Tag Archives: superconductor

Scientists combine a semiconductor and superconductor for the first time

The monolayer of semiconducting material is sandwiched between two insulating layers with a superconducting contact extending through the upper one. Credit: Mehdi Ramezani, Swiss Nanoscience Institute, University of Basel.

Physicists in Switzerland managed to arrange an unholy matrimony between an ultrathin semiconductor and an ultra-chilled superconductor. The resulting device allows for peculiar physical phenomena to form that may prove useful in manufacturing novel electronic and optical machines such as quantum computers.

Exotic physics for the exotic applications of the future

Semiconductors have recently made headlines due to shortages that are threatening to disrupt the global supply of consumer electronics. Smartphones, TVs, automobiles, and virtually anything that is tech (which is virtually anything ‘smart’ nowadays) all rely on semiconductors, which are materials that can switch current on and off. These allow processors to perform boolean logic and solar panels to harvest electricity from photons.

Superconductors on the other hand are like frictionless highways for electrons, being able to carry the charged particles with zero electrical resistance. The most common superconductors typically have to be cooled down with liquid nitrogen close to -250°C (-480°F) for them to conduct electricity with no resistance. In this state, the conductor is composed of a rigid lattice of positive ions drowned in a sea of electrons.

A normal conductor has electrical resistance because electrons moving through the lattice also bump into it, slowing down in the process. This motion also causes atoms to vibrate, which is why electrical resistivity also leads to energy loss as heat.

On the other hand, in a superconductor, the lattice is so rigid due to the low temperature that mechanical sound waves (phonons) ripple through it — and electrons ride the wave along with them. What’s more, electrons in a superconductor form bonds called ‘Cooper pairs’ which flow through the material like a fluid. But if the temperature rises, the Cooper pairs break apart and the superconductive state dissolves.

“In a superconductor, the electrons arrange themselves into pairs, like partners in a dance – with weird and wonderful consequences, such as the flow of the electrical current without a resistance,” said Dr. Andreas Baumgartner, a researcher at the Swiss Nanoscience Institute and the Department of Physics of the University of Basel and lead-author of the new study.

“In the semiconductor molybdenum disulfide, on the other hand, the electrons perform a completely different dance, a strange solo routine that also incorporates their magnetic moments. Now we would like to find out which new and exotic dances the electrons agree upon if we combine these materials.”

Baumgartner and colleagues embarked on their research looking to experiment with ultrathin semiconductors, which are materials no thicker than a single molecule. These monolayer semiconductors should theoretically be able to exhibit unique and appealing characteristics such as the use of electric fields to influence the magnetic moments of electrons. Additionally, monolayer semiconductors may exhibit wacky quantum mechanical phenomena that may prove useful in developing the next generation of quantum computers.

By stacking multiple such monolayers of semiconductors it is possible to make new synthetic materials known as van der Waals heterostructures with unique interlayer coupling and optoelectronic properties.

The researchers went a step further and experimented by adding superconducting contacts to a monolayer of the semiconductor molybdenum disulfide. No other research group devised a van der Waals heterostructure with a superconductor before.

To protect the fragile atom-thick semiconductor, the researchers sandwiched the material between two thin layers of boron nitride, through which they had previously etched the contacts vertically using electron-beam lithography and ion etching. A thin layer of molybdenum rhenium (the contact superconductor) was then carefully added. In this configuration, the material retains its superconducting properties even in the presence of strong magnetic fields.

The researchers found evidence of strong coupling between the semiconductor layer and the superconductor, which were chilled to just above absolute zero (-273.15°C).

“Strong coupling is a key element in the new and exciting physical phenomena that we expect to see in such van der Waals heterostructures, but were never able to demonstrate,” says Mehdi Ramezani, lead author of the study.

“And, of course, we always hope for new applications in electronics and quantum technology,” says Baumgartner. “In principle, the vertical contacts we’ve developed for the semiconductor layers can be applied to a large number of semiconductors. Our measurements show that these hybrid monolayer semiconductor components are indeed possible –perhaps even with other, more exotic contact materials that would pave the way for further insights,” he adds.

Now that this prototype was deemed feasible, the researchers in Switzerland plan on experimenting with other types of semiconductors and different stacking configurations.

Graphite powder

Hints of superconductivity at room temperature might hold far-reaching consequences

By doping graphite, researchers in Germany have reported that they found tantalizing hints of superconductivity at room-temperatures and far above, like water boiling point (100°C.). Superconductivity is a property which describes zero resistance electrical conductivity, however this property has only been observed at temperatures lower than -100°C.

Graphite powder

Graphite powder.

Graphite has been found to exhibit superconductivity in the past, when doped with elements that provide additional free electrons. For instance, calcium doped graphite superconducts at up to 11.5 kelvin (about -260 °C), while 60 kelvin could be reached if enough free electrons were made available.

With this in mind Pablo Esquinazi and his colleagues at the University of Leipzig sought to bend the superconductivity limit. Their first attempts rendered some very interesting results with an artificial type of bulk graphite known as pyrolytic graphite, which they managed to superconduct at 100 kelvin. They found that electrons concentrate in high density at the interfaces between neighbouring thin segments of graphite. Graphite an allotrope and most stable form of carbon, is made up of layers of carbon atoms arranged in hexagonal lattices, and is considered a very good electrical conductor.

For their next attempt, the researchers took a hit a carbon powder, which they mixed with water. Thus, they placed 100 milligrams of pure graphite powder made up of flakes a few hundredths of a millimetre long and tens of nanometres thick into 20 millilitres of distilled water. After mixing, the powder was filtered and dried. When the sample was magnetized, the scientists observed that the sample continued to remain magnetized even after the magnetic field was removed. This is either a characteristic of superconductivity or ordinary ferromagnetism.

To rule out the latter, the scientists probed how the magnetization varied with the strength of the applied field and with temperature. Their results were on par with the first high-temperature oxide superconductors, discovered in the 1980s.

Now, no actual zero resistance electric conductivity was proven, nor did the researchers show that the magnetic fields are absent from the interior of the flakes — a fundamental characteristic of superconductors. However, what’s interesting though is that this apparent superconductivity wasn’t lost at very high temperatures. The team reports that the superconducting state remained at temperatures up to about 400 kelvin, or around 130 °C, well above the boiling point of water. Even Esquinazi admits that the claim “sounds like science fiction”, nevertheless their findings are extremely interesting and later scrutiny of the results should prove to be even more interesting. If indeed doped graphite powder is found to superconduct, than the ramifications of this scientific find would be enormous.

The report was published in the journal Advanced Materials.

source: Nature

A graphic representation of the flux tubes inside the superconductive material coated wafer. (c) Tel Aviv University

Watch Quantum Levitation in action [AMAZING!]

What you just saw in the video above is a perfect demonstration of the quantum levitation effect, through a fairly simple set-up made by Tel Aviv University scientists, comprised of a track and a semiconductor.

A graphic representation of the flux tubes inside the superconductive material coated wafer. (c) Tel Aviv University

A graphic representation of the flux tubes inside the superconductive material coated wafer. (c) Tel Aviv University

The quantum levitation is actually a perfect demonstration of the Meissner effect, which describes the expulsion of a magnetic field from a superconductor during its transition to the superconducting state. Because of this the superconductor will expel all the magnetic field from inside, however since the superconductive material is very thin, magnetic fields do actually penetrate, but at discrete levels called flux tubes, hence the quantum physics implications. Because of these tubes, superconductive is eliminated in grain bounderies, and thus spatially locks the material.

For this particular set-up, the Tel Aviv scientists used a ceramic material called yttrium barium copper oxide (YBa2Cu3O7-x ) to a ~1µm thick layer on a single crystal sapphire wafer. To reach its superconductive state (no resistivity and no energy loss), the scientists cooled the material to  -185ºC. Experiments and demonstrations of the Meissner effect have been made numerous times in the past decades, however this particular demo shows how quantum gravitation can be achieved fairly easily, and hints of a quicker pace set to finally develop working applications that harness the effect.


The 100 Mb Ion 316 semiconductor sequencing chip released in July 2011

New DNA sequencing device could decode your genome for just $1000

The inventor Jonathan Rothberg with a semiconductor chip used in the Ion Torrent machine. (c) Christopher Capozziello , NY Times

The inventor Jonathan Rothberg with a semiconductor chip used in the Ion Torrent machine. (c) Christopher Capozziello , NY Times

News of a low-cost semiconductor-based gene sequencing machine has been reported this Wednesday in the journal Nature, by a team led by Jonathan Rothberg. The astonishing advancement might lead to a age of personal human genome sequence, where people will be able to decipher their own DNA for as low as $1000.

The human genome was first mapped in 2001 and cost roughly $1 billion to do. Now, ten years and other tens of billions of dollars later important advancements have led to further detailed research, like the sequencing of a complete neanderthal genome, as well as optimization of the process and technology employed so it might become cheaper and faster.

Inventor, Jonathan Rothberg of Ion Torrent Systems in Guilford, Conn., is one of several pursuing the goal of a $1,000 human genome, which he said he could reach by 2013 because his machine is rapidly being improved. To test their genome device, they chose to map the one of Intel’s co-founder, Gordon Moore, the man behind the famed “Moore’s Law” prediction of exponentially growing computer power.

“Gordon Moore worked out all the tricks that gave us modern semiconductors, so he should be the first person to be sequenced on a semiconductor,” Dr. Rothberg said.

The 100 Mb Ion 316 semiconductor sequencing chip released in July 2011

The 100 Mb Ion 316 semiconductor sequencing chip released in July 2011. (c) Ion Torrent

The technology employs semiconductor chip to sense DNA or genetic material by detecting a voltage change, instead of light. This eliminates the use of highly expensive equipment that would’ve been required otherwise. Using this tech, the evolution of which is compared by its researchers with that of the digital camera, scientists have been able to scan three bacterial strains and one human genome.

“When it [digital photography] first started out, the resolution was not good and the pictures were not as good as on film. But the technology improved, which made it more accessible and now more people can enjoy photography and become better photographers,” Dr. Maneesh Jain, vice president of marketing and business development at Ion Torrent said.

The human genome is that of Dr. Moore, as you’ve been given to find out earlier, and as for the bacterial strains, the first two genomes of the deadly E. coli bacteria that swept Europe in the spring were decoded on the company’s machines. The whole decoding process takes less than two hours to complete!

Applications, of course, are numerous especially for the common users. At $1000, a genome sequence might become as common as a medical check in the very close future. You’d then be confronted with your very own mapped genome, which when interpreted can describe various medical condition predispositions, leading to the so-called personalized medicine, which seeks to avoid trial-and-error by using genetic data found during a scan to better pair treatments with diseases.

Tell me what your genes are, so I can tell you who you are

Don’t expect everything you get back to be extremely accurate, though. Dr. Moore’s genome has a genetic variant that denotes a “56 percent chance of brown eyes,” one that indicates a “typical amount of freckling” and another that confers “moderately higher odds of smelling asparagus in one’s urine,” Dr. Rothberg and his colleagues reported. Also, Dr. Moore’s genome has two strains that seems to indicated towards an “increased risk of mental retardation” — which was obviously never the case.

Genetic hazards, however, come at a much lower stake than those caught up during one’s lifetime.

“Most of what genetics tell us is that there are a lot of fairly common variants that have a modest degree of risk for diseases,” Dr. Peter Gregersen, director of the Robert S. Boas Center for Genomics and Human Genetics at the Feinstein Institute for Medical Research in Manhasset, N.Y said. “This is important from a scientific point of view, but the data itself is not actionable.

“The risk of disease associated with high blood pressure, smoking and high cholesterol is far greater than most of the genetic risks coming out of whole genome scanning,” Gregersen added. For example, if your genome scan identified a mutation that put you at risk for macular degeneration, a leading cause of blindness, “you may see an ophthalmologist, and there are forms that are treatable, but knowing your genetics won’t impact this much,” he said.

More time, research and money is needed for a more useful information to be outputted by a genome sequencing machine, as the human DNA is decoded to a more precise degree. We might be headed towards Gattaca hell, a utopian/dystopian climate, depends on how you decide to favor it, where everything will be known about you before you’re even born – how you’ll look when you’re 25, how smart can you become, where you’d be best fitted for work, whether there’s a chance you’ll condone in criminal behavior, etc. It’s all in the genes my momma used to tell me…

A Cambridge University video with superconductors and how amazingly useful they can be

Superconductivity occurs when the natural electrical resistance is exactly 0; it occurs in certain materials at very low temperatures. According to the Cambridge University youtube channel:

The first in a new range of powerful superconductors which could revolutionise the production of machines like hospital MRI scanners and protect the national grid have been developed by engineers at the University of Cambridge. Professor David Cardwell explains what superconductors are, why we need them, and how he and his team have devised techniques to make them more powerful than ever before.