Pinning Down Superconductivity to a Single Layer

Oct 29, 2009
In 2008, Bozovic's team reported discovery of interface high-temperature superconductivity in bilayer films of two cuprate materials, one a metal (M) and the other an insulator (I). Now they show that zinc doping dampens superconductivity (see drop in transition temperature indicated by blue line) only when placed in the second cuprate layer (highlighted) above the interface. Hence, this particular layer, less then 0.7 nanometers thick, is solely responsible for the materials high-temperature superconductivity. The result opens prospects for tunable superconducting electronic devices.

(PhysOrg.com) -- Using precision techniques for making superconducting thin films layer-by-layer, physicists at the U.S. Department of Energy's Brookhaven National Laboratory have identified a single layer responsible for one such material's ability to become superconducting, i.e., carry electrical current with no energy loss. The technique, described in the October 30, 2009, issue of Science, could be used to engineer ultrathin films with "tunable" superconductivity for higher-efficiency electronic devices.

"We wanted to answer a fundamental question about such films," said Brookhaven physicist and the group leader Ivan Bozovic. "Namely: How thin can the film be and still retain high-temperature ?"

The thinner the material (and the higher its to a superconductor), the greater its potential for applications where the can be controlled by an external electric field. "This type of control is difficult to achieve with thicker films, because an electric field does not penetrate into metals more than a nanometer or so," Bozovic explained.

To explore the limits of thinness, Bozovic's group synthesized a series of films based on the high-temperature superconducting cuprates (copper-oxides) — materials that carry current with no energy loss when cooled below a certain transition temperature (Tc). Since zinc is known to suppress the superconductivity in these materials, the scientists systematically substituted a small amount of zinc into each of the copper-oxide layers. Any layer where the zinc's presence had a suppressing effect would be clearly identified as essential to superconductivity in the film.

"Our measurements showed that the zinc doping had essentially no effect, except when placed in a single, well-defined layer. When the zinc was in that layer, the superconductivity was dramatically suppressed," Bozovic said.

The material studied by Bozovic's team was unusual in that it consists of layers of two materials, one metallic and one insulating, that are not on their own, but rather exhibit superconductivity at the interface between them [see Scientists create superconducting thin films].

The layer identified as essential to the superconductivity by the zinc-substitution experiment represents the second copper-oxide layer away from the interface. The scientists found that the presence of zinc had no effect on the transition temperature at which superconductivity sets in, about 32 kelvin (-241 Celsius), except when placed in that particular layer. In the latter case, the scientists observed a dramatic drop in the transition temperature to 18 kelvin (-255 Celsius). The reduction in transition temperature provides a clear indication that that particular layer is the "hot" one responsible for the relatively high temperature at which superconductivity normally sets in for this material.

"We now have a clean experimental proof that high-temperature superconductivity can exist, undiminished, in a single copper-oxide layer," Bozovic said. "This piece of information gives important input to our theoretical understanding of this phenomenon."

Bozovic explained that, in the material he studied, the electrons required for superconductivity actually come from the metallic material below the interface. They leak into the insulating material above the interface and achieve the critical level in that second copper-oxide layer.

But in principle, he says, there are other ways to achieve the same concentration of electrons in that single layer, for example, by doping achieved by applying electric fields. That would result in in a single copper-oxide layer measuring just 0.66 .

From a practical viewpoint, this discovery opens a path toward the fabrication of electronic devices with modulated, or tunable, superconducting properties which can be controlled by electric or magnetic fields.

"Electronic devices already consume a large fraction of our electricity usage — and this is growing fast." Bozovic continued. "Clearly, we will need less-power hungry electronics in the future." Superconductors, which operate without — particularly those that operate at warmer, more-practical temperatures — may be one way to go.

Bozovic's layer-by-layer synthesis method and ability to strategically alter individual layers' composition might also be used to explore and possibly control other electronic phenomena and properties that emerge at the interfaces between layered materials.

Source: Brookhaven National Laboratory (news : web)

Explore further: Puzzling new behaviour observed in high-temperature superconductors

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User comments : 27

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amansourf
Oct 29, 2009
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johanfprins
1 / 5 (4) Oct 30, 2009
It is so obvious what the mechanism is: I have already published the mechanism 7 years ago; but nobody is interested because it is NOT based on Cooper Pairs. At present I am able to manufacture thin-layer superconductors which operate at room and higher temperatures. If any company is willing to listen with an open mind, I can demonstrate prototypes.
henryjfry
Oct 30, 2009
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Alexa
3 / 5 (4) Oct 30, 2009
Your problem is problem of whole civilization with scientific establishment. Can you record some video of your experiments? You could share it on YouTube together with your comments, etc.
johanfprins
1 / 5 (2) Oct 31, 2009
Your problem is problem of whole civilization with scientific establishment. Can you record some video of your experiments? You could share it on YouTube together with your comments, etc.

What must I record? Making resisistivity and magnetic measurements? What I need now is a company with the required infrastructure to take my prototype superconducting layers and manufacture processor chips. We could have had this already five years ago.
Obviously I will supply prototypes, free of charge, so that such a company can first convince itself that superconduction is occurring at room temperature.
After 10 years of throwing pearls before physics-swine, I am writing a book called "The Physics Delusion" for people who still have common sense, in which I am unmasking the buffoons who have led physics over the last 100 years into Alice's Wonderland. Do you realise that our top physicists do not even understand when Ohm's law applies and when not?
Alexa
Nov 02, 2009
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Alexa
2.3 / 5 (3) Nov 02, 2009
Prof. Johan Prins has revealed in experiments with oxygen doped diamond layers, electrons can be attracted to diamond surface by oxygen atoms trapped beneath this surface, thus forming dense cloud there - so that superconductivity can occur even outside of atom lattice in free air! Such finding would even enable us to produce superconductive layers of free electrons by charge gradients onto surface of whatever sufficiently solid insulator, so we could control it from outside by this charge gradient like switch.

Unfortunately, most of scientists didn't recognize practical importance of this finding at all, particularly because prof. Prins's fight against BCS theory of superconductivity rendered him a crackpot in their eyes. In my opinion, we are losing huge amount of money by ignoring of this research.
Alexa
1 / 5 (2) Nov 02, 2009
.. I am writing a book called "The Physics Delusion" ..
Your negative experience will be useful for other generations from historical reasons - but I'd recommend You to hold a positively biased approach by now. You can create a YouTube video with 3D animations of the effect, you've revealed and to illustrate applications, in which it could be used to attract interest of publicity.

Let scientists to do their job and to waste time with their theories - you've some practical results already!
Alexa
Nov 02, 2009
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johanfprins
Nov 03, 2009
This comment has been removed by a moderator.
Alizee
Nov 03, 2009
This comment has been removed by a moderator.
johanfprins
Nov 04, 2009
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Alexa
not rated yet Nov 05, 2009
This is well known even from physorg articles, like these two:

http://www.physor...499.html
http://www.physor...850.html

But BCS theory isn't completely out of the game -just compare the Colin Humphreys theory and the appearance of real hole stripes.

These stripes are doubled - which means, they're formed by Cooper pairs, just arranged into groups, instead of single quasiparticles. Holes are magnetically paired and superconductivity hole-pairs march collectively along the channels, like trams on pairs of tramlines running between the blocks of houses. There is one hole on each tramline, according to this model, and the pairs of holes move down the channels, hopping from oxygen to oxygen via adjacent copper sites. The image of real hole stripes illustrates this situation clearly.

http://tinyurl.com/yf3luht
johanfprins
1 / 5 (1) Nov 05, 2009
I disagree:
This model also does not explain the defining characteristic of a superconductor: Namely how an electric-field is cancelled within a superconductor while a current is flowing: This is what Onnes measured originally.
If one cannot model the latter characteristic, the charge on the charge-carriers, whether they are bosons or not, becomes irrelevant since, such a charge carrier will be accelerated. When charge-carriers are accelerated they conduct NORMALLY, whether they scatter or not. The London bros. were unable to understand this simple aspect: Also all the luminaries BCS and Colin Humphries who followed in their footsteps.
Alexa
not rated yet Nov 05, 2009
BCS theory predicts the dependence of the value of the energy gap E and critical magnetic field on the critical temperature Tc, specific heat of the superconductor, Meissner effect, isotope effect, etc. up to temperatures 12 - 17 K. At higher temperatures it's followed by clustering of electrons, i.e. of pairs of individual electrons are replaced by pairs of spin oriented clusters - but central idea of BCS remains valid up to its classical limit. After all, existence Cooper pairs has been proven by Josephson tunneling and by evidence of broken pairs by photoemission spectroscopy, etc.
jgelt
not rated yet Nov 05, 2009
Is a conductive monolayer completely dissimilar from the 'skin effect'?
johanfprins
1 / 5 (1) Nov 06, 2009
After all, existence Cooper pairs has been proven by Josephson tunneling and by evidence of broken pairs by photoemission spectroscopy, etc.

It IS NOT proved by Josephson tunnelling. One has a charge-carrier on one side of the insulating layer which has to move through the layer and end up at the same energy on the other side if there is no voltage V over the layer. When there is a voltage, the energy on the other side is reduced by e times V: eV. When the charge-carrier with charge q moves through the layer it gains energy qV. It thus has an excess of energy (q+e)V which it must radiate way. Gues what does one measure? That (q+e) is equal to 2e: Thus q=e. If the charge-carriers were doubly charged one should have measured 3eV for Josephosn tunnelling: QED

It is easy to show that the results from photo-emission spectroscopy are incorrectly modelled. So is the results for flux quantization. When using correct physics one also find in this case that q=e.
johanfprins
1 / 5 (1) Nov 06, 2009
BCS theory predicts the dependence of the value of the energy gap E and critical magnetic field on the critical temperature Tc, specific heat of the superconductor, Meissner effect, isotope effect, etc. up to temperatures 12 - 17 K.

My model models all these effects in metals, CuO ceramics, highly doped p-type diamond, AND disordered superconducting layers. In all cases the same mechanism is active which defines a simple quadratic equation.
It also explains why an applied electric-field is cancelled while a current is flowing: This cannot be explained by BCS.
Consider ths following:
All elephants are mammals (correct): All mammals are elephants (not correct). To have superconduction one must have zero resistivity (correct): When having zero resistivity you have superconduction (not correct). Even my two year old grandson can understand this: Why can the "experts" on superconduction not?
johanfprins
1 / 5 (1) Nov 06, 2009
Is a conductive monolayer completely dissimilar from the 'skin effect'?

A SUPERconducting monolayer is totally different from the skin effect. In the CuO ceramics the materials consist entirely of superconducting monolayers; each forming between two crystollagraphic planes.
Alexa
5 / 5 (1) Nov 09, 2009
..my model models all these effects in metals..
Where we can read about your model in brief conscious form (link)?
..This cannot be explained by BCS...
I really doubt so...;-) You probably didn't understood this theory at all.
johanfprins
1 / 5 (1) Nov 09, 2009
[Where we can read about your model in brief conscious form (link)?

It is in my book entitled: "Superconduction at Room Temperature without Cooper Pairs". There are summaries on my website: http://www.cathodixx.com
I am now writing a new book entitled "The physics delusion" aimed at people who still have common sense: The latter is not found within the physics community anymore: It probably became extinct after Einstein and Schroedinger died.
This book will be announced within a week on my website and will be published next year.
It contains a section which summarises my model and applies to all superconductors.
I really doubt so...;-) You probably didn't understood this theory at all.
Let us see whther YOU understand it: Just answer the following question: Does an applied electric field accelerate Cooper pairs; and if not why not?
Alexa
not rated yet Nov 11, 2009
Does an applied electric field accelerate Cooper pairs; and if not why not?
It does - but it's not, what the superconductivity is about.
johanfprins
1 / 5 (1) Nov 11, 2009
Any conducting material in which the charge carriers are accelerated by an electric field is a normal conductor even when it has zero resistivity. Acceleration, whether there is scatterring or not will ALWAYS cause a voltage over two contacts WHILE A CURRENT IS FLOWING.
If not, then Newton's second law must be wrong which is unlikely.
THE DEFINING CHARACTERISTIC OF A SUPERCONDUCTOR IS THAT THE VOLTAGE OVER TWO CONTACTS BECOMES EXACTLY ZERO.
REALLY: This is primary school physics!
Alexa
not rated yet Nov 11, 2009
If you need a current, you're expected to have charge carriers in motion, so you need to accelerate them from their rest state.
Alexa
not rated yet Nov 11, 2009
The principle of Cooper pairs can be expressed by this picture of mine - I'm using it during explanations of BCS theory for kids... I mean kindergarten physics...

http://www.aether...zari.jpg
johanfprins
1 / 5 (1) Nov 12, 2009
If you need a current, you're expected to have charge carriers in motion, so you need to accelerate them from their rest state.

This is the crux of the matter which the "superconductor physics sect" has been missing for nearly 100 years:
If you accelerate ANYTHING using a conservative force, you change its potential energy: If not, Newton's laws must be wrong!
Thus if you apply a conservative electric field and accelerate Cooper pairs, you will measure a voltage along the direction in which they move: The experimental fact is that in a superconductor one cannot measure such voltage:
According to you the Cooper pairs accelerate. This means that Newton's laws become obsolete when Cooper pairs are involved: Is that what you are telling children in kindergarten?
The crux of the matter is that to model superconduction one must explain how the charge-carriers gain kinetic energy WITHOUT BEING ACCELERATED.
johanfprins
1 / 5 (1) Nov 12, 2009
The principle of Cooper pairs can be expressed by this picture of mine - I'm using it during explanations of BCS theory for kids... I mean kindergarten physics.

The picture is meaningless: In which direction is the couple moving? Please stop visiting Alice in Wonderland!
Alexa
Nov 13, 2009
This comment has been removed by a moderator.
Alexa
not rated yet Nov 13, 2009
As you can see, Cooper pair theory removes acelleration of electron pairs during their motion by assumption of their quantum entanglement into single particle, larger then the lattice constant. Of course, such principle can be extended easily to high temperature superconductivity, because the energy required for breaking of entangled pairs increases with increasing number of particles in both spin-entangled groups.
johanfprins
1 / 5 (1) Nov 13, 2009
It doesn't matter - when one member of Cooper pair increases its potential energy, another member is losing it and vice-versa. There is DHTML simulation of the same phenomena (works in MSIE only)...

Clever: But this is of course voodoo physics: To move the two partners, work has to be done by the applied electric-field on each one of them; or else they stay in equilibrium over the hump. Although in one case the work increases the potential energy and in the other case decreases the postential energy, both partners also gain kinetic-energy during the acceleration. You are ignoring the latter energy. I would have failed you if you were in my class at university.

johanfprins
1 / 5 (1) Nov 13, 2009
As you can see, Cooper pair theory removes acelleration of electron pairs during their motion by assumption of their quantum entanglement into single particle, larger then the lattice constant.

Further voodoo: Independent of the size of an entangled entity, if it has charge and is free to move, an applied conservative electric-field will accelerate it and increase its kinetic-energy. The only time you cannot accelerate a charged entity is when it is not free to be accelerated. Cooper pairs are free to be accelerated and will thus gain kinetic-energy whatever their internal interactions.
Please stop violating Newton's laws!
Alexa
not rated yet Nov 13, 2009
It's not my intention to evangelize BCS theory here. Cooper pairs indeed have kinetic energy, which is OK - this energy is stored in their magnetic field. But this is not what the superconductivity is about, because the very same effect applies to free electrons, too.
johanfprins
1 / 5 (1) Nov 13, 2009
Cooper pairs indeed have kinetic energy, OK - this energy is stored in their magnetic field.

Dear Alexa,
It is clear that you are not a fool. So why do you use arguments which violate the most elementary laws of physics?. Just because an army of idiots have repeated this claptrap for more than 50 years?
Any theory must explain experiment: What is Onnes' experimental result: As soon as superconduction sets in, the applied conservative electric-field is cancelled. No magnetic field can do this by "storing" this energy as magnetic energy. There is only one known way in which an electric field is cancelled and that is by an opposite polarisation field. And if ANY model cannot explain where this polarisation-field comes from it cannot model supercondduction. No model to date including BCS can do this. My model does!!!
johanfprins
Nov 18, 2009
This comment has been removed by a moderator.
johanfprins
Nov 18, 2009
This comment has been removed by a moderator.
johanfprins
Nov 20, 2009
This comment has been removed by a moderator.
johanfprins
1 / 5 (1) Nov 21, 2009
Are electrons still pairing by throwing sound around? Ha! Ha!
johanfprins
1 / 5 (1) Nov 22, 2009
Cooper pairing must sound like two cats: A lot of noise being exchanged all the time!