Mathis on Graphene? Any hints?

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Post by Cr6 on Sun Jun 16, 2019 9:33 pm

Graphene nanoribbons

Graphene nanoribbons (GNRs, also called nano-graphene ribbons or nano-graphite ribbons) are strips of graphene with width less than 50 nm. Graphene ribbons were introduced as a theoretical model by Mitsutaka Fujita and coauthors to examine the edge and nanoscale size effect in graphene.[2][3][4]

Mathis on Graphene?  Any hints?  - Page 5 330px-B-doped_graphene_nanoribons

Nanotomy


Large quantities of width-controlled GNRs can be produced via graphite nanotomy,[5] where applying a sharp diamond knife on graphite produces graphite nanoblocks, which can then be exfoliated to produce GNRs. GNRs can also be produced by "unzipping" or axially cutting nanotubes.[6] In one such method multi-walled carbon nanotubes were unzipped in solution by action of potassium permanganate and sulfuric acid.[7] In another method GNRs were produced by plasma etching of nanotubes partly embedded in a polymer film.[8] More recently, graphene nanoribbons were grown onto silicon carbide (SiC) substrates using ion implantation followed by vacuum or laser annealing.[9][10][11] The latter technique allows any pattern to be written on SiC substrates with 5 nm precision.[12]

Epitaxy

GNRs were grown on the edges of three-dimensional structures etched into silicon carbide wafers. When the wafers are heated to approximately 1,000 °C (1,270 K; 1,830 °F), silicon is preferentially driven off along the edges, forming nanoribbons whose structure is determined by the pattern of the three-dimensional surface. The ribbons had perfectly smooth edges, annealed by the fabrication process. Electron mobility measurements surpassing one million correspond to a sheet resistance of one ohm per square— two orders of magnitude lower than in two-dimensional graphene.[13]

https://en.wikipedia.org/wiki/Graphene_nanoribbon

Silicene Transistors

The U.S. Army Research Laboratory has been supporting research on silicene since 2014. The stated goals for research efforts were to analyze atomic scale materials, such as silicene, for properties and functionalities beyond existing materials, like graphene.[40] In 2015, Deji Akinwande, led researchers at the University of Texas, Austin in conjunction with Alessandro Molle's group at CNR, Italy, and collaboration with U.S. Army Research Laboratory and developed a method to stabilize silicene in the air and reported a functional silicene field effect transistor device. An operational transistor’s material must have bandgaps, and functions more effectively if it possesses a high mobility of electrons. A bandgap is an area between the valence and conduction bands in a material where no electrons exist. Although graphene has a high mobility of electrons, the process of forming a bandgap in the material reduces many of its other electric potentials.[41]

https://en.wikipedia.org/wiki/Silicene
https://en.wikipedia.org/wiki/2D_silica
https://en.wikipedia.org/wiki/Borophene
https://en.wikipedia.org/wiki/Germanene
https://en.wikipedia.org/wiki/Stanene
https://en.wikipedia.org/wiki/Plumbene

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Post by Cr6 on Fri Sep 06, 2019 1:01 am

"P-wave states"...hmm could that just be the alignment of Mathis' charge field?

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Graphene's Superconductive Power Has Finally Been Unlocked, And It's Crazier Than We Expected
FIONA MACDONALD
20 JAN 2017

It's official: graphene has been made into a superconductor in its natural state - which means electrical current can flow through it with zero resistance.

Last year, physicists managed to do this by doping graphene with calcium atoms, but this is the first time researchers have achieved superconductivity in the material without having to alter it. And the results so far show that the material achieves an incredibly rare type of superconductivity that's even crazier and more powerful than scientists expected.

The new research is a big deal even for a material as innately impressive as graphene, seeing as superconductivity is the key to more efficient electronics, better power grids, and new medical technology.

"It has long been postulated that, under the right conditions, graphene should undergo a superconducting transition, but can't," said one of the researchers, Jason Robinson from the University of Cambridge in the UK.

Now, he says his team has managed to awaken that ability. And it appears graphene isn't just a normal superconductor - it could be conducting current with no resistance as a result of an unconfirmed and elusive type of superconductivity called p-wave state. Further research is needed to confirm this result, but it's a pretty intriguing possibility.

Already an over-achiever, graphene is a two-dimensional sheet of carbon atoms that's super flexible, harder than diamond, and stronger than steel.

But since its discovery in 2004, researchers have suspected that graphene might also have the ability to be a superconductor - which means it could shuttle electrons through it with no resistance at all.

Even materials that are good conductors are still inefficient in comparison to superconductors - for example, energy companies lose about 7 percent of their energy as heat as a result of resistance in the grid.

We already use superconducting materials to create the strong magnetic fields needed in MRI machines and maglev trains, but right now, these materials only become superconductive at temperatures of around –269 degrees Celsius (–452.2 degrees Fahrenheit), which is incredibly expensive, and not exactly practical.

If we could find a way to achieve superconductivity sustainably and at high temperatures, it would open up a the possibility of supercomputers that run without resistance and more efficient medical technology - and graphene is often thought of as a prime candidate for achieving this, given all of its other weird and wonderful properties.

Researchers succeeded in making graphene a superconductor last year by inserting calcium atoms into its lattice. And other teams have achieved a similar result by placing it on a superconducting material.

But in the new study, researchers from the University of Cambridge were able to activate the dormant potential of graphene without it being influenced by another material.

"Placing graphene on a metal can dramatically alter the properties so it is technically no longer behaving as we would expect," said one of the team, Angelo di Bernardo.

"What you see is not graphene's intrinsic superconductivity, but simply that of the underlying superconductor being passed on."

Instead, the team achieved superconductivity by coupling it with a material called praseodymium cerium copper oxide (PCCO).

That might sound similar to what happened in previous experiments - after all, they're still putting graphene on top of another material - but the difference here is that PCCO is a type of superconducting material called a cuprate, which has well-understood electronic properties.

So the team was able to clearly distinguish the superconductivity in PCCO from the superconductivity in graphene.

And what they saw was crazier than they'd expected.

Superconductivity occurs when electrons pair up and travel more efficiently through a material.

The spin alignment, or symmetry, of these electron pairs changes depending on the type of superconductivity involved. For example, in PCCO, the electrons pair up with a spin state that's antiparallel, which is called d-wave state.

But what the team saw happening in graphene was very different - they found evidence of a rare and still unverified type of superconductivity called p-wave state occurring.

"What we saw in the graphene was, in other words, a very different type of superconductivity than in PCCO," said Robinson.

"This was a really important step because it meant that we knew the superconductivity was not coming from outside it and that the PCCO was therefore only required to unleash the intrinsic superconductivity of graphene."

It remains unclear exactly what kind of superconductivity the team unleashed in graphene - but if it's confirmed that it really is the elusive p-wave form, it could prove once and for all that this type of superconductivity exists, and allow researchers to study it properly for the first time.

P-wave superconductivity was first proposed in 1994, when Japanese researchers found evidence of it occurring in a crystal material called strontium ruthenate. But the crystal is too bulky to study it well enough to achieve the type of proof scientists need to confirm that the state exists.

If it's happening in graphene, it would be a lot easier to investigate.
....
(more at link)

https://www.sciencealert.com/graphene-s-superconductive-power-has-finally-been-unlocked-and-it-s-crazier-than-we-expected

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Post by Cr6 on Fri Sep 06, 2019 1:02 am

Keep in mind these papers:
1/13/18, What Rutherford really Proved about the Electron. Also more information about the positron.
http://milesmathis.com/electron.pdf

1/5/18, Graphene. Where we see all the mainstream explanations are wrong. Why? Because they are based on electron bonding theory, which is a fudge from the first word.
http://milesmathis.com/graphene.pdf


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Unconventional superconductivity in magic-angle graphene superlattices

Yuan Cao, Valla Fatemi, Shiang Fang, Kenji Watanabe, Takashi Taniguchi, Efthimios Kaxiras & Pablo Jarillo-Herrero

Nature volume 556, pages 43–50 (05 April 2018) | Download Citation

Abstract


The behaviour of strongly correlated materials, and in particular unconventional superconductors, has been studied extensively for decades, but is still not well understood. This lack of theoretical understanding has motivated the development of experimental techniques for studying such behaviour, such as using ultracold atom lattices to simulate quantum materials. Here we report the realization of intrinsic unconventional superconductivity—which cannot be explained by weak electron–phonon interactions—in a two-dimensional superlattice created by stacking two sheets of graphene that are twisted relative to each other by a small angle. For twist angles of about 1.1°—the first ‘magic’ angle—the electronic band structure of this ‘twisted bilayer graphene’ exhibits flat bands near zero Fermi energy, resulting in correlated insulating states at half-filling. Upon electrostatic doping of the material away from these correlated insulating states, we observe tunable zero-resistance states with a critical temperature of up to 1.7 kelvin. The temperature–carrier-density phase diagram of twisted bilayer graphene is similar to that of copper oxides (or cuprates), and includes dome-shaped regions that correspond to superconductivity. Moreover, quantum oscillations in the longitudinal resistance of the material indicate the presence of small Fermi surfaces near the correlated insulating states, in analogy with underdoped cuprates. The relatively high superconducting critical temperature of twisted bilayer graphene, given such a small Fermi surface (which corresponds to a carrier density of about 1011 per square centimetre), puts it among the superconductors with the strongest pairing strength between electrons. Twisted bilayer graphene is a precisely tunable, purely carbon-based, two-dimensional superconductor. It is therefore an ideal material for investigations of strongly correlated phenomena, which could lead to insights into the physics of high-critical-temperature superconductors and quantum spin liquids.

https://www.nature.com/articles/nature26160

-----------------


Insulator or superconductor? Physicists find graphene is both

When rotated at a "magic angle," graphene sheets can form an insulator or a superconductor.


Jennifer Chu | MIT News Office
March 5, 2018
Press Inquiries


It’s hard to believe that a single material can be described by as many superlatives as graphene can. Since its discovery in 2004, scientists have found that the lacy, honeycomb-like sheet of carbon atoms — essentially the most microscopic shaving of pencil lead you can imagine — is not just the thinnest material known in the world, but also incredibly light and flexible, hundreds of times stronger than steel, and more electrically conductive than copper.

Now physicists at MIT and Harvard University have found the wonder material can exhibit even more curious electronic properties. In two papers published today in Nature, the team reports it can tune graphene to behave at two electrical extremes: as an insulator, in which electrons are completely blocked from flowing; and as a superconductor, in which electrical current can stream through without resistance.

Researchers in the past, including this team, have been able to synthesize graphene superconductors by placing the material in contact with other superconducting metals — an arrangement that allows graphene to inherit some superconducting behaviors. This time around, the team found a way to make graphene superconduct on its own, demonstrating that superconductivity can be an intrinsic quality in the purely carbon-based material.

The physicists accomplished this by creating a “superlattice” of two graphene sheets stacked together — not precisely on top of each other, but rotated ever so slightly, at a “magic angle” of 1.1 degrees. As a result, the overlaying, hexagonal honeycomb pattern is offset slightly, creating a precise moiré configuration that is predicted to induce strange, “strongly correlated interactions” between the electrons in the graphene sheets. In any other stacked configuration, graphene prefers to remain distinct, interacting very little, electronically or otherwise, with its neighboring layers.

The team, led by Pablo Jarillo-Herrero, an associate professor of physics at MIT, found that when rotated at the magic angle, the two sheets of graphene exhibit nonconducting behavior, similar to an exotic class of materials known as Mott insulators. When the researchers then applied voltage, adding small amounts of electrons to the graphene superlattice, they found that, at a certain level, the electrons broke out of the initial insulating state and flowed without resistance, as if through a superconductor.

“We can now use graphene as a new platform for investigating unconventional superconductivity,” Jarillo-Herrero says. “One can also imagine making a superconducting transistor out of graphene, which you can switch on and off, from superconducting to insulating. That opens many possibilities for quantum devices.”

A large-scale interpretation of the moiré patterns formed when one graphene lattice is slightly rotated at a “magic angle,” with respect to a second graphene lattice.

A 30-year gap

A material’s ability to conduct electricity is normally represented in terms of energy bands. A single band represents a range of energies that a material’s electrons can have. There is an energy gap between bands, and when one band is filled, an electron must embody extra energy to overcome this gap, in order to occupy the next empty band.

A material is considered an insulator if the last occupied energy band is completely filled with electrons. Electrical conductors such as metals, on the other hand, exhibit partially filled energy bands, with empty energy states which the electrons can fill to freely move.

Mott insulators, however, are a class of materials that appear from their band structure to conduct electricity, but when measured, they behave as insulators. Specifically, their energy bands are half-filled, but because of strong electrostatic interactions between electrons (such as charges of equal sign repelling each other), the material does not conduct electricity. The half-filled band essentially splits into two miniature, almost-flat bands, with electrons completely occupying one band and leaving the other empty, and hence behaving as an insulator.

“This means all the electrons are blocked, so it’s an insulator because of this strong repulsion between the electrons, so nothing can flow,” Jarillo-Herrero explains. “Why are Mott insulators important? It turns out the parent compound of most high-temperature superconductors is a Mott insulator.”

(more at link)
https://news.mit.edu/2018/graphene-insulator-superconductor-0305
----------------------------

p-wave triggered superconductivity in single-layer graphene on an electron-doped oxide superconductor


A. Di Bernardo, O. Millo, M. Barbone, H. Alpern, Y. Kalcheim, U. Sassi, A. K. Ott, D. De Fazio, D. Yoon, M. Amado, A. C. Ferrari, J. Linder & J. W. A. Robinson
Nature Communications volume 8, Article number: 14024 (2017) | Download Citation


Abstract


Electron pairing in the vast majority of superconductors follows the Bardeen–Cooper–Schrieffer theory of superconductivity, which describes the condensation of electrons into pairs with antiparallel spins in a singlet state with an s-wave symmetry. Unconventional superconductivity was predicted in single-layer graphene (SLG), with the electrons pairing with a p-wave or chiral d-wave symmetry, depending on the position of the Fermi energy with respect to the Dirac point. By placing SLG on an electron-doped (non-chiral) d-wave superconductor and performing local scanning tunnelling microscopy and spectroscopy, here we show evidence for a p-wave triggered superconducting density of states in SLG. The realization of unconventional superconductivity in SLG offers an exciting new route for the development of p-wave superconductivity using two-dimensional materials with transition temperatures above 4.2 K.


https://www.nature.com/articles/ncomms14024


Last edited by Cr6 on Fri Sep 06, 2019 1:53 am; edited 1 time in total

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Post by Cr6 on Fri Sep 06, 2019 1:12 am

In Miles' words:

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1/5/18, Graphene. Where we see all the mainstream explanations are wrong. Why? Because they are based on electron bonding theory, which is a fudge from the first word.
http://milesmathis.com/graphene.pdf

We are told that electrons propagating through Graphene lose their mass, becoming quasi-particles, but
that is absurd. What really happens is that the electrons are spin-stripped by the material, becoming
photons. The reason they have to be described currently by the 2-D Dirac equation rather than the
Schrodinger equation is that the Schrodinger equation is faulty, especially regarding spin ½ particles.
Since the whole theory behind spin ½ is also faulty, we see where the mess came from. But why
would Graphene spin-strip an electron down to a real photon?
Again because the applied current is
moving opposite to the internal current of Graphene. Charge can move both directions here, but
electrons can't. The electrons they are talking about are electrons that came in with the applied current,
so they are moving with what we are calling the anticharge here. We will say they are spinning right.
But the internal charge profile of the Graphene, as created by the metal, is charge, or left spinning.
Therefore, when the introduced electron hits the field of the Graphene, it will be spun down. If its
outer spin is spun down completely, this is the same as a spin-strip. That spin is gone. An electron that
loses its outer spin becomes a photon. Therefore, under the right circumstances, we should see
Graphene “producing” X-rays. And guess what, it does. At that link to phys.org, we are told that
electrons moving through Graphene plasmons cause them to release X-rays. But the electrons aren't
releasing X-rays, they are becoming X-rays. That would be pretty easy to prove, since they now have
electron counters. All they have to do is count electrons. They will find that the X-ray production
leads to an electron reduction.
--------

Also:
http://milesmathis.forumotion.com/t259-graphene-s-crazier-than-we-thought-can-handle-1000-times-more-current-than-regular-material
http://milesmathis.forumotion.com/t292-newly-discovered-phenomenon-shows-electrons-can-move-much-faster-than-expected

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