as one uses a large enough force and a small enough area of application.

 

[TecHNooB]

IMHO:
I personally think it is the same as this picture when super conduction takes place.

I think it is that the electrons can not slide along because the waves of the individual atoms and their components do not add up harmonically in the normal resistive state. I do not know the right words to explain it properly, but when electrons can hop along where the different electric fields cause a smooth flow without jitter (the process called electron scattering that is causing resistance) it would be the super conducting state. It is similar as a surfer riding the wave. Where the wave is comprised of all the separate waves of the individual atoms. I always see the normal "resistive state" as a state where the electrons experience slow downs and speed ups releasing and absorbing em radiation in the process which get finally transmitted as thermal radiation. The surfer in the analogy experiences a very bumpy wave. It would be similar as a car with wooden wheels on a brick road.

I don't know anything about superconductors, but they're supposed to have 0 voltage aka no E-field aka no charge acceleration.

 

[Sunny129]

I don't know anything about superconductors, but they're supposed to have 0 voltage aka no E-field aka no charge acceleration.

indeed...we need only look at Ohm's Law to see this - it tells us that E=IR (voltage = current x resistance). if there is zero resistance in a superconductor, it follows that voltage will also be zero regardless of current.

 

[Born2bwire]

I don't know anything about superconductors, but they're supposed to have 0 voltage aka no E-field aka no charge acceleration.

Classic superconductivity works because a pair of electrons can experience long distance coherence in what are known as Cooper pairs. The coherence arises because the electrons disturb the positive ionic lattice which causes an increase in the positive charge around the electron. This imbalance in the charge density attracts another electron further away and couples the two electrons. The Cooper pairs when taken together as a pseudostate are bosons which allows a large number of electrons to effectively occupy the same state (and being bosons they want to occupy the same state). This means that you do not have the scattering of electrons into different states that causes resistance. Finally, because you can get such a large number of Cooper pairs into identical states then the quantum behavior is highly correlated to the macroscopic behavior that is observed. But back to what you have stated, yes, there is no electric field inside a superconductor for basically the same reasons why we assume that there is no field inside a conductor in electrostatics. With the superconductor state though, there is now no resistance to the charges automatically adjusting themselves in cancelling out the electric fields that arise due to regional charge imbalances.

 

[William Gaatjes]

I don't know anything about superconductors, but they're supposed to have 0 voltage aka no E-field aka no charge acceleration.

IMHO, on average yes. I do think that even a static dc field is not in reality an environment where nothing changes. Just because we perceive or assume standing still, does not mean that it is actually the case. Relative 0 does not mean the same as absolute 0.

 

[William Gaatjes]

i see, so they're simply using the definition of pressure (force per unit area) to their advantage. i.e. they're producing very high pressures by applying very high forces to very small areas...that makes enough sense. i guess i was initially taken aback by the immense pressures seen in those experiments, and didn't stop to do any magnitude analysis...otherwise i might have realized that such pressures can't be that far fetched in the real world so long as one uses a large enough force and a small enough area of application.

I think it is just the same as the the terahertz pulse. It is relative. A little power in a long time. A lot of power in a short time. A little pressure in a large area, a lot of pressure in a small area.

Makes me think about mass and what was meant in the past about very heavy masses on very small scales and what effects it should have when thinking of gravitational pull. Gravity ripples getting very small indeed. What would happen if a gravity ripple would come into the range of the EM spectrum ?

 

[William Gaatjes]

Classic superconductivity works because a pair of electrons can experience long distance coherence in what are known as Cooper pairs. The coherence arises because the electrons disturb the positive ionic lattice which causes an increase in the positive charge around the electron. This imbalance in the charge density attracts another electron further away and couples the two electrons. The Cooper pairs when taken together as a pseudostate are bosons which allows a large number of electrons to effectively occupy the same state (and being bosons they want to occupy the same state). This means that you do not have the scattering of electrons into different states that causes resistance. Finally, because you can get such a large number of Cooper pairs into identical states then the quantum behavior is highly correlated to the macroscopic behavior that is observed. But back to what you have stated, yes, there is no electric field inside a superconductor for basically the same reasons why we assume that there is no field inside a conductor in electrostatics. With the superconductor state though, there is now no resistance to the charges automatically adjusting themselves in cancelling out the electric fields that arise due to regional charge imbalances.

Is the cooper pair theory not the BCS theory that only works near absolute 0K ? For example the famous example of super conducting lead researched and first discovered/ experienced by Gilles Holst and proposed by Kamerlingh Onnes is theorized to be a BCS super conductor. IIRC for "high" temperature super conductors, other mechanisms are responsible. What you mention is a theory proposed for type 1 super conductors.

 

[William Gaatjes]

New research again shows that super conductivity appears at specific pressures and then disappears again. Prior research with other materials showed the same effect.


http://www.physorg.com/news/2012-02-physicists-reappearing-superconductivity-iron-selenium.html

Physicists surprised by disappearing and reappearing superconductivity in iron selenium chalcogenides

Superconductivity is a rare physical state in which matter is able to conduct electricity -- maintain a flow of electrons -- without any resistance. This phenomenon can only be found in certain materials at low temperatures, or can be induced under chemical and high external pressure conditions. Research to create superconductors at higher temperatures has been ongoing for two decades with the promise of significant impact on electrical transmission. New work from a team including Carnegie's Xiao-Jia Chen and Ho-kwang "Dave" Mao demonstrates unexpected superconductivity in a type of compounds called iron selenium chalcogenides. Their work is published online by Nature on February 22.
The New Superconductor - Boron Nano Powder For MgB2. ISO 9001:2000. - www.SpecMaterials.com/Super
A superconducting substance's electrical resistance disappears at a critical transition temperature, TC. The early conventional superconductors had to be cooled to extremely low temperatures—below TC—in order for electricity to flow freely. Then in the 1980s, scientists discovered a class of relatively high-temperature superconductors. Researchers have continued to study this phenomenon and look for it in an array of materials. It has been established that superconductivity can be affected by a substance's crystallographic structure, electronic charge, or the orbit of its electrons.
Recently scientists have discovered superconductivity in iron-based selenium chalcogenides. Chalcogenides are compounds that combine an element from group 16 on the periodic table (referring sulfur, selenium, tellurium) with another element, in this case iron. A selenide is a chemical compound containing selenium.
It was known that under pressure iron selenides become superconducters between -406 and -402 degrees Fahrenheit (30-32 K). But the research team, led equally by Liling Sun of the Chinese Academy of Sciences and Xiao-Jia Chen, discovered a second wave of superconductivity can be observed at higher pressures.
Working on an iron-based selenide the team observed a transition temperature that started at -400 degrees Fahrenheit (33 K) under about 16,000 times normal atmospheric pressure (1.6 GPa) and shifts to lower temperatures as the pressure increases, until it vanishes at about 89,000 times atmospheric pressure (9 GPa). But then superconducting reappears at pressures with a transition temperature of about -373 degrees Fahrenheit at around 122,000 times atmospheric pressure (12.4 GPa).
"These observations highlight the search of high-temperature superconductivity in complex structural and magnetic materials," Chen said. They confirmed these results with a variety of magnetic and electrical resistance measurements. They were also able to find reemerging superconductivity in another type of iron-based selenium chalcogenide, under very similar conditions.
They observed that the basic structure of these compounds was not changed under the extreme pressure and thus further research is needed to determine what is happening on a closer structural level.
Chen stated that "our work will likely stimulate a great deal of future study, both experimental and theoretical, in order to clarify what causes this reemergence of superconductivity."

But this reasearch happened before :

Super conductive hydrogen.

http://www.sciencedaily.com/releases/2010/01/100125172954.htm

"We found that superconductivity set in at pressures between roughly 100,000 to 200,000 times atmospheric pressure at sea level (10 to 20 GPa), which is an order of magnitude lower than the pressures for related compounds that bind with four hydrogens instead of three," remarked Mao, of Carnegie's Geophysical Laboratory. Lanthanum trihydride stabilized at about 100,000 atmospheres and a transition temperature of -- 423°F (20 Kelvin), while the other two stabilized at about 200,000 atmospheres and temperatures of -427 °F (18 K) and -387 °F (40 K) for ScH3 and YH3 respectively.

The researchers also found that two of the compounds, LaH3 and YH3, had more similar distributions of vibrational energy to each other than to ScH3 at the superconducting threshold and that the transition temperature was highest at the point when a structural transformation occurred in all three. This result suggests that the superconducting state comes from the interaction of electrons with vibrational energy through the lattice. At pressures higher than 350,000 atmospheres (35 GPa) superconductivity disappeared and all three compounds became normal metals. In yttrium trihydride, the superconductivity state reappeared at about 500,000 atmospheres, but not in the others. The scientists attributed that effect to its different mass.

I find it interesting that the superconductive state appeared in between 10 GPa and 20 GPa. 35GPa the superconductive state disappeared and at 50GPa it appeared again.

I wonder why that is... I am curious if the pressure would be increased again if it would disappear again and again at higher pressures re appear.
Maybe it is like multiples of a frequency, overtones.

We have temperature : (lattice control)
We have pressure : (lattice control)

And it is reoccurring. When other research was done, it was found out that the lattice changes shape.

Iron-Based Materials May Unlock Superconductivity’s Secrets

ScienceDaily (Nov. 13, 2008) — Researchers at the National Institute of Standards and Technology (NIST) are decoding the mysterious mechanisms behind the high-temperature superconductors that industry hopes will find wide use in next-generation systems for storing, distributing and using electricity.
In two new papers on a recently discovered class of high-temperature superconductors, they report that the already complicated relationship between magnetism and superconductivity may be more involved than previously thought, or that a whole new mechanism may drive some types of superconductors.
At temperatures approaching absolute zero, many materials become superconductors, capable of carrying vast amounts of electrical current with no resistance. In such low-temperature superconductors, magnetism is a villain whose appearance shatters the fragile superconductive state. But in 1986, scientists discovered "high temperature" (HTc) superconductors capable of operating much warmer than the previous limit of 30 degrees above absolute zero.
In fact, today's copper-oxide materials are superconductive in liquid nitrogen, a bargain-priced coolant that goes up to a balmy 77 degrees above absolute zero. Such materials have enabled applications as diverse as high-speed maglev trains, magnetic-resonance imagers and highly sensitive astronomical detectors. Still, no one really understands how HTc superconductivity works, although scientists have long suspected that in this case, magnetism boosts rather than suppresses the effect.
The beginnings of what could be a breakthrough came in early 2008 when Japanese researchers announced discovery of a new class of iron-based HTc superconductors. In addition to being easier to shape into wires and otherwise commercialize than today's copper-oxides, such materials provide scientists fresh new subjects with which to develop and test theories about HTc superconductivity's origins.
Scientists at NIST's Center for Neutron Research and a team including researchers from the University of Tennessee at Knoxville, Oak Ridge National Laboratory, the University of Maryland, Ames Laboratory and Iowa State University used beams of neutrons to peek into a superconductor's atomic structure. They first found iron-based superconductors to be similar to copper-oxide materials in how "doping" (adding specific elements to insulators in or around a HTc superconductor) influences their magnetic properties and superconductivity.
Then the team tested the iron-based material without doping it. Under moderate pressure, the volume of the material's crystal structure compressed an unusually high 5 percent. Intriguingly, it also became superconductive without a hint of magnetism.
The iron-based material's behavior under pressure may suggest the remarkable possibility of an entirely different mechanism behind superconductivity than with copper oxide materials, NIST Fellow Jeffrey Lynn said. Or it could be that magnetism is simply an ancillary part of HTc superconductivity in general, he said—and that a similar, deeper mechanism underlies the superconductivity in both. Understanding the origin of the superconductivity will help engineers tailor materials to specific applications, guide materials scientists in the search for new materials with improved properties and, scientists hope, usher in higher-temperature superconductors.

This makes me think again of that copper conducts better then aluminum. Even while copper has more atoms, it has less free electrons when compared to aluminum. That makes me think of less interference.
We know about strained silicon. The lattice is rearranged and this allows for less interference for electrons. This allows for a better flow of electrons.

 

[William Gaatjes]

This makes me think again of that copper conducts better then aluminum. Even while copper has more atoms, it has less free electrons when compared to aluminum. That makes me think of less interference.
We know about strained silicon. The lattice is rearranged and this allows for less interference for electrons. This allows for a better flow of electrons.

I mentioned a flow of electrons in my post. This is the case until we start using AC. Because then the flow of "information" is really the passing on of EM energy from electron to electron.

And with this i have a question. How high can the frequency be that a superconducting transformer still operates ?

I mean, we have dissipative copper losses eliminated because the windings are made of super conducting material. But we also have eddy currents flowing in the core and we have hysteresis losses in the core. With a normal iron core these losses can become considerably at higher frequencies. That is why for example metal powder cores and ferrite cores exist for AC transformers that are used with high frequencies. Lower Eddy currents and lower hysteresis losses. End of this side note.

The interesting question : When we have a superconducting coil or a superconducting transformer, intuition tells me that there should be a frequency where there is no longer any super conduction at a given current level. Intuition tells me : The higher the frequency of the current, the lower the maximum current level will be... But maybe i am wrong.
The reason why i think this is the case, is that the electrons must pass on EM energy.
Electrons travel through a material at a speed of a few cm / second. Thus AC energy is passed on as EM energy from electron to electron. At least that is the consensus.

There should be a point where passing on EM energy becomes a disturbance.
Would this become some kind of Compton scattering with the difference that there is no resting electron ?

Or am i forgetting something ?

 

[William Gaatjes]

Eddy currents in the super conducting material. And the skin effect.

 

[Evadman]

Is it wierd that the only thing I took away from this thread is that we can generate 50 GPa on a sample? I didn't know we could go that high in pressure.

Yay us!

 

[Howard]

Is it wierd that the only thing I took away from this thread is that we can generate 50 GPa on a sample? I didn't know we could go that high in pressure.

Yay us!

http://en.wikipedia.org/wiki/Diamond_anvil_cell

 

[William Gaatjes]

This is certainly interesting. I wonder if it can only happen in a plasma ?
I doubt that...


http://www.physorg.com/news/2012-03-ions-closer-physical-quantum-plasmas.html

When ions get closer: New physical attraction between ions in quantum plasmas
Nowadays, ever smaller and more powerful computer chips are in demand. German physicists have discovered a new physical attraction that accelerates this progress.

Prof. Dr. Padma Kant Shukla and Dr. Bengt Eliasson found a previously unknown phenomenon in quantum plasmas. A negatively charged potential makes it possible to combine positively charged particles (ions) in atom-like structures within the plasma. In this way, current can be conducted much more quickly and efficiently than before, opening new perspectives for nanotechnology. The researchers report on their findings in Physical Review Letters.

An ordinary plasma is an ionized electrically conducting gas consisting of positive (ions) and negative charge carriers (so-called non-degenerate electrons). This is the chief constituent of our solar system. On Earth, such plasmas among others can be used to produce energy in controlled thermonuclear fusion plasmas similar to the sun, or even to fight disease in the medical application field.

Quantum plasmas extend the area of application to nano-scales, where quantum-mechanical effects gain significance. This is the case when, in comparison to normal plasmas, the plasma density is very high and the temperature is low. Then the newly discovered potential occurs, which is caused by collective interaction processes of degenerate electrons with the quantum plasma. Such plasmas can be found, for example, in cores of stars with a dwindling nuclear energy supply (white dwarfs), or they can be produced artificially in the laboratory by means of laser irradiation. The new negative potential causes an attractive force between the ions, which then form lattices. They are compressed and the distances between them shortened, so that current can flow through them much faster.

The findings of the Bochum scientists open up the possibility of ion-crystallization on the magnitude scale of an atom. They have thus established a new direction of research that is capable of linking various disciplines of physics. Applications include micro-chips for quantum computers, semiconductors, thin metal foils or even metallic nano-structures.

More information: P. K. Shukla and B. Eliasson (2012): Novel Attractive Force Between Ions in Quantum Plasmas, Physical Review Letters 108, in press.

Provided by Ruhr-University Bochum

 

[Lemon law]

Is it just me, but there is something a little defective in saying an strong EM pulse can disrupt superconductivity.

When the holy grail is achieving and keeping superconductivity, why is it an advance to temporarily disrupt the super conductive state?

 

[epidemis]

This makes me think again of that copper conducts better then aluminum. Even while copper has more atoms, it has less free electrons when compared to aluminum.

That's because an Ion lacking 3 charges is less stable than one lacking 1 or 2. I can imagine the attractive forces of aluminium is slightly higher than copper on the electrons.