Scientists find unusual electrons that go with the flow

Jul 14, 2010
This view provides a look into the heart of a scanning tunneling microscope in the specially designed Princeton Nanoscale Microscopy Laboratory, where highly accurate measurements at the atomic scale are possible because sounds and vibrations, through a multitude of technologies, are kept to a minimum. Credit: Princeton University, Office of Communications, Brian Wilson

On a quest to discover new states of matter, a team of Princeton University scientists has found that electrons on the surface of specific materials act like miniature superheroes, relentlessly dodging the cliff-like obstacles of imperfect microsurfaces, sometimes moving straight through barriers.

The Princeton work represents the first time such behavior of electrons has been tracked and recorded, and hints at the possibilities of speeding up that process information by flow of electrons between different devices. The new materials potentially could break the bottleneck that occurs when metallic interconnects get so small that even the tiniest atomic imperfection hinders their performance.

Physics professor Ali Yazdani and his team observed the extraordinary physics behavior in a "topological state" on a microscopic wedge of the metal antimony. The work is reported in the July 15 issue of Nature.

Normally, electron flow in materials is impeded by imperfections -- seemingly slight edges and rifts act like cliffs and crevasses in this microscopic world, blocking electrons in their path. Recent theories, however, predict that electrons on the surface of some compounds containing elements such as antimony can be immune to such disruptions in their flow. The connectivity in their flow, Yazdani said, stems from a special form of electron wave that seemingly alters the pattern of flow around any imperfection.

Many of the "topological" materials, such as antimony, have been important in the world economy; however, their unusual surface conduction previously had not been examined. Part of the challenge had been the difficulty in measuring the flow of electrons just at the surface, a task that was accomplished by the Princeton group using a specialized that enables precise visualization of electrons at the surface of materials.

"Material imperfections just cannot trap these surface electrons," said Yazdani, whose pioneering explorations of the behavior of electrons in unusual materials in his Jadwin Hall laboratories has consistently yielded new insights. "This demonstration suggests that surface conduction in these compounds may be useful for high-current transmission even in the presence of atomic scale irregularities -- an electronic feature sought to efficiently interconnect nanoscale devices."

An electron is a subatomic particle that carries a negative electric charge. It orbits an atom's nucleus and is bound to it by electromagnetic forces. Electrons can hop between atoms in a limited number of materials, such as crystals, and move freely in their interior or on the surface.

These free electrons are responsible for the generation of electric current, playing a central role in numerous applications related to industry, science and medicine, including providing the current for modern electronic devices. For most metals, electrons in the interior carry most of the electrical current, with the electrons at the surface being only weakly mobile.

At a given temperature, materials possess a measurable conductivity that determines the intensity of electric current. Metals such as copper and gold are good conductors, allowing for the rapid flow of electrons. Materials such as glass and Teflon, with structures that impede electron flow, are poor conductors. The atoms of metals have a structure allowing their electrons to behave as if they were free, or not bound to the atom.

The work by the Princeton team is part of an ongoing inquiry into materials called topological insulators -- substances that act as insulators in their interior while permitting the movement of charges on their boundary. In a phenomenon known as the quantum Hall effect, this behavior occurs when there is a perpendicular magnetic field applied to the material. And, in work conducted internationally by several researchers -- including a group led by Princeton physics professor Zahid Hasan -- a new type of topological insulator has been uncovered in which this behavior occurs even when there is no magnetic field present.

The crystals for the work were grown in the laboratory of Robert Cava, the Russell Wellman Moore Professor of Chemistry at Princeton.

The antimony crystal used in the experiment led by Yazdani is a metal but shares the unusual surface electron characteristics with related insulating compounds.

Because the electrons are able to move freely on the surface of the experimental material regardless of the shape of that surface, the material has a "topological surface state," Yazdani said. Topology is a major area of mathematics concerned with spatial properties that are preserved despite the deformation, like stretching, of objects. In that regard, a doughnut and a coffee cup can be viewed as topologically the same because they both are essentially areas with holes in the middle.

With lab instruments, the team was able to measure how long electrons are staying in a region of the material and how many of them flow through to other areas. The results showed a surprising efficiency by which surface electrons on antimony go through barriers that typically stop other surface electrons on the surface of most conducting materials, such as copper.

Authors on the paper include: Yazdani; postdoctoral fellows Jungpil Seo and Haim Beidenkopf ; graduate student Pedram Roushan; and, along with Cava, his former postdoctoral fellow Yew San Hor, who is now at the Missouri University of Science and Technology.

Yazdani's team worked in the specially designed Princeton Nanoscale Microscopy Laboratory, where highly accurate measurements at the atomic scale are possible because sounds and vibrations, through a multitude of technologies, are kept to a minimum. They used a powerful scanning tunneling microscope to view electrons on the surface of the antimony sample.

In such a microscope, an image is produced by pointing a finely focused electron beam, as in a TV set, across the studied sample. Researchers gently scan the microcope's single-atom sharp metal tip just above the surface of the material being studied. By monitoring the quantum "tunneling" of flowing from the needle into the sample, the instrument can produce precise images of atoms, as well as the flow of electron waves.

The experiment, Cava said, "shows for the first time that the theoretically predicted immunity of topological surface states to death at the hands of the ever-present defects in the atomic arrangements on crystal surfaces is really true."

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Jarek
not rated yet Jul 14, 2010
This dodging is probably similar effect like in the 'fractal patterns': http://physicswor...ws/41659
We always believed that naturally used 'locally maximizing entropy random walk' (all outgoing edges are equally probable) is the fundamental one - it leads to Brownian motion in continuous limit: good enough approximation for diffusion in fluids - but has nothing to do with QM.
Recently it occurs that we can do it better: use the real Maximum Entropy Random Walk - it says exactly what was needed: that on thermodynamical level (when we cannot trace the evolution, we use maximizing entropy ensemble among possible scenarios) we should assume 'wavefunction collapse' to the local lowest energy state precisely like in QM.

And so this random walk has strong localization properties like QM (Anderson etc) - 'dodging the cliff-like obstacles'
http://link.aps.o...2.160602
SteveL
not rated yet Jul 15, 2010
"For most metals, electrons in the interior carry most of the electrical current, with the electrons at the surface being only weakly mobile."

This is the opposite from what I was taught in school; that electrons travel over the surface of the metal. This is also counter to what I see out in the field. Any time higher currents are required multi-stranded or higher stranded wires are specified for the same wire gauge. Granted, this is for AC circuits. I am uncertain if DC would experience the same surface current effect.
KBK
not rated yet Jul 15, 2010
Antimony?

Very important in Alchemical works. One of the fundamental materials.

Why ignore Alchemy? 6,000 years later, after a lousy ~350 years of science (ie, simplistic left brained objectivism), it seems that the usual thing has taken place. As Arthur C Clarke said, "any sufficiently advanced science will appear as magic."

When it comes to alchemy, the problem is in the psychology of the person reviewing the information. Also understand that alchemy goes in to areas that are 'off the scale' more psychologically complex (with regard to what it reveals as possibilities in reality to the human mind) than one would imagine. The mind must be prepared for what is to be revealed.

Like any endeavor that approaches human 'limits' -- Man is reflected and changed in the expression of his ultimate reach.

In alchemy the researcher must also be in a state of perfection, in order to 'get there'. The mind is the limit-not alchemy. It is a maximal endeavor, therefore-exceedingly challenging.
KBK
1 / 5 (1) Jul 15, 2010
To clarify a bit, David Radius Hudson showed that when alchemists create 'the white powder of gold', it is superconductive.

Well, well, well....it's creation or manufacture involves the use of...............ANTIMONY.

Once again, as in every other case, the alchemists were and are correct. It is science that is the slow child. Literally. Science is an offshoot, a child of Alchemy. Alchemy is the mother of all sciences.

Newton, BTW, it has been revealed, through his now finally published private papers (bought by a Japanese gentleman)- to be the last 'great' alchemist.

Yes, Newton was at the core and through and through, truly an alchemist. The highest level of science, in it's most developed form (where the person involved must be perfected as well), is Alchemy.

Science is missing the 'middle steps', therefore it cannot make the observational and intuitive leaps.

Therefore Alchemy must be foolishness, correct?

Not so fast.

As the article above has so abundantly illustrated.
Jarek
2.3 / 5 (3) Jul 15, 2010
VestaR, since I hate this 1000 characters limit, let's take this discussion back where you've copypasted it:
http://physicswor...ws/43203
SteveL
not rated yet Jul 16, 2010
.. I was taught in school; that electrons travel over the surface of the metal. ..Granted, this is for AC circuits. ..
Granted, but the depth of skin effect is ~ 4 cm for 60 Hz AC. Now we are talking about DC at few nanometers depth bellow surface.


~ 4 cm? Um, that wouldn't be a "surface" effect. How many molecules deep is a few nanometers so that we can see through them using this new microsopy technique?
Jigga
2.3 / 5 (3) Jul 16, 2010
~ 4 cm? Um, that wouldn't be a "surface" effect
It depends.. This is how megawatt power AC cable appears because of the skin effect.

http://thefraserd...able.jpg

Diameter of copper atom is about 0,12 nm, lattice constant in YBaCuO superconductor is about 2 nm.
frajo
2.3 / 5 (3) Jul 16, 2010
~ 4 cm? Um, that wouldn't be a "surface" effect
It depends.. This is how megawatt power AC cable appears because of the skin effect.
http://thefraserd...able.jpg
The cable in your image has an outer diameter of 1.108 inch or 2.81 cm. This cable cannot have a skin effect of 4 cm.
Diameter of copper atom is about 0,12 nm, lattice constant in YBaCuO superconductor is about 2 nm.
What's that to do with a "skin effect" of 4 cm depth?
Are you paid by your customers per word, no matter how meaningless?
Jigga
2.3 / 5 (3) Jul 16, 2010
What's that to do with a "skin effect" of 4 cm depth?
Well, nothing. Ask SteveL - Jul 15, 2010 why he putted the sentence bellow, not me.

I was taught in school; that electrons travel over the surface of the metal. ..Granted, this is for AC circuits
I'm just explaining his misunderstanding. If you're not capable to follow discussion logics, don't interrupt it.
Paradox
3 / 5 (2) Jul 18, 2010
Granted, but the depth of skin effect is ~ 4 cm for 60 Hz AC. Now we are talking about DC at few nanometers depth bellow surface.


What?, explain then how you would get a 4cm skin effect on a #12 AWG wire at 60Hz....
on my screen, #12 is about the size of this "o".
Jigga
2.3 / 5 (3) Jul 18, 2010
You cannot get skin effect under such circumstances. Just forget the skin effect here at all - for topological insulators the conductive surface is based on different mechanism.
KBK
1 / 5 (2) Jul 25, 2010
Skin effect is based on delta.

The only thing that explains 'skin effect' after that observation is the interactives of torsionally spun vector interactives.

So the model subsequently becomes oscillating 2-d fields of infinite size in resonant interaction so the nearly perfectly balanced 'particle' is created with the slight unidirectional aspect that provides for stability and the unidirectional aspect of space-time. Not quite 100% in balance as this sheet like oscillating aspect is the leftover from the big bang, and they are actually curved out from that point but pass through one another and we see reality along the edge of it as if we are in 2-d land.

Our 'reality' is time based as it is created across the interactive points. Thus our quanta is created but we actually bridge across both..and all the other speculated aspects of reality (spooky action, psychic phenomena, other dimensions and realities, etc) are henceforth fully fleshed out.

One simple model - 100% functional.