Tag Archives: superconductors

Seaweed supercapacitors

I like munching on seaweed from time to time but it seems that seaweed may be more than just a foodstuff according to an April 5, 2017 news item on Nanowerk,

Seaweed, the edible algae with a long history in some Asian cuisines, and which has also become part of the Western foodie culture, could turn out to be an essential ingredient in another trend: the development of more sustainable ways to power our devices. Researchers have made a seaweed-derived material to help boost the performance of superconductors, lithium-ion batteries and fuel cells.

The team will present the work today [April 5, 2017] at the 253rd National Meeting & Exposition of the American Chemical Society (ACS). ACS, the world’s largest scientific society, is holding the meeting here through Thursday. It features more than 14,000 presentations on a wide range of science topics.

An April 5, 2017 American Chemical Society news release on EurekAlert), which originated the news item, gives more details about the presentation,

“Carbon-based materials are the most versatile materials used in the field of energy storage and conversion,” Dongjiang Yang, Ph.D., says. “We wanted to produce carbon-based materials via a really ‘green’ pathway. Given the renewability of seaweed, we chose seaweed extract as a precursor and template to synthesize hierarchical porous carbon materials.” He explains that the project opens a new way to use earth-abundant materials to develop future high-performance, multifunctional carbon nanomaterials for energy storage and catalysis on a large scale.

Traditional carbon materials, such as graphite, have been essential to creating the current energy landscape. But to make the leap to the next generation of lithium-ion batteries and other storage devices, an even better material is needed, preferably one that can be sustainably sourced, Yang says.

With these factors in mind, Yang, who is currently at Qingdao University (China), turned to the ocean. Seaweed is an abundant algae that grows easily in salt water. While Yang was at Griffith University in Australia, he worked with colleagues at Qingdao University and at Los Alamos National Laboratory in the U.S. to make porous carbon nanofibers from seaweed extract. Chelating, or binding, metal ions such as cobalt to the alginate molecules resulted in nanofibers with an “egg-box” structure, with alginate units enveloping the metal ions. This architecture is key to the material’s stability and controllable synthesis, Yang says.

Testing showed that the seaweed-derived material had a large reversible capacity of 625 milliampere hours per gram (mAhg-1), which is considerably more than the 372 mAhg-1 capacity of traditional graphite anodes for lithium-ion batteries. This could help double the range of electric cars if the cathode material is of equal quality. The egg-box fibers also performed as well as commercial platinum-based catalysts used in fuel-cell technologies and with much better long-term stability. They also showed high capacitance as a superconductor material at 197 Farads per gram, which could be applied in zinc-air batteries and supercapacitors. The researchers published their initial results in ACS Central Science in 2015 and have since developed the materials further.

For example, building on the same egg-box structure, the researchers say they have suppressed defects in seaweed-based, lithium-ion battery cathodes that can block the movement of lithium ions and hinder battery performance. And recently, they have developed an approach using red algae-derived carrageenan and iron to make a porous sulfur-doped carbon aerogel with an ultra-high surface area. The structure could be a good candidate to use in lithium-sulfur batteries and supercapacitors.

More work is needed to commercialize the seaweed-based materials, however. Yang says currently more than 20,000 tons of alginate precursor can be extracted from seaweed per year for industrial use. But much more will be required to scale up production.

Here’s an image representing the research,

Scientists have created porous ‘egg-box’ structured nanofibers using seaweed extract. Credit: American Chemical Society

I’m not sure that looks like an egg-box but I’ll take their word for it.

Nanodevices and quantum entanglement

A May 30, 2016 news item on phys.org introduces a scientist with an intriguing approach to quantum computing,

Creating quantum computers which some people believe will be the next generation of computers, with the ability to outperform machines based on conventional technology—depends upon harnessing the principles of quantum mechanics, or the physics that governs the behavior of particles at the subatomic scale. Entanglement—a concept that Albert Einstein once called “spooky action at a distance”—is integral to quantum computing, as it allows two physically separated particles to store and exchange information.

Stevan Nadj-Perge, assistant professor of applied physics and materials science, is interested in creating a device that could harness the power of entangled particles within a usable technology. However, one barrier to the development of quantum computing is decoherence, or the tendency of outside noise to destroy the quantum properties of a quantum computing device and ruin its ability to store information.

Nadj-Perge, who is originally from Serbia, received his undergraduate degree from Belgrade University and his PhD from Delft University of Technology in the Netherlands. He received a Marie Curie Fellowship in 2011, and joined the Caltech Division of Engineering and Applied Science in January after completing postdoctoral appointments at Princeton and Delft.

He recently talked with us about how his experimental work aims to resolve the problem of decoherence.

A May 27, 2016 California Institute of Technology (CalTech) news release by Jessica Stoller-Conrad, which originated the news item, proceeds with a question and answer format,

What is the overall goal of your research?

A large part of my research is focused on finding ways to store and process quantum information. Typically, if you have a quantum system, it loses its coherent properties—and therefore, its ability to store quantum information—very quickly. Quantum information is very fragile and even the smallest amount of external noise messes up quantum states. This is true for all quantum systems. There are various schemes that tackle this problem and postpone decoherence, but the one that I’m most interested in involves Majorana fermions. These particles were proposed to exist in nature almost eighty years ago but interestingly were never found.

Relatively recently theorists figured out how to engineer these particles in the lab. It turns out that, under certain conditions, when you combine certain materials and apply high magnetic fields at very cold temperatures, electrons will form a state that looks exactly as you would expect from Majorana fermions. Furthermore, such engineered states allow you to store quantum information in a way that postpones decoherence.

How exactly is quantum information stored using these Majorana fermions?

The fascinating property of these particles is that they always come in pairs. If you can store information in a pair of Majorana fermions it will be protected against all of the usual environmental noise that affects quantum states of individual objects. The information is protected because it is not stored in a single particle but in the pair itself. My lab is developing ways to engineer nanodevices which host Majorana fermions. Hopefully one day our devices will find applications in quantum computing.

Why did you want to come to Caltech to do this work?

The concept of engineered Majorana fermions and topological protection was, to a large degree, conceived here at Caltech by Alexei Kiteav [Ronald and Maxine Linde Professor of Theoretical Physics and Mathematics] who is in the physics department. A couple of physicists here at Caltech, Gil Refeal [professor of theoretical physics and executive officer of physics] and Jason Alicea [professor of theoretical physics], are doing theoretical work that is very relevant for my field.

Do you have any collaborations planned here?

Nothing formal, but I’ve been talking a lot with Gil and Jason. A student of mine also uses resources in the lab of Harry Atwater [Howard Hughes Professor of Applied Physics and Materials Science and director of the Joint Center for Artificial Photosynthesis], who has experience with materials that are potentially useful for our research.

How does that project relate to your lab’s work?

There are two-dimensional, or 2-D, materials that are basically very thin sheets of atoms. Graphene [emphasis mine]—a single layer of carbon atoms—is one example, but you can create single layer sheets of atoms with many materials. Harry Atwater’s group is working on solar cells made of a 2-D material. We are thinking of using the same materials and combining them with superconductors—materials that can conduct electricity without releasing heat, sound, or any other form of energy—in order to produce Majorana fermions.

How do you do that?

There are several proposed ways of using 2-D materials to create Majorana fermions. The majority of these materials have a strong spin-orbit coupling—an interaction of a particle’s spin with its motion—which is one of the key ingredients for creating Majoranas. Also some of the 2-D materials can become superconductors at low temperatures. One of the ideas that we are seriously considering is using a 2-D material as a substrate on which we could build atomic chains that will host Majorana fermions.

What got you interested in science when you were young?

I don’t come from a family of scientists; my father is an engineer and my mother is an administrative worker. But my father first got me interested in science. As an engineer, he was always solving something and he brought home some of the problems he was working. I worked with him and picked it up at an early age.

How are you adjusting to life in California?

Well, I like being outdoors, and here we have the mountains and the beach and it’s really amazing. The weather here is so much better than the other places I’ve lived. If you want to get the impression of what the weather in the Netherlands is like, you just replace the number of sunny days here with the number of rainy days there.

I wish Stevan Nadj-Perge good luck!

Soccer balls with no resistance (superconductivity)

Known as a fullerene (also buckminsterfullerene, buckyballs, and/or C60), the soccer ball in question is helping scientists to better understand how to develop materials that are superconductive at room temperature. A Feb. 9, 2016 news item on Nanotechnology Now describes the latest in ‘soccer ball’ research,

Superconductors have long been confined to niche applications, due to the fact that the highest temperature at which even the best of these materials becomes resistance-free is minus 70 degrees Celsius. Nowadays they are mainly used in magnets for nuclear magnetic resonance tomographs, fusion devices and particle accelerators. Physicists from the Max Planck Institute for the Structure and Dynamics of Matter at the Center for Free-Electron Laser Science (CFEL) in Hamburg shone laser pulses at a material made up from potassium atoms and carbon atoms arranged in bucky ball structures. For a small fraction of a second, they found it to become superconducting at more than 100 degrees Kelvin – around minus 170 degrees Celsius. A similar effect was already discovered in 2013 by scientists of the same group in a different material, a ceramic oxide belonging to the family of so-called “cuprates”. As fullerenes have a relatively simple chemical structure, the researchers hope to be able to gain a better understanding of the phenomenon of light-induced superconductivity at high temperatures through their new experiments. Such insights could help in the development of a material which conducts electricity at room temperature without losses, and without optical excitation.

A Feb. 8, 2016 Max Planck Institute press release (also on EurekAlert but dated Feb. 9, 2016), which originated the news item, expands on the theme of superconductivity at room temperature,

Andrea Cavalleri, Director at the Max Planck Institute for the Structure and Dynamics of Matter, and his colleagues aim at paving the way for the development of materials that lose their electrical resistance at room temperature. Their observation that fullerenes, when excited with laser pulses, can become superconductive at minus 170 degrees Celsius, takes them a step closer to achieving this goal. This discovery could contribute to establishing a more comprehensive understanding of light-induced superconductivity, because it is easier to formulate a theoretical explanation for fullerenes than for cuprates. A complete explanation of this effect could, in turn, help the scientists to gain a better understanding of the phenomenon of high-temperature superconductivity and provide a recipe for an artificial superconductor that conducts electricity without resistance losses at room temperature.

In 2013, researchers from Cavalleri’s group demostrated that under certain conditions it may be possible for a material to conduct electricity at room temperature without resistance loss. A ceramic oxide belonging to the family of cuprates was shown to become superconductive without any cooling for a few trillionths of a second when the scientists excited it using an infrared laser pulse. One year later, the Hamburg-based scientists presented a possible explanation for this effect.

They observed that, following excitation with the flash of light, the atoms in the crystal lattice change position. This shift in position persists as does the superconducting state of the material. Broadly speaking, the light-induced change in the structure clears the way for the electrons so that they can move through the ceramic without losses. However, the explanation is very dependent on the highly specific crystalline structure of cuprates. As the process was understood at the time, it could have involved a phenomenon that only arises in this kind of materials.

The researchers have included in the press release an image illustrating the latest work being described in the press release excerpt which follows this,

Intense laser flashes remove the electrical resistance of a crystal layer of the alkali fulleride K3C60, a football-like molecule containing 60 carbon atoms. This is observed at temperatures at least as high as minus 170 degrees Celsius. © J.M. Harms/MPI for the Structure and Dynamics of Matter

Intense laser flashes remove the electrical resistance of a crystal layer of the alkali fulleride K3C60, a football-like molecule containing 60 carbon atoms. This is observed at temperatures at least as high as minus 170 degrees Celsius.
© J.M. Harms/MPI for the Structure and Dynamics of Matter

The press release goes on to provide some technical details about the most recent research,

The team headed by Cavalleri therefore asked themselves whether light could also break the electrical resistance of more traditional superconductors, the physics of which is better understood. The researchers from the Max Planck Institute for the Structure and Dynamics of Matter, among which Daniele Nicoletti and Matteo Mitrano, have now hit the jackpot using a substance that is very different to cuprates: the fulleride K3C60, a metal composed of so-called Buckminster fullerenes. These hollow molecules consist of 60 carbon atoms which bond in the shape of a football: a sphere comprising pentagons and hexagons. With the help of intercalated positively charged potassium ions, which work like a kind of cement, the negatively charged fullerenes stick to each other to form a solid. This so-called alkali fulleride is a metal which becomes superconductive below a critical temperature of around minus 250 degrees Celsius.

The researchers then irradiated the alkali fulleride with infrared light pulses of just a few billionths of a microsecond and repeated their experiment for a range of temperatures between the critical temperature and room temperature. They set the frequency of the light source so that it excited the fullerenes to produce vibrations. This causes the carbon atoms to oscillate in such a way that the pentagons in the football expand and contract. It was hoped that this change in the structure could generate transient superconductivity at high temperatures in a similar way to the process in cuprates.

To test this, the scientists irradiated the sample with a second light pulse at the same time as the infrared pulse, albeit at a frequency in the terahertz range. The strength at which this pulse is reflected indicates the conductivity of the material to the researchers, meaning how easily electrons move through the alkali fulleride. The result here was an extremely high conductivity. “We are pretty confident that we have induced superconductivity at temperatures at least as high as minus 170 degrees Celsius,” says Daniele Nicoletti. This means that the experiment in Hamburg presents one of the highest ever-observed critical temperatures outside of the material class of cuprates.

“We are now planning to carry out other experiments which should enable us to reach a more detailed understanding of the processes at work here,” says Nicoletti. What they would like to do next is analyze the crystal structure during excitation with the infrared light. As was previously the case with the cuprate, this should help to explain the phenomenon. The researchers would then like to irradiate the material with light pulses that last much longer. “Although this is technically very complicated, it could extend the lifetime of superconductivity, making it potentially relevant for applications,” concludes Nicoletti.

Here’s a link to and a citation for the paper,

Possible light-induced superconductivity in K3C60 at high temperature by M. Mitrano, A. Cantaluppi, D. Nicoletti, S. Kaiser, A. Perucchi, S. Lupi, P. Di Pietro, D. Pontiroli, M. Riccò, S. R. Clark, D. Jaksch, & A. Cavalleri. Nature (2016) doi:10.1038/nature16522 Published online 08 February 2016

This paper is behind a paywall.