Talk-Polywell.org

Giving Graphene a Good Stretch
http://physics.aps.org/synopsis-for/10. ... 115.245501

Programmable Extreme Pseudomagnetic Fields in Graphene by a Uniaxial Stretch
http://arxiv.org/abs/1511.02389

So, if you folded it in the middle, wrapping it a half turn around a nonconducting nanocylinder (with a large enough diameter to keep the two parallel graphene halves from interfering), then pulled on both ends of the cylinder in one direction and the two graphene ends in the opposite direction, the B vectors normal to the graphene would combine, instead of canceling in the far field. Then, form a macroscopic array of many of these units, all aligned in one direction.

It is not a Magnetic Field, is a Pseudo-Magnetic Field.

It means that the electron clouds of the atoms of the material subjected to the strain process will behave AS IF it was immersed in a strong magnetic field.
Physically speaking, the stretching action in the Graphene changes the LANDAU quantization levels of the material thus increasing it's electron density (and hence changing its electronic properties). Because the same happens also when we immerse a material in a strong and uniform magnetic field than we can actually study the electronic properties of that material at magnetic fields levels that we can't reach yet.

Extremely interesting phenomena for researching Graphene properties, but no real Magnetic Field is generated.

Giorgio wrote:It means that the electron clouds of the atoms of the material subjected to the strain process will behave AS IF it was immersed in a strong magnetic field.
...
but no real Magnetic Field is generated.

So, electrons behaving AS IF immersed in a strong magnetic field will move generally in circles, giving rise to an actual magnetic field.
I concede that the actual field would likely be lower in magnitude than the imposed pseudomagnetic field. Sort of like the losses expected in an electric motor or generator, but with nano/quantum/lattice complications.

It would be interesting to know the conversion efficiency, strain energy vs. B field energy.

I don't know what thus means. Is this the B fie3ld inside the material or outside in free space (~equivalent to air to various levels of vacuum)? Inside a material the B fields may be as much (or more?) than a thousand times higher. The B field within the high permeability core of a transformer may be hundreds of Tesla or more, while the B field nearby in free space may be a small fraction of a Tesla. It is this outside B field that is important for acting on a plasma.

The only implication that I see with a (very) superficial understanding is if these properties effect the electrical conductivity of a wire so that the wires can be smaller with resultant more amp- turns that fit within a cooled can- that generates a B field that propagates through free space. I have heard stories of graphene being a better electrical conductor than copper, perhaps by as much as 100 fold. These claims seem tentative though. If further understanding can lead to bulk production of useful high conductivity wires or ribbons without the need for cryogenic cooling/ superconducting conditions, then a 100 fold improvement may be more useful than an infinate increase with superconductors, especially with current carrying capacity considerations and other engineering issues...

Dan Tibbets

DeltaV wrote:

Giorgio wrote:It means that the electron clouds of the atoms of the material subjected to the strain process will behave AS IF it was immersed in a strong magnetic field.
...
but no real Magnetic Field is generated.

So, electrons behaving AS IF immersed in a strong magnetic field will move generally in circles, giving rise to an actual magnetic field.
I concede that the actual field would likely be lower in magnitude than the imposed pseudomagnetic field. Sort of like the losses expected in an electric motor or generator, but with nano/quantum/lattice complications.


It would be interesting to know the conversion efficiency, strain energy vs. B field energy.

I am not sure I understand what you are trying to point out.

If you are referring to the possibility to have a Quantum Hall Effect with a zero value REAL B Field, than it is indeed a possibility, but so far is a purely a theoretical one.

If you are referring to the possibility that they actually generated a "Real" Magnetic field by stranding of Graphene, than no. If that happened it would have made headlines in every scientific publication around the world as a new Magnetostrictive material and probably granted a Nobel to the discoverer. If something is "Pseudo (Virtual)" than it is not "Real".

D Tibbets wrote:I don't know what thus means. Is this the B fie3ld inside the material or outside in free space (~equivalent to air to various levels of vacuum)? Inside a material the B fields may be as much (or more?) than a thousand times higher. The B field within the high permeability core of a transformer may be hundreds of Tesla or more, while the B field nearby in free space may be a small fraction of a Tesla. It is this outside B field that is important for acting on a plasma.

The only implication that I see with a (very) superficial understanding is if these properties effect the electrical conductivity of a wire so that the wires can be smaller with resultant more amp- turns that fit within a cooled can- that generates a B field that propagates through free space. I have heard stories of graphene being a better electrical conductor than copper, perhaps by as much as 100 fold. These claims seem tentative though. If further understanding can lead to bulk production of useful high conductivity wires or ribbons without the need for cryogenic cooling/ superconducting conditions, then a 100 fold improvement may be more useful than an infinate increase with superconductors, especially with current carrying capacity considerations and other engineering issues...

Dan Tibbets

The stranding generated deformations in the lattice structure of the Graphene in bubble like shapes (few nanometers wide) that mimic the action that an equivalent strong B Field would have on the Graphene according theoretical predictions. Hence the "Pseudo Magnetic" definition.

Even if this research field is just few years old I doubt this phenomena could be ever used for improving electrical conductivity over long lines of wires.

I think this is the first report of this phenomena in 2005:
Graphene Under Strain Creates Gigantic Pseudo-Magnetic Fields

Giorgio wrote:a zero value REAL B Field

It is zero value in the far field, for an unfolded device.

DeltaV wrote:

Giorgio wrote:a zero value REAL B Field

It is zero value in the far field, for an unfolded device.

Than you imply the existence of a REAL and NON ZERO value B field in the localized deformation, but as I said (and as the researchers reported) this has not been observed.

Giorgio wrote:It means that the electron clouds of the atoms of the material subjected to the strain process will behave AS IF it was immersed in a strong magnetic field.

So this statement is wrong? The pseudomagnetic field does not curve electron paths, leading to a real magnetic field?

DeltaV wrote:

Giorgio wrote:It means that the electron clouds of the atoms of the material subjected to the strain process will behave AS IF it was immersed in a strong magnetic field.

So this statement is wrong? The pseudomagnetic field does not curve electron paths, leading to a real magnetic field?

The statement is right. You are interpreting it wrong or you are not getting the "AS IF" part.
You can have same behavior (or deformation) in a material from different causes (or forces). But just because the end result is the same it does not mean that the cause that generated it is the same nor that it will give rise to the same secondary effects (like the creation of a Magnetic Field).

As I pointed out in a previous post, there are already classes of materials that react to a strain process by generating a magnetic field and vice-versa. They are called Magnetostrictive material and are mainly used as transducers.
The discovery of a new class of Magnetostrictive materials based on Graphene would be a huge discovery.
This is not the case, unfortunately.

Strain process in Graphene simply create a local deformations AS IF it was immersed in a strong magnetic field but without any measurement of a real Magnetic Field. Hence the name Pseudo-Magnetic, or Fake magnetic, or Virtual magnetic, but anyhow not real.

Giorgio wrote:Strain process in Graphene simply create a local deformations AS IF it was immersed in a strong magnetic field

Do your "local deformations" affect electrons? Yes or No? You can't have it both ways (except in the quantum realm, and I'm a classical guy).

If the answer is Yes, then are electron paths affected (curved) by the pseudomagnetism?

If the answer to that is Yes, then do the curving electrons produce actual magnetic flux lines (whether or not said flux cancels in the far field)?

Giorgio wrote:but without any measurement of a real Magnetic Field. Hence the name Pseudo-Magnetic, or Fake magnetic, or Virtual magnetic, but anyhow not real.

In the device pictured above, any induced actual flux would cancel in the far field and be undetectable without nano probes.

Hence my folding scheme.

Which could be futile if electron angular (orbital) momentum conservation imposes a (pseudo)magnetic sign change in one half of the folded device. But that would change odd symmetry to even symmetry, so maybe instead the pseudomagnetism would go to zero as the device is folded and the strain energy would just manifest as a temperature increase instead of as B field potential energy. But that extra heat would radiate away as infrared photons...

DeltaV wrote:

Giorgio wrote:Strain process in Graphene simply create a local deformations AS IF it was immersed in a strong magnetic field

Do your "local deformations" affect electrons? Yes or No? You can't have it both ways (except in the quantum realm, and I'm a classical guy).

Every deformation effects electrons, but this does not mean that every effect on the electrons generate a measurable magnetic effect.

DeltaV wrote:If the answer is Yes, then are electron paths affected (curved) by the pseudomagnetism?

This is the point you are not focusing. How can something PSEUDO (Unreal, Virtual) effect a path of something REAL (the electron cloud)?
Is like if you tell me than you modify your home in a CAD software and when you go out of the door you expect to actually see the modifications you did on the CAD.

Once you focus the point that there is no real magnetic field involved than all the other points you mentioned can't exist.
Once again, if a real and measurable magnetic effect was generated from stranding of Graphene, it would have been a huge discovery with immediate practical applications that the researchers would have pointed out straight away.

Giorgio wrote:Every deformation effects electrons, but this does not mean that every effect on the electrons generate a measurable magnetic effect

It is well known that a strong, real, magnetic field will curve electron paths. If the pseudomagnetic field, up to hundreds of pseudo-Tesla, does not curve electron paths, then calling it pseudomagnetic seems mendacious.

Giorgio wrote:Once you focus the point that there is no real magnetic field involved than all the other points you mentioned can't exist.

Whether or not pseudo B actually induces local, real B, one should expect to measure zero real B in the far field for the unfolded device.

Saying, however, that there is no local real B because nothing is measured in the far field is disingenuous.

Giorgio wrote:Once again, if a real and measurable magnetic effect was generated from stranding of Graphene, it would have been a huge discovery with immediate practical applications that the researchers would have pointed out straight away.

If by "stranding" you mean "stretching", are you saying that someone has measured the local field with a nano probe, inside the effective span of the expected odd-symmetrical cancellation?

My guess is that any B field measurement only looked at the far field.

DeltaV wrote:

Giorgio wrote:Every deformation effects electrons, but this does not mean that every effect on the electrons generate a measurable magnetic effect

It is well known that a strong, real, magnetic field will curve electron paths. If the pseudomagnetic field, up to hundreds of pseudo-Tesla, does not curve electron paths, then calling it pseudomagnetic seems mendacious.

You are making a big confusion, mixing the effect with the cause and vice-versa.
Stranding of the Graphene will make the electrons to turn in a circle, as they would in a magnetic field, BUT WITHOUT the magnetic field.
Cause: Magnetic Field -- Effect: Electron Density increases in uniform way on the sample
Cause: Stranding -- Effect: Electron Density increase in localized area (bubbles on sample), and the quoted paper proposes a way to make it uniform over all the area of the sample

So, the "Magnetic Field" and the "Stranding" are the CAUSE that generated the requested EFFECT of Electron Density Increase over the surface of the sample.
Why the use the term "PseudoMagnetic"? It simple. Because the action of "Stranding" of the material will cause an effect in the samples similar to the one of a real "Magnetic effect". To better express the effect that the Stranding was creating on the sample they they called it "PseudoMagnetic Effect", so every scientist could quickly understand that it is an effect similar to the one that a REAL magnetic field would have generated.
The importance of the experiment is that it allows to get increased Electron Density (EFFECT) in the sample "AS IF" it was immersed in a Magnetic Field (CAUSE) of several hundred Tesla, without the need for a real Magnetic Field, meaning we can have opening of an energy gap in the lattice structure of the sample without need for a strong magnetic field.

Read the paper I linked before, is all expressed quite well.

Giorgio wrote:You are making a big confusion, mixing the effect with the cause and vice-versa.

No, I am not. You are the confused one.

I may certainly be overlooking quantum effects, as I implied earlier.

The transition between, say, "folding" a classical, opposite-chirality coil system, driven by electric potential from a battery, so that the chirality becomes the same... and folding a quantum, opposite-chirality electron-orbit system, driven by electric potential from stretching graphene, may or may not hold.

But I am not confusing cause and effect in the hypothesized system.

You are the one denying that electrons, that are supposed to behave AS IF they are in a real magnetic field, will curve their paths and produce a real magnetic field as all such curving electrons must do. There is no assertion here that the real field will have the same magnitude as the pseudo field (the conversion efficiency mentioned earlier - one possibility is zero % efficient).

I'll repeat it one final time:

Cause 1-- straining of graphene lattice -->
Effect 1a -- electrons curve AS IF in a high B field, due to changed electric fields;
Effect 1b -- curved electron paths produce a real B field, normal to the 2-D lattice, vector signs in agreement with the pseudomagnetic scalar signs, real B cancels in the far field due to odd symmetry.

Cause 2 -- strained graphene lattice is folded in a 3rd dimension by pi radians about its center -->
Effect 2 -- assuming quantum physics allows, the real B field survives and no longer cancels in the far field, since the initial odd symmetry of the curving-electron-caused real B vectors leads, after folding, to non-cancellation.