Tag Archives: Heisenberg’s Uncertainty Principle

Carbyne stretches from theory to reality and reveals its conundrum-type self

Rice University (Texas, US) scientists have taken a rather difficult material, carbyne, and twisted it to reveal new properties according to a July 21, 2014 news item on ScienceDaily,

Applying just the right amount of tension to a chain of carbon atoms can turn it from a metallic conductor to an insulator, according to Rice University scientists.

Stretching the material known as carbyne — a hard-to-make, one-dimensional chain of carbon atoms — by just 3 percent can begin to change its properties in ways that engineers might find useful for mechanically activated nanoscale electronics and optics.

A July 21, 2014 Rice University news release (also on EurekAlert), which originated the news item, describes carbyne and some of the difficulties the scientists addressed in their research on the material,

Until recently, carbyne has existed mostly in theory, though experimentalists have made some headway in creating small samples of the finicky material. The carbon chain would theoretically be the strongest material ever, if only someone could make it reliably.

The first-principle calculations by Yakobson and his co-authors, Rice postdoctoral researcher Vasilii Artyukhov and graduate student Mingjie Liu, show that stretching carbon chains activates the transition from conductor to insulator by widening the material’s band gap. Band gaps, which free electrons must overcome to complete a circuit, give materials the semiconducting properties that make modern electronics possible.

In their previous work on carbyne, the researchers believed they saw hints of the transition, but they had to dig deeper to find that stretching would effectively turn the material into a switch.

Each carbon atom has four electrons available to form covalent bonds. In their relaxed state, the atoms in a carbyne chain would be more or less evenly spaced, with two bonds between them. But the atoms are never static, due to natural quantum uncertainty, which Yakobson said keeps them from slipping into a less-stable Peierls distortion.

“Peierls said one-dimensional metals are unstable and must become semiconductors or insulators,” Yakobson said. “But it’s not that simple, because there are two driving factors.”

One, the Peierls distortion, “wants to open the gap that makes it a semiconductor.” The other, called zero-point vibration (ZPV), “wants to maintain uniformity and the metal state.”

Yakobson explained that ZPV is a manifestation of quantum uncertainty, which says atoms are always in motion. “It’s more a blur than a vibration,” he said. “We can say carbyne represents the uncertainty principle in action, because when it’s relaxed, the bonds are constantly confused between 2-2 and 1-3, to the point where they average out and the chain remains metallic.”

But stretching the chain shifts the balance toward alternating long and short (1-3) bonds. That progressively opens a band gap beginning at about 3 percent tension, according to the computations. The Rice team created a phase diagram to illustrate the relationship of the band gap to strain and temperature.

How carbyne is attached to electrodes also matters, Artyukhov said. “Different bond connectivity patterns can affect the metallic/dielectric state balance and shift the transition point, potentially to where it may not be accessible anymore,” he said. “So one has to be extremely careful about making the contacts.”

“Carbyne’s structure is a conundrum,” he said. “Until this paper, everybody was convinced it was single-triple, with a long bond then a short bond, caused by Peierls instability.” He said the realization that quantum vibrations may quench Peierls, together with the team’s earlier finding that tension can increase the band gap and make carbyne more insulating, prompted the new study.

“Other researchers considered the role of ZPV in Peierls-active systems, even carbyne itself, before we did,” Artyukhov said. “However, in all previous studies only two possible answers were being considered: either ‘carbyne is semiconducting’ or ‘carbyne is metallic,’ and the conclusion, whichever one, was viewed as sort of a timeless mathematical truth, a static ‘ultimate verdict.’ What we realized here is that you can use tension to dynamically go from one regime to the other, which makes it useful on a completely different level.”

Yakobson noted the findings should encourage more research into the formation of stable carbyne chains and may apply equally to other one-dimensional chains subject to Peierls distortions, including conducting polymers and charge/spin density-wave materials.

According to the news release the research was funded by the U.S. Air Force Office of Scientific Research, the Office of Naval Research Multidisciplinary University Research Initiative, and the Robert Welch Foundation. (I can’t recall another instance of the air force and the navy funding the same research.) In any event, here’s a link to and a citation for the paper,

Mechanically Induced Metal–Insulator Transition in Carbyne by Vasilii I. Artyukhov, Mingjie Liu, and Boris I. Yakobson. Nano Lett., Article ASAP DOI: 10.1021/nl5017317 Publication Date (Web): July 3, 2014

Copyright © 2014 American Chemical Society

This paper is behind a paywall.

The researchers have provided an image to illustrate their work,

[downloaded from http://pubs.acs.org/doi/abs/10.1021/nl5017317]

[downloaded from http://pubs.acs.org/doi/abs/10.1021/nl5017317]

I’m not sure what the bird is doing in the image but it caught my fancy. There is another less whimsical illustration (you can see it in the  July 21, 2014 news item on ScienceDaily) and I believe the same caption can be used for the one I’ve chosen from the journal’s abstract page, “Carbyne chains of carbon atoms can be either metallic or semiconducting, according to first-principle calculations by scientists at Rice University. Stretching the chain dimerizes the atoms, opening a band gap between the pairs. Credit: Vasilii Artyukhov/Rice University.”

I last wrote about carbyne in an Oct. 9, 2013 posting where I noted that the material was unlikely to dethrone graphene as it didn’t appear to have properties useful in electronic applications. It seems the scientists have proved otherwise, at least in the laboratory.

With a song in your heart and multiplexed images in an atomic vapor

A specific piece of research has inspired a song with lyrics based on the text of a research paper and, weirdly, it works. You will have a song in your heart and on your lips and it’s all to do with storing images in an atomic vapor,

Hot, hot, hot, eh?

As for the research paper itself (Temporally multiplexed storage of images in a Gradient Echo Memory), it’s currently availab.e at arXiv.org or in Optics Express, Vol. 20, Issue 11, pp. 12350-12358 (2012) DOI: 10.1364/OE.20.012350(authors: Quentin Glorieux, Jeremy B. Clark, Alberto M. Marino, Zhifan Zhou, Paul D. Lett). The May 29, 2012 news item on Nanowerk offers some tantalizing tidbits about the work,

The storage of light-encoded messages on film and compact disks and as holograms is ubiquitous—grocery scanners, Netflix disks, credit-card images are just a few examples. And now light signals can be stored as patterns in a room-temperature vapor of atoms. Scientists at the Joint Quantum Institute [JQI] have stored not one but two letters of the alphabet in a tiny cell filled with rubidium (Rb) atoms which are tailored to absorb and later re-emit messages on demand. This is the first time two images have simultaneously been reliably stored in a non-solid medium and then played back.

In effect, this is the first stored and replayed atomic movie. Because the JQI researchers are able to store and replay two separate images, or “frames,” a few micro-seconds apart, the whole sequence can qualify as a feat of cinematography.

Here’s a little more detail about how this was done and some information about the implications,

Having stored one image (the letter N), the JQI physicists then stored a second image, the letter T, before reading both letters back in quick succession. The two “frames” of this movie, about a microsecond apart, were played back successfully every time, although typically only about 8 percent of the original light was redeemed, a percentage that will improve with practice. According to Paul Lett, one of the great challenges in storing images this way is to keep the atoms embodying the image from diffusing away. The longer the storage time (measured so far to be about 20 microseconds) the more diffusion occurs. The result is a fuzzy image.

Paul Lett plans to link up these new developments in storing images with his previous work on squeezed light. “Squeezing” light is one way to partially circumvent the Heisenberg uncertainty principle governing the ultimate measurement limitations. By allowing a poorer knowledge of a stream of light—say the timing of the light, its phase—one gain a sharper knowledge of a separate variable—in this case the light’s amplitude. This increased capability, at le ast for the one variable, allows higher precision in certain quantum measurements.

“The big thing here,” said Lett, “is that this allows us to do images and do pulses (instead of individual photons) and it can be matched (hopefully) to our squeezed light source, so that we can soon try to store “quantum images” and make essentially a random access memory for continuous variable quantum information. The thing that really attracted us to this method—aside from its being pretty well-matched to our source of squeezed light—is that the ANU [Australian National University] group was able to get 87% recovery efficiency from it – which is, I think, the best anyone has seen in any optical system, so it holds great promise for a quantum memory.”

I may never totally understand this work but at least I now have a song to sing and for anyone who wants more details, the May 27, 2012 news item on Nanowerk provides details and images, as well as, another opportunity to watch the song.  I did check out the video on YouTube and found that it’s by therockcookiebottom and is part of a project, Song A Day: 1000 Days and Counting that singer-songwriter, Jonathan Mann started in Jan. 2009. I imagine that means he  must be nearing the end. Thank you Jonathan for a very entertaining and educational song. He does offer memberships to support him and his song-a-day project and opportunities to hire him for any songwriting projects you may have.

Quantum realities and perceptions (part 3 of 3); call for economic analyses of nano in Europe; Don Eigler hypes nano

I’m not much inclined to discuss philosophy or the nature of reality  as I often find myself tangled up in my own words and ideas. Consequently, I don’t have any grand conclusions about quantum realities and perceptions other than to say that how we approach the nature of reality is a collective exercise. I don’t mean that we all agree to some particular version rather, we engage with each other in various and, at times competing, ‘conversations’ out of which emerges a complex worldview which is forever dynamic. A little bit like Heisenberg’s Uncertainty Principle. In a very simplified form, it is impossible to measure  both a particle’s position and its momentum  with any accuracy. The more information you have about one of these properties, the less you know about the other.  There is an addition to this principle called the Copenhagen Interpretation which suggests that you can know the past position and momentum of a particle but not the present position and momentum.

The discussion about nanotechnology is really part of the larger discussion of science and technology, which in turn, is contained in a discussion about the nature of reality, perception, and our relationships with each other and this planet. As for that dynamic conversation I mentioned earlier, it includes business people , activists, scientists, writers (fiction and nonfiction), pop culture purveyors (movies, etc.), government policy makers, the general public, and others. As well, individuals may be members of more than one of these groups.

It is possible to look into the past and determine world views for distinct regional areas but trying to determine a single over-arching worldview for the planet is not possible. It may exist but it is impossible for the observer to know it.