Physicists discover new properties of superconductivity

February 4, 2016
A magnet levitating above a cuprate high temperature superconductor. New findings from an international collaboration led by Canadian scientists may eventually lead to a theory of how superconductivity initiates at the atomic level, a key step in understanding how to harness the potential of materials that could provide lossless energy storage, levitating trains and ultra-fast supercomputers. Credit: Robert Hill/University of Waterloo

New findings from an international collaboration led by Canadian scientists may eventually lead to a theory of how superconductivity initiates at the atomic level, a key step in understanding how to harness the potential of materials that could provide lossless energy storage, levitating trains and ultra-fast supercomputers.

Professor David Hawthorn, Professor Michel Gingras, doctoral student Andrew Achkar, and post-doctoral fellow Dr. Zhihao Hao from University of Waterloo's Department of Physics and Astronomy have experimentally shown that electron clouds in superconducting materials can snap into an aligned and directional order called nematicity.

"It has become apparent in the past few years that the electrons involved in superconductivity can form patterns, stripes or checkerboards, and exhibit different symmetries - aligning preferentially along one direction," said Professor Hawthorn. "These patterns and symmetries have important consequences for superconductivity - they can compete, coexist or possibly even enhance superconductivity. "

Their results, published today in the prestigious journal Science, present the most direct experimental evidence to date of electronic nematicity as a universal feature in cuprate .

"In this study, we identify some unexpected alignment of the electrons - a finding that is likely generic to the high temperature superconductors and in time may turn out be a key ingredient of the problem," said Professor Hawthorn.

Superconductivity, the ability of a material to conduct an electric current with zero resistance, is best described as an exotic state in high temperature superconductors - challenging to predict, let alone explain.

The scientists used a novel technique called soft x-ray scattering at the Canadian Light Source synchrotron in Saskatoon to probe electron scattering in specific layers in the cuprate crystalline structure. Specifically, the individual cuprate (CuO2) planes, where electronic nematicity takes place, versus the crystalline distortions in between the CuO2 planes.

Electronic nematicity happens when the electron orbitals align themselves like a series of rods - breaking their unidirectional symmetry apart from the symmetry of the crystalline structure.

The term "nematicity" commonly refers to when liquid crystals spontaneously align under an electric field in liquid crystal displays. In this case, it is the electronic orbitals that enter the nematic state as the temperature drops below a critical point.

Recent breakthroughs in high-temperature superconductivity have revealed a complex competition between the superconductive state and charge density wave order fluctuations. These periodic fluctuations in the distribution of the electrical charges create areas where electrons bunch up in high- versus low-density clouds, a phenomenon that is now recognized to be generic to the underdoped cuprates.

Results from this study show electronic nematicity also likely occurs in underdoped cuprates. Understanding the relation of nematicity to charge density wave order, and an individual material's crystalline structure could prove important to identifying the origins of the superconducting and so-called pseudogap phases.

The authors also found the choice of doping material impacts the transition to the nematic state. Dopants, such as strontium, lanthanum, and even europium added to the cuprate lattice, create distortions in the lattice structure which can either strengthen or weaken nematicity and charge density wave order in the CuO2 layer.

Although there is not yet an agreed upon explanation for why electronic nematicity occurs, it may ultimately present another knob to tune in the quest to achieve the ultimate goal of a room temperature superconductor.

"Future work will tackle how electronic nematicity can be tuned, possibly to advantage, by modifying the ," says Hawthorn.

Hawthorn and Gingras are both Fellows of the Canadian Institute For Advanced Research. Gingras holds the Canada Research Chair in Condensed Matter Theory and Statistical Mechanics and spent time at the Perimeter Institute of Theoretical Physics as a visiting researcher while this work was being carried out.

Explore further: Unraveling the complex, intertwined electron phases in a superconductor

More information: "Nematicity in stripe-ordered cuprates probed via resonant x-ray scattering" Science, DOI: 10.1126/science.aad1824

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Hyperfuzzy
1 / 5 (2) Feb 04, 2016
Can't see the forest for the trees. Under what conditions must an imaginary channel be to allow what ever field, at what ever power and frequency and have no loss of state? Pretty sure all directions and alignment with only delta E received as simply a static field within the frequency domain. The projection onto a superimposed image of this domain may be simulated with only "+" and "-" particle position and particle count. It's looks like a search for a magic number. But first the engine, then let the engine do the search. Can't be more than a few weeks with a super computer. There's only so many stable conditions that is stable under any magnetic or electrical fields. You guys are doing an Easter egg hunt. Current, who needs current, why not let Vb +delta L = Va, with delta t = L/c. No power loss, ..., get it, the field and the particles must meet these conditions in space and time, so just make a 4D space, and make t = Lambda, then the same for x,y,z. Then ...,
Hyperfuzzy
1 / 5 (2) Feb 04, 2016
I would limit the search with easy to find elements and compounds, and my methodology and cost for assimilation.

Or maybe apply this technology to molecular control on the fly. With the right pocket tools, capable to sense anything.

I'm just talking about what we know and how we use our energy. Anyway, I would begin with a clear definition of what I am looking for. Simple, and curl of E or a dq/dt are obviously related. Seems more like how do we do this curl in the field with no atomic wobbling. That makes since, doesn't it? Yea, use a computer, yea, pretty large search, why not multiple computers, explain everything!
Hyperfuzzy
1 / 5 (2) Feb 04, 2016
-infinity <= t <= +infinity and compositions
PhysicsMatter
not rated yet Feb 05, 2016
It is commendable that research on superconductivity is being undertaken since it is a part of critical technologies for further development of civilization unless we opt for forceful depression of demographics.
Bu the fundamental obstacle in those efforts is lack adequate theory, that would provide models that could be technologically adopted.

One must start from a model what superconductivity really is starting from revising out numerous and different theories of conductivity itself depending on application.

We need general unified theory of conductivity, non-conductors, semi-conductors, metal conductors, superconductors and plasma conductors.

Otherwise it is just guessing.
Phys1
4 / 5 (4) Feb 05, 2016
"A magnet levitating above a cuprate high temperature superconductor."
Should be "A cuprate high temperature superconductor levitating above a magnet.".
Eikka
4.8 / 5 (6) Feb 05, 2016
"A magnet levitating above a cuprate high temperature superconductor."
Should be "A cuprate high temperature superconductor levitating above a magnet.".


No, that's the superconductor at the bottom.

Its demonstrating an effect known as flux pinning, which is where the magnetic field penetrates through the superconductor only in quantisized "packets" or flux tubes. Elsewhere the material demonstrates perfect diamagnetism and forces the field to go around itself.

The magnet stays put because the superconductor grabs a hold of the magnetic field.
It's like pushing your fingers through a grate - the flux lines are stuck in the tubes and would have to break and re-connect for the magnet to move around. If you push the magnet hard enough, that will happen.
Phys1
4.8 / 5 (4) Feb 05, 2016
@Eikkas
You are right.
promile
Feb 05, 2016
This comment has been removed by a moderator.
promile
Feb 05, 2016
This comment has been removed by a moderator.
promile
Feb 05, 2016
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bschott
5 / 5 (1) Feb 05, 2016
@Eikka

Good job explaining how this physics works to the confused.
promile
Feb 05, 2016
This comment has been removed by a moderator.
RealityCheck
not rated yet Feb 05, 2016
Hi promile. :)

Eikka said:
The magnet stays put because the superconductor grabs a hold of the magnetic field.


promile said:
OK, try to explain why this superconductor can move https://youtu.be/...nxw?t=31 above magnets...
The 'pinning' effect which Eikka alluded to is what would slow the motion unless new impetus is supplied by the puck-accelerator spinning-wheels system. The 'pinning' is what keeps the puck aligned at a fixed average distance from the magentic track surface/sides; also the 'joints' between the 'segmented' magnetic track represent where the puck moves across what would be the 'pinning effect' at those edge-boundaries of each of the magnetic segments fields 'merging' at those boundaries (but not perfectly, so there is a 'pinning force' component associated with each closest near-field to each magnetic surface there; but the motion seems 'smooth' because the 'pinning effect' is lower there; easily overcome by puck's momentum). :)
promile
Feb 05, 2016
This comment has been removed by a moderator.
RealityCheck
not rated yet Feb 05, 2016
Hi promile.:)
Actually the motion https://www.youtu...Y2bm-W50 even when the superconductor is very thin and it's momentum close to zero.
Is that also with a segmented magnetic track? If so, then the impetus provided by any 'puck accelerating' mechanism will very soon be exhausted by the same 'pinning' tendencies and the associated decelerations imparted at each 'junction crossing'.

Also, the 'pinning' effects will be less strong because of the correspondingly lesser scale superconducting/magnet material bulk/thickness etc dimensions. So the 'smoothness' is always an illusion, depending on the applicable 'step responses/effects' encountered by the set-up parameters/context and the motional impetus along the track which has been provided externally. Are you thinking of 'contiguous track' scenarios where the whole track is 'smooth' and without 'joints'? :)

Note: in your video ref, the momentum is provided by gravity when he tips the setup off-level.
Eikka
5 / 5 (2) Feb 06, 2016
OK, try to explain why this superconductor can move so smoothly above magnets...


It depends on the configuration.

The "flux lines" of a magnetic field are not real entities - they're not like invisible cotton strings - they're abstractions invented to simplify thinking about the matter, and don't actually exist. The field however does exist.

As long as the field through the superconduct stays constant in direction and magnitude, the magnet and superconductor can move relative to one another. That's why if you place a circular magnet above a superconductor, it can spin. If the magnet is shaped square, it can't spin. If you have a long magnet that is magnetized on the edge, the superconductor can move in a line - along the constant field region where the magnetic field through the superconductor does not change.

And of course, the magnetic field itself is "pliable" and can be stretched and bent to a degree, so the pinned magnet can move around as if on a spring.
Eikka
5 / 5 (2) Feb 06, 2016
Basically, a magnet placed end-on above a superconductor is pinned in place very well because its magnetic field through the flux tubes in the superconducting material go like a many-pronged fishhook.

It's lost all the degrees of freedom because tilting or translating the magnet would change the direction and magnitude of at least some of the field lines, and that won't happen until you apply enough force to break and reconnect the field to a different configuration.

It needs the force because the field can't change its shape smoothly through the superconductor - it happens in discrete steps, and between the steps the field has to go around the long way, which is like rolling a cart down the road and hitting a speed bump - you have to push to go over, otherwise you're stuck.

So the magnet levitates because it's like a cart stuck between two sleeping policemen. Gravity is not enough to push it over one way or the other.
Eikka
5 / 5 (2) Feb 06, 2016
Mind you, there's also ordinary diamagnetic levitation which does not depend on the flux pinning quantum effect. A small piece of pyrolytic graphite will levitate above a magnet at room temperature because it resists the magnetic field going through it.

That effect doesn't depend on the direction of the magnetic field, it's only about the magnetic field pushing the material away, and it's stable levitation because the material itself isn't magnetic so it doesn't try to flip around and slam into the magnets.

In a superconducting levitator, both effects are at play at once.
promile
Feb 06, 2016
This comment has been removed by a moderator.
Phys1
5 / 5 (1) Feb 06, 2016
Mind you, there's also ordinary diamagnetic levitation which does not depend on the flux pinning quantum effect.

Here a sensational demonstration of diamagnetic levitation.

https://www.youtu...yB-O5i6E
Eikka
5 / 5 (1) Feb 06, 2016
That effect doesn't depend on the direction of the magnetic field
How can you explain after then, that the stable levitation of pyrolitic graphite can be achieved only with certain orientation of magnets bellow it?


You don't need any certain orientation or configuration. All you need for a stable configuration is that the magnetic field flux density distribution is shaped slightly like a bowl in the direction of gravity, so the piece of graphite doesn't slip off the side.

The diamagnetic material is being pushed away from the densest field regardless of which way the field is going in the same sense as how an air bubble rises or a boat floats in water - the diamagnetic material displaces and distorts the magnetic field, which causes it to push back at the diamagnetic material.

Eikka
5 / 5 (1) Feb 06, 2016
Here a sensational demonstration of diamagnetic levitation.


Water is somewhat diamagnetic. The frog floats over an incredibly powerful electromagnet.

The same effect can be demostrated with water in a petri dish and a sufficiently strong neodymium magnet button under the dish. The water is repelled upwards and that forms a slight bump on the surface that can be seen by eye if the magnet is strong enough. For weaker magnets, reflecting light off of the surface reveals the curvature.

You can even place the petri dish on an overhead projector, and when a magnet is brought close, the water surface distorts and that causes it to act like a lens, which can be seen in the projection.
Eikka
5 / 5 (1) Feb 06, 2016
The petri dish experiment also reveals why you can't levitate a piece of graphite over a single magnet - because the field density distribution above the magnet is shaped like a hill, and the piece of graphite will slide down the side. WIth four magnets in a square, there's four hills and a valley in the middle, where the graphite can be trapped.

But of course if the graphite was shaped like a hat, with a low center of gravity, or a ring, it would sit and hover quite happily on the field of a single magnet.

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