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Showing posts with label Electronics. Show all posts
Showing posts with label Electronics. Show all posts

Saturday, 26 June 2021

Rechargeable smartphones in 5 minutes? A new imaging technique is fast approaching us


The key to advancing lithium-ion battery technology requires a better understanding of the dynamic processes in functioning materials under realistic conditions. Imaging of lithium-ion dynamics during battery operation requires sophisticated synchrotron X-ray or electron microscopy techniques. 

However, these techniques lend themselves to high-throughput material screening. This limits rapid and rational materials improvements.

To study what’s happening inside a battery, the Cambridge team developed an optical microscopy technique called interferometric scattering microscopy to observe these processes at work. The technique help scientists determine the speed-limiting processes, which, if addressed, could enable the batteries in most smartphones and laptops to charge in as little as five minutes.

In addition, the technique could accelerate the development of next-generation batteries.

Using the technique, scientists observed the charge-discharge cycle of individual particles of lithium cobalt oxide. They did so by measuring the amount of scattered light.

They were able to see the LCO going through a series of phase transitions in the charge-discharge cycle. The phase boundaries within the LCO particles move and change as lithium ions go in and out.

Scientists found that the mechanism of the moving boundary is different depending on whether the battery is charging or discharging.

Dr. Akshay Rao from the Cavendish Laboratory, who led the research, said, “We found that there are different speed limits for lithium-ion batteries, depending on whether it’s charging or discharging. When charging, the speed depends on how fast the lithium ions can pass through active material particles. When discharging, the speed depends on how fast the ions are inserted at the edges. So if we can control these two mechanisms, it would enable lithium-ion batteries to charge much faster.”

“Given that lithium-ion batteries have been in use for decades, you’d think we know everything there is to know about them, but that’s not the case. This technique lets us see just how fast it might be able to go through a charge-discharge cycle. What we’re looking forward to is using the technique to study next-generation battery materials – we can use what we learned about LCO to develop new materials.”

Professor Clare Grey, from Cambridge’s Yusuf Hamied Department of Chemistry, who co-led the research, said, “The technique is a quite general way of looking at ion dynamics in solid-state materials so that you can use it on almost any type of battery material.”

“The high throughput nature of the methodology allows many particles to be sampled across the entire electrode and, moving forward, will enable further exploration of what happens when batteries fail and how to prevent it.”

“This lab-based technique we’ve developed offers a huge change in technology speed so that we can keep up with the fast-moving inner workings of a battery. The fact that we can see these phase boundaries changing in real time was really surprising. This technique could be an important piece of the puzzle in the development of next-generation batteries.”

Reference:

Alice J. Merryweather et al. ‘Operando optical tracking of single-particle ion dynamics in batteries.’ Nature (2021). DOI: 10.1038/s41586-021-03584-2

Tuesday, 22 June 2021

Physicists create platform to achieve ultra-strong photon-to-magnon coupling


A team of scientists from NUST MISIS and MIPT have developed and tested a new platform for realization of the ultra-strong photon-to-magnon coupling. The proposed system is on-chip and is based on thin-film hetero-structures with superconducting, ferromagnetic and insulating layers. This discovery solves a problem that has been on the agenda of research teams from different countries for the last 10 years, and opens new opportunities in implementing quantum technologies. The study was published in the highly ranked journal Science Advances.

The last decade has seen significant progress in the development of artificial quantum systems. Scientists are exploring different platforms, each with its own advantages and disadvantages. The next critical step for advancing quantum industry requires an efficient method of information exchange between platform hybrid systems that could benefit from distinct platforms. For example, hybrid systems based on collective spin excitations, or magnons, are being developed. In such systems, magnons must interact with photons, standing electromagnetic waves trapped in a resonator. The main limiting factor for developing such systems is the fundamentally weak interaction between photons and magnons. They are of different sizes, and follow different dispersion laws. This size difference of a hundred times or more considerably complicates the interaction.

Scientists from MIPT, together with their colleagues, managed to create a system with what is called the ultra-strong photon-to-magnon coupling.

Vasily Stolyarov, deputy head of the MIPT Laboratory of Topological Quantum Phenomena in Superconducting Systems, commented, "We created two subsystems. In one, being a sandwich from superconductor/insulator/superconductor thin films, photons are slowed down, their phase velocity is reduced. In another one, which is also a sandwich from superconductor/ ferromagnetic/ superconductor thin films, superconducting proximity at both interfaces enhances the collective spin eigen-frequencies. The ultra strong photon-to-magnon coupling is achieved thanks to the suppressed photon phase velocity in the electromagnetic subsystem."

Igor Golovchanskiy, leading researcher, senior researcher at the MIPT Laboratory of Topological Quantum Phenomena in Superconducting Systems, head of the NUST MISIS Laboratory of Cryogenic Electronic Systems, explained, "Photons interact very weakly with magnons. We managed to create a system in which these two types of excitations interact very strongly. With the help of superconductors, we have significantly reduced the electromagnetic resonator. This resulted in a hundred times reduction of the phase velocity of photons, and their interaction with magnons increased by several times."

This discovery will accelerate the implementation of hybrid quantum systems, as well as open up new possibilities in superconducting spintronics and magnonics.

Reference: 

Igor A. Golovchanskiy et al, Ultrastrong photon-to-magnon coupling in multilayered heterostructures involving superconducting coherence via ferromagnetic layers, Science Advances (2021). DOI: 10.1126/sciadv.abe8638


Friday, 11 June 2021

New Quantum Microscope Reveals Biological Detail Otherwise Impossible To See



In a major scientific leap, University of Queensland researchers have created a quantum microscope that can reveal biological structures that would otherwise be impossible to see.

This paves the way for applications in biotechnology, and could extend far beyond this into areas ranging from navigation to medical imaging.

The microscope is powered by the science of quantum entanglement, an effect Einstein described as “spooky interactions at a distance”.

Professor Warwick Bowen, from UQ’s Quantum Optics Lab and the ARC Centre of Excellence for Engineered Quantum Systems (EQUS), said it was the first entanglement-based sensor with performance beyond the best possible existing technology.

“This breakthrough will spark all sorts of new technologies – from better navigation systems to better MRI machines, you name it,” Professor Bowen said.

“Entanglement is thought to lie at the heart of a quantum revolution.

“We’ve finally demonstrated that sensors that use it can supersede existing, non-quantum technology.

“This is exciting – it’s the first proof of the paradigm-changing potential of entanglement for sensing.”

Australia’s Quantum Technologies Roadmap sees quantum sensors spurring a new wave of technological innovation in healthcare, engineering, transport and resources.

A major success of the team’s quantum microscope was its ability to catapult over a ‘hard barrier’ in traditional light-based microscopy.

“The best light microscopes use bright lasers that are billions of times brighter than the sun,” Professor Bowen said.

“Fragile biological systems like a human cell can only survive a short time in them and this is a major roadblock.

“The quantum entanglement in our microscope provides 35 per cent improved clarity without destroying the cell, allowing us to see minute biological structures that would otherwise be invisible.

“The benefits are obvious – from a better understanding of living systems, to improved diagnostic technologies.”

Professor Bowen said there were potentially boundless opportunities for quantum entanglement in technology.

“Entanglement is set to revolutionise computing, communication and sensing,” he said.

“Absolutely secure communication was demonstrated some decades ago as the first demonstration of absolute quantum advantage over conventional technologies.

“Computing faster than any possible conventional computer was demonstrated by Google two years ago, as the first demonstration of absolute advantage in computing.

“The last piece in the puzzle was sensing, and we’ve now closed that gap.

“This opens the door for some wide-ranging technological revolutions.”

Reference: 

Casacio CA, Madsen LS, Terrasson A, et al. Quantum-enhanced nonlinear microscopy. Nature. 2021;594(7862):201-206. doi: 10.1038/s41586-021-03528-w


Thursday, 27 May 2021

GM's newest vehicle: Off-road, self-driving rover for moon


General Motors is teaming up with Lockheed Martin to produce the ultimate off-road, self-driving, electric vehicles—for the moon.

The project announced Wednesday is still in the early stages and has yet to score any NASA money. But the goal is to design light yet rugged vehicles that will travel farther and faster than the lunar rovers that carried NASA's Apollo astronauts in the early 1970s, the companies said.


"Mobility is really going to open up the moon for us," said Kirk Shireman, a former NASA manager who is now Lockheed Martin's vice president for lunar exploration.

The rovers used by the Apollo 15, 16 and 17 moonwalkers ventured no more than 4 1/2 miles (7.6 kilometers) from their landers. GM also helped design those vehicles.

NASA last year put out a call for industry ideas on lunar rovers. The space agency aims to return astronauts to the moon by 2024, a deadline set by the previous White House.

Their initial rovers will be designed to carry two astronauts at a time, according to company officials. A brief company video showed a large, open rover speeding over lunar slopes, with more headlights in the distance.

This is "just a glimpse of how we see the opportunity playing out," said Jeff Ryder, a vice president for GM Defense.

By operating autonomously when needed, Shireman noted, the rovers can keep astronauts safely away from dangerous spots like the permanently shadowed craters at the moon's South Pole. Frozen water gathered from these dark corners could be used for drinking, growing plants and creating rocket fuel.

Autonomy could also improve efficiency, with astronauts focused on collecting rocks as a rover follows behind like a puppy, he said.

In a separate venture begun two years ago, Toyota partnered with the Japanese Space Agency to build a pressurized electric-powered lunar rover for astronauts. They're calling it the Lunar Cruiser.


GM and Lockheed Martin's vehicle will be unpressurized, meaning that riders will need to wear spacesuits at all times. There's room for both models, according to Shireman.

Monday, 17 May 2021

NASA Set To Test New Space Laser Communication Systems


Launching this summer, NASA’s Laser Communications Relay Demonstration (LCRD) will showcase the dynamic powers of laser communications technologies. With NASA’s ever-increasing human and robotic presence in space, missions can benefit from a new way of “talking” with Earth.

Since the beginning of spaceflight in the 1950s, NASA missions have leveraged radio frequency communications to send data to and from space. Laser communications, also known as optical communications, will further empower missions with unprecedented data capabilities.


Why Lasers?

As science instruments evolve to capture high-definition data like 4K video, missions will need expedited ways to transmit information to Earth. With laser communications, NASA can significantly accelerate the data transfer process and empower more discoveries.

Laser communications will enable 10 to 100 times more data transmitted back to Earth than current radio frequency systems. It would take roughly nine weeks to transmit a complete map of Mars back to Earth with current radio frequency systems. With lasers, it would take about nine days.

Additionally, laser communications systems are ideal for missions because they need less volume, weight, and power. Less mass means more room for science instruments, and less power means less of a drain of spacecraft power systems. These are all critically important considerations for NASA when designing and developing mission concepts.

“LCRD will demonstrate all of the advantages of using laser systems and allow us to learn how to use them best operationally,” said Principal Investigator David Israel at NASA’s Goddard Space Flight Center in Greenbelt, Maryland. “With this capability further proven, we can start to implement laser communications on more missions, making it a standardized way to send and receive data.”

How it Works

Both radio waves and infrared light are electromagnetic radiation with wavelengths at different points on the electromagnetic spectrum. Like radio waves, infrared light is invisible to the human eye, but we encounter it every day with things like television remotes and heat lamps.

Missions modulate their data onto the electromagnetic signals to traverse the distances between spacecraft and ground stations on Earth. As the communication travels, the waves spread out.

The infrared light used for laser communications differs from radio waves because the infrared light packs the data into significantly tighter waves, meaning ground stations can receive more data at once. While laser communications aren’t necessarily faster, more data can be transmitted in one downlink.

Laser communications terminals in space use narrower beam widths than radio frequency systems, providing smaller “footprints” that can minimize interference or improve security by drastically reducing the geographic area where someone could intercept a communications link. However, a laser communications telescope pointing to a ground station must be exact when broadcasting from thousands or millions of miles away. A deviation of even a fraction of a degree can result in the laser missing its target entirely. Like a quarterback throwing a football to a receiver, the quarterback needs to know where to send the football, i.e. the signal, so that the receiver can catch the ball in stride. NASA’s laser communications engineers have intricately designed laser missions to ensure this connection can happen.

Laser Communications Relay Demonstration

Located in geosynchronous orbit, about 22,000 miles above Earth, LCRD will be able to support missions in the near-Earth region. LCRD will spend its first two years testing laser communications capabilities with numerous experiments to refine laser technologies further, increasing our knowledge about potential future applications.

LCRD’s initial experiment phase will leverage the mission’s ground stations in California and Hawaii, Optical Ground Station 1 and 2, as simulated users. This will allow NASA to evaluate atmospheric disturbances on lasers and practice switching support from one user to the next. After the experiment phase, LCRD will transition to supporting space missions, sending and receiving data to and from satellites over infrared lasers to demonstrate the benefits of a laser communications relay system.

The first in-space user of LCRD will be NASA’s Integrated LCRD Low-Earth Orbit User Modem and Amplifier Terminal (ILLUMA-T), which is set to launch to the International Space Station in 2022. The terminal will receive high-quality science data from experiments and instruments onboard the space station and then transfer this data to LCRD at 1.2 gigabits per second. LCRD will then transmit it to ground stations at the same rate.

LCRD and ILLUMA-T follow the groundbreaking 2013 Lunar Laser Communications Demonstration, which downlinked data over a laser signal at 622 megabits-per-second, proving the capabilities of laser systems at the Moon. NASA has many other laser communications missions currently in different stages of development. Each of these missions will increase our knowledge about the benefits and challenges of laser communications and further standardize the technology.

LCRD is slated to launch as a payload on a Department of Defense spacecraft on June 23, 2021.


Credit: NASA Goddard 

Saturday, 8 May 2021

Researchers have designed the world's highest intensity laser: 100 trillion watts per cm²


Researchers have demonstrated a record-high laser pulse intensity of over 1023 W/cm2 using the petawatt laser at the Center for Relativistic Laser Science (CoReLS), Institute for Basic Science in the Republic of Korea. It took more than a decade to reach this laser intensity, which is ten times that reported by a team at the University of Michigan in 2004. These ultrahigh intensity light pulses will enable exploration of complex interactions between light and matter in ways not possible before.


The powerful laser can be used to examine phenomena believed to be responsible for high-power cosmic rays, which have energies of more than a quadrillion (1015) electronvolts (eV). Although scientists know that these rays originate from somewhere outside our solar system, how they are made and what is forming them has been a longstanding mystery.

"This high intensity laser will allow us to examine astrophysical phenomena such as electron-photon and photon-photon scattering in the lab," said Chang Hee Nam, director of CoReLS and professor at Gwangju Institute of Science & Technology. "We can use it to experimentally test and access theoretical ideas, some of which were first proposed almost a century ago."

In Optica, The Optical Society's (OSA) journal for high impact research, the researchers report the results of years of work to increase the intensity of laser pulses from the CoReLS laser. Studying laser matter-interactions requires a tightly focused laser beam and the researchers were able to focus the laser pulses to a spot size of just over one micron, less than one fiftieth the diameter of a human hair. The new record-breaking laser intensity is comparable to focusing all the light reaching earth from the sun to a spot of 10 microns.

"This high intensity laser will let us tackle new and challenging science, especially strong field quantum electrodynamics, which has been mainly dealt with by theoreticians," said Nam. "In addition to helping us better understand astrophysical phenomena, it could also provide the information necessary to develop new sources for a type of radiation treatment that uses high-energy protons to treat cancer."

Making pulses more intense

The new accomplishment extends previous work in which the researchers demonstrated a femtosecond laser system, based on Ti:Sapphire, that produces 4 petawatt (PW) pulses with durations of less than 20 femtoseconds while focused to a 1 micrometer spot. This laser, which was reported in 2017, produced a power roughly 1,000 times larger than all the electrical power on Earth in a laser pulse that only lasts twenty quadrillionths of a second.

To produce high-intensity laser pulses on target, the generated optical pulses must be focused extremely tightly. In this new work, the researchers apply an adaptive optics system to precisely compensate optical distortions. This system involves deformable mirrors -- which have a controllable reflective surface shape -- to precisely correct distortions in the laser and generate a beam with a very well-controlled wavefront. They then used a large off-axis parabolic mirror to achieve an extremely tight focus. This process requires delicate handling of the focusing optical system.

"Our years of experience gained while developing ultrahigh power lasers allowed us to accomplish the formidable task of focusing the PW laser with the beam size of 28 cm to a micrometer spot to accomplish a laser intensity exceeding 1023 W/cm2," said Nam.

Studying high-energy processes

The researchers are using these high-intensity pulses to produce electrons with an energy over 1 GeV (109 eV) and to work in the nonlinear regime in which one electron collides with several hundred laser photons at once. This process is a type of strong field quantum electrodynamics called nonlinear Compton scattering, which is thought to contribute to the generation of extremely energetic cosmic rays.

They will also use the radiation pressure created by the ultrahigh intensity laser to accelerate protons. Understanding how this process occurs could help develop a new laser-based proton source for cancer treatments. Sources used in today's radiation treatments are generated using an accelerator that requires a huge radiation shield. A laser-driven proton source is expected to reduce the system cost, making the proton oncology machine less costly and thus more widely accessible to patients.

The researchers continue to develop new ideas for enhancing the laser intensity even more without significantly increasing the size of the laser system. One way to accomplish this would be to figure out a new way to reduce the laser pulse duration. As lasers with peaks power ranging from 1 to 10 PW are now in operation and several facilities reaching 100 PW are being planned, there is no doubt that high-intensity physics will progress tremendously in the near future.


Reference:

Jin Woo Yoon, Yeong Gyu Kim, Il Woo Choi, Jae Hee Sung, Hwang Woon Lee, Seong Ku Lee, Chang Hee Nam. Realization of laser intensity over 1023  W/cm2. Optica, 2021; 8 (5): 630 DOI: 10.1364/OPTICA.420520

Friday, 4 December 2020

Battery of tests: Scientists figure out how to track what happens inside batteries


The future of mobility is electric cars, trucks and airplanes. But there is no way a single battery design can power that future. Even your cell phone and laptop batteries have different requirements and different designs. The batteries we will need over the next few decades will have to be tailored to their specific uses.

And that means understanding exactly what happens, as precisely as possible, inside each type of battery. Every battery works on the same principle: ions, which are atoms or molecules with an electrical charge, carry a current from the anode to the cathode through material called the electrolyte, and then back again. But their precise movement through that material, whether liquid or solid, has puzzled scientists for decades. Knowing exactly how different types of ions move through different types of electrolytes will help researchers figure out how to affect that movement, to create batteries that charge and discharge in ways most befitting their specific uses.


In a breakthrough discovery, a team of scientists has demonstrated a combination of techniques that allows for the precise measurement of ions moving through a battery. Using the Advanced Photon Source (APS), a U.S. Department of Energy (DOE) Office of Science User Facility at DOE's Argonne National Laboratory, these researchers have not only peered inside a battery as it operates, measuring the reactions in real time, but have opened the door to similar experiments with different types of batteries.

The researchers collaborated on this result with the Joint Center for Energy Storage Research (JCESR), a DOE Energy Innovation Hub led by Argonne. The team's paper, which details velocities of lithium ions moving through a polymer electrolyte, was published in Energy and Environmental Science.

"This is a combination of different experimental methods to measure velocity and concentration, and then compare them both to theory," said Hans-Georg Steinrück, professor at Paderborn University in Germany and the first author on the paper. "We showed this is possible, and now we will perform it on other systems that are different in nature."

Those methods, performed at beamline 8-ID-I at the APS, included using ultra-bright X-rays to measure the velocity of the ions moving through the battery, and to simultaneously measure the concentration of ions within the electrolyte, while a model battery discharged. The research team then compared their results with mathematical models. Their result is an extremely accurate figure representing the current carried by ions—what is called the transport number.

The transport number is essentially the amount of current carried by positively charged ions in relation to the overall electric current, and the team's calculations put that number at approximately 0.2. This conclusion differs from those derived by other methods, researchers said, due to the sensitivity of this new way of measuring ion movement.

The true value transport number has been the subject of some debate among scientists for years, according to Michael Toney, professor at the University of Colorado Boulder and an author on the paper. Toney and Steinrück were both staff scientists at the DOE's SLAC National Accelerator Laboratory when this research was conducted.

"The traditional way of measuring the transport number is to analyze the current," Toney said. "But it was unknown how much of that current is due to lithium ions and how much is due to other things you don't want in your analysis. The principle is easy, but we had to measure accurately. This was certainly a proof of concept."

For this experiment the research team used a solid polymer electrolyte, instead of the liquid ones in wide use for lithium ion batteries. As Toney notes, polymers are safer, since they avoid the flammability issues of some liquid electrolytes.


Argonne's Venkat Srinivasan, deputy director of JCESR and an author on the paper, has extensive experience modeling the reactions inside batteries, but this is the first time he's been able to compare those models to real-time data on the movement of ions through an electrolyte.

"For years we wrote papers about what happens inside a battery, since we couldn't see the things inside," he said. "I always joked that whatever I said must be true, since we couldn't confirm it. So for decades we have been looking for information like this, and it challenges people like me who have been making the predictions."

In the past, Srinivasan said, the best way to research the inner workings of batteries was to send a current through them and then analyze what happened afterward. The ability to trace the ions moving in real time, he said, offers scientists a chance to change that movement to suit their battery design needs.

"We had to connect the dots before, and now we can directly detect the ions," he said. "There is no ambiguity."

Eric Dufresne, physicist with Argonne's X-ray Science Division, was one of the APS scientists who worked on this project. An author on the paper, Dufresne said the experiment made use of the coherence available at the APS, allowing the research team to capture the effect they were looking for down to velocities of only nanometers per second.

"This is a very thorough and complex study," he said. "It's a nice example of combining X-ray techniques in a novel way, and a good step toward developing future applications."

Dufresne and his colleagues also noted that these experiments will only improve once the APS undergoes an in-progress upgrade of its electron storage ring, which will increase the brightness of the X-rays it produces by up to 500 times.

"The APS Upgrade will allow us to push these dynamic studies to better than microseconds," Dufresne said. "We will be able to focus the beam for smaller measurements and get through thicker materials. The upgrade will give us unique capabilities, and we will be able to do more experiments of this type."

That's a prospect that excites the research team. Steinrück said the next step is to analyze more complex polymers and other materials, and eventually into liquid electrolytes. Toney said he would like to examine ions from other types of material, like calcium and zinc.

Examining a diversity of materials, Srinivasan said, would be important for the eventual goal: batteries that are precisely designed for their individual uses.

"If we want to create high-energy, fast, safe, long-lasting batteries, we need to know more about ion motion," he said. "We need to understand more about what happens inside a battery, and use that knowledge to design new materials from the bottom up."


More information: 

Hans-Georg Steinrück et al. Concentration and velocity profiles in a polymeric lithium-ion battery electrolyte, Energy & Environmental Science (2020). DOI: 10.1039/D0EE02193H

Tuesday, 22 September 2020

Researchers identify new type of superconductor

Until now, the history of superconducting materials has been a tale of two types: s-wave and d-wave.

Now, Cornell researchers – led by Brad Ramshaw, the Dick & Dale Reis Johnson Assistant Professor in the College of Arts and Sciences – have discovered a possible third type: g-wave.



Their paper, “Thermodynamic Evidence for a Two-Component Superconducting Order Parameter in Sr2RuO4,” published Sept. 21 in Nature Physics. The lead author is doctoral student Sayak Ghosh, M.S. ’19.

Electrons in superconductors move together in what are known as Cooper pairs. This “pairing” endows superconductors with their most famous property – no electrical resistance – because, in order to generate resistance, the Cooper pairs have to be broken apart, and this takes energy.

In s-wave superconductors – generally conventional materials, such as lead, tin and mercury – the Cooper pairs are made of one electron pointing up and one pointing down, both moving head-on toward each other, with no net angular momentum. In recent decades, a new class of exotic materials has exhibited what’s called d-wave superconductivity, whereby the Cooper pairs have two quanta of angular momentum.

Physicists have theorized the existence of a third type of superconductor between these two so-called “singlet” states: a p-wave superconductor, with one quanta of angular momentum and the electrons pairing with parallel rather than antiparallel spins. This spin-triplet superconductor would be a major breakthrough for quantum computing because it can be used to create Majorana fermions, a unique particle which is its own antiparticle.

This illustration shows a crystal lattice of strontium ruthenate responding to various sound waves sent via resonant ultrasound spectroscopy as the material cools through its superconducting transition at 1.4 kelvin (minus 457 degrees Fahrenheit). The highlighted deformation suggests the material may be a new type of superconductor. 


For more than 20 years, one of the leading candidates for a p-wave superconductor has been strontium ruthenate (Sr2RuO4­), although recent research has started to poke holes in the idea.

Ramshaw and his team set out to determine once and for all whether strontium ruthenate is a highly desired p-wave superconductor. Using high-resolution resonant ultrasound spectroscopy, they discovered that the material is potentially an entirely new kind of superconductor altogether: g-wave.

“This experiment really shows the possibility of this new type of superconductor that we had never thought about before,” Ramshaw said. “It really opens up the space of possibilities for what a superconductor can be and how it can manifest itself. If we’re ever going to get a handle on controlling superconductors and using them in technology with the kind of fine-tuned control we have with semiconductors, we really want to know how they work and what varieties and flavors they come in.”

As with previous projects, Ramshaw and Ghosh used resonant ultrasound spectroscopy to study the symmetry properties of the superconductivity in a crystal of strontium ruthenate that was grown and precision-cut by collaborators at the Max Planck Institute for Chemical Physics of Solids in Germany.

However, unlike previous attempts, Ramshaw and Ghosh encountered a significant problem when trying to conduct the experiment.

“Cooling down resonant ultrasound to 1 kelvin (minus 457.87 degrees Fahrenheit) is difficult, and we had to build a completely new apparatus to achieve this,” Ghosh said.

With their new setup, the Cornell team measured the response of the crystal’s elastic constants – essentially the speed of sound in the material – to a variety of sound waves as the material cooled through its superconducting transition at 1.4 kelvin (minus 457 degrees Fahrenheit).

“This is by far the highest-precision resonant ultrasound spectroscopy data ever taken at these low temperatures,” Ramshaw said.

Based on the data, they determined that strontium ruthenate is what’s called a two-component superconductor, meaning the way electrons bind together is so complex, it can’t be described by a single number; it needs a direction as well.

Previous studies had used nuclear magnetic resonance (NMR) spectroscopy to narrow the possibilities of what kind of wave material strontium ruthenate might be, effectively eliminating p-wave as an option.

By determining that the material was two-component, Ramshaw’s team not only confirmed those findings, but also showed strontium ruthenate wasn’t a conventional s- or d-wave superconductor, either.

“Resonant ultrasound really lets you go in and even if you can’t identify all the microscopic details, you can make broad statements about which ones are ruled out,” Ramshaw said. “So then the only things that the experiments are consistent with are these very, very weird things that nobody has ever seen before. One of which is g-wave, which means angular momentum 4. No one has ever even thought that there would be a g-wave superconductor.”

Now the researchers can use the technique to examine other materials to find out if they are potential p-wave candidates.

However, the work on strontium ruthenate isn’t finished.

“This material is extremely well studied in a lot of different contexts, not just for its superconductivity,” Ramshaw said. “We understand what kind of metal it is, why it’s a metal, how it behaves when you change temperature, how it behaves when you change the magnetic field. So you should be able to construct a theory of why it becomes a superconductor better here than just about anywhere else.”



More information: 

Thermodynamic evidence for a two-component superconducting order parameter in Sr2RuO4,
DOI: 10.1038/s41567-020-1032-4

Thursday, 17 September 2020

Researchers develop the world's smallest ultrasound detector


Researchers at Helmholtz Zentrum München and the Technical University of Munich (TUM) have developed the world's smallest ultrasound detector. It is based on miniaturized photonic circuits on top of a silicon chip. With a size 100 times smaller than an average human hair, the new detector can visualize features that are much smaller than previously possible, leading to what is known as super-resolution imaging.



Since the development of medical ultrasound imaging in the 1950s, the core detection technology of ultrasound waves has primarily focused on using piezoelectric detectors, which convert the pressure from ultrasound waves into electric voltage. The imaging resolution achieved with ultrasound depends on the size of the piezoelectric detector employed. Reducing this size leads to higher resolution and can offer smaller, densely packed one or two dimensional ultrasound arrays with improved ability to discriminate features in the imaged tissue or material. However, further reducing the size of piezoelectric detectors impairs their sensitivity dramatically, making them unusable for practical application.

Using computer chip technology to create an optical ultrasound detector

Silicon photonics technology is widely used to miniaturize optical components and densely pack them on the small surface of a silicon chip. While silicon does not exhibit any piezoelectricity, its ability to confine light in dimensions smaller than the optical wavelength has already been widely exploited for the development of miniaturized photonic circuits.

Researchers at Helmholtz Zentrum Munchen and TUM capitalized on the advantages of those miniaturized photonic circuits and built the world's smallest ultrasound detector: the silicon waveguide-etalon detector, or SWED. Instead of recording voltage from piezoelectric crystals, SWED monitors changes in light intensity propagating through the miniaturized photonic circuits.

"This is the first time that a detector smaller than the size of a blood cell is used to detect ultrasound using the silicon photonics technology," says Rami Shnaiderman, developer of SWED. "If a piezoelectric detector was miniaturized to the scale of SWED, it would be 100 million times less sensitive."

Super-resolution imaging

"The degree to which we were we able to miniaturize the new detector while retaining high sensitivity due to the use of silicon photonics was breathtaking," says Prof. Vasilis Ntziachristos, lead of the research team. The SWED size is about half a micron (=0,0005 millimeters). This size corresponds to an area that is at least 10,000 times smaller than the smallest piezoelectric detectors employed in clinical imaging applications. The SWED is also up to 200 times smaller than the ultrasound wavelength employed, which means that it can be used to visualize features that are smaller than one micrometer, leading to what is called super-resolution imaging.

Inexpensive and powerful

As the technology capitalizes on the robustness and easy manufacturability of the silicon platform, large numbers of detectors can be produced at a small fraction of the cost of piezoelectric detectors, making mass production feasible. This is important for developing a number of different detection applications based on ultrasound waves. "We will continue to optimize every parameter of this technology—the sensitivity, the integration of SWED in large arrays, and its implementation in hand-held devices and endoscopes," adds Shnaiderman.

Future development and applications

"The detector was originally developed to propel the performance of optoacoustic imaging, which is a major focus of our research at Helmholtz Zentrum München and TUM. However, we now foresee applications in a broader field of sensing and imaging," says Ntziachristos.

While the researchers are primarily aiming for applications in clinical diagnostics and basic biomedical research, industrial applications may also benefit from the new technology. The increased imaging resolution may lead to studying ultra-fine details in tissues and materials. A first line of investigation involves super-resolution optoacoustic (photoacoustic) imaging of cells and micro-vasculature in tissues, but the SWED could be also used to study fundamental properties of ultrasonic waves and their interactions with matter on a scale that was not possible before.

The study is published in Nature.



More information: 

Shnaiderman, R., Wissmeyer, G., Ülgen, O. et al. A submicrometre silicon-on-insulator resonator for ultrasound detection. Nature, DOI: 10.1038/s41586-020-2685-y

Saturday, 12 September 2020

Computational modelling explains why blues and greens are brightest colors in nature


Researchers have shown why intense, pure red colors in nature are mainly produced by pigments, instead of the structural color that produces bright blue and green hues.



The researchers, from the University of Cambridge, used a numerical experiment to determine the limits of matt structural color—a phenomenon which is responsible for some of the most intense colors in nature—and found that it extends only as far as blue and green in the visible spectrum. The results, published in PNAS, could be useful in the development of non-toxic paints or coatings with intense color that never fades.

Structural color, which is seen in some bird feathers, butterfly wings or insects, is not caused by pigments or dyes, but internal structure alone. The appearance of the color, whether matt or iridescent, will depending on how the structures are arranged at the nanoscale.

Ordered, or crystalline, structures result in iridescent colors, which change when viewed from different angles. Disordered, or correlated, structures result in angle-independent matt colors, which look the same from any viewing angle. Since structural color does not fade, these angle-independent matt colors would be highly useful for applications such as paints or coatings, where metallic effects are not wanted.

"In addition to their intensity and resistance to fading, a matt paint which uses structural color would also be far more environmentally-friendly, as toxic dyes and pigments would not be needed," said first author Gianni Jacucci from Cambridge's Department of Chemistry. "However, we first need to understand what the limitations are for recreating these types of colors before any commercial applications are possible."

"Most of the examples of structural color in nature are iridescent—so far, examples of naturally-occurring matt structural color only exist in blue or green hues," said co-author Lukas Schertel. "When we've tried to artificially recreate matt structural color for reds or oranges, we end up with a poor-quality result, both in terms of saturation and color purity."

The researchers, who are based in the lab of Dr. Silvia Vignolini, used numerical modeling to determine the limitations of creating saturated, pure and matt red structural color.

The researchers modeled the optical response and color appearance of nanostructures, as found in the natural world. They found that saturated, matt structural colors cannot be recreated in the red region of the visible spectrum, which might explain the absence of these hues in natural systems.

"Because of the complex interplay between single scattering and multiple scattering, and contributions from correlated scattering, we found that in addition to red, yellow and orange can also hardly be reached," said Vignolini.

Despite the apparent limitations of structural color, the researchers say these can be overcome by using other kind of nanostructures, such as network structures or multi-layered hierarchical structures, although these systems are not fully understood yet.



More information: 

Gianni Jacucci et al, The limitations of extending nature's color palette in correlated, disordered systems, Proceedings of the National Academy of Sciences (2020). DOI: 10.1073/pnas.2010486117

Friday, 4 September 2020

To make a better sensor, just add some noise


Adding noise to enhance a weak signal is a sensing phenomenon common in the animal world but unusual in manmade sensors. Now Penn State researchers have added a small amount of background noise to enhance very weak signals in a light source too dim to sense.



In contrast to most sensors, for which noise is a problem that should be suppressed, they found that adding just the right amount of background noise can actually increase a signal too weak for sensing by normal sensors, to a level that can reach detectability.

Although their sensor, based on a two-dimensional material called molybdenum disulfide, detects light, the same principle can be used to detect other signals, and because it requires very little energy and space compared to conventional sensors, could find wide adaptation in the coming Internet of Things (IoT). IoT will deploy tens of millions of sensors to monitor conditions in the home and factories, and low energy requirements would be a strong bonus.

"This phenomenon is something that is frequently seen in nature," says Saptarshi Das, an assistant professor of engineering science and mechanics. "For example, a paddlefish that lives in muddy waters cannot actually find its food, which is a phytoplankton called Daphnia, by sight. The paddlefish has electroreceptors that can pick up very weak electric signal from the Daphnia at up to 50 meters. If you add a little bit of noise, it can find the Daphnia at 75 meters or even 100 meters. This ability adds to the evolutionary success of this animal."

Another interesting example is the jewel beetle, which can detect a forest fire at 50 miles distance. The most advanced infrared detector can only detect at 10 to 20 miles. This is due to a phenomenon these animals use called stochastic resonance.

"Stochastic resonance is a phenomenon where a weak signal which is below the detection threshold of a sensor can be detected in the presence of a finite and appropriate amount of noise," according to Akhil Dodda, a graduate student in engineering science and mechanics and co-first author on a new paper appearing this week in Nature Communications.

In their paper, the researchers demonstrate the first use of this technique to detect a subthreshold photonic signal.

One possible use being considered is for troops in combat. Army personnel in the field already carry very bulky equipment. It is unfeasible to add the heavy, power-hungry equipment required to enhance a subthreshold signal. Their technique is also applicable in resource-constrained environments or beneath the ocean where people want to monitor very weak signals. It could also be used in volcanic locations or to monitor earthquakes in time to give an alarm.

"Who would have thought that noise could play a constructive role in signal detection? We have challenged tradition to detect otherwise undetectable signals with miniscule energy consumption. This can open doors to a totally unexplored and ignored field of noise enhanced signal detection," said Aaryan Oberoi, a graduate student from the Department of Engineering Science and Mechanics and co-first author on the paper.

Their next step is to demonstrate this technique on a silicon photodiode, which would make the device very scalable. Any state-of-the art sensor can be enhanced by this concept, Das says.



More information: 

Akhil Dodda et al, Stochastic resonance in MoS2 photodetector, Nature Communications (2020). DOI: 10.1038/s41467-020-18195-0

Wednesday, 26 August 2020

Storing information in antiferromagnetic materials


Researchers at Mainz University were able to show that information can be stored in antiferromagnetic materials and to measure the efficiency of the writing operation.



We all store more and more information, while the end devices are supposed to get smaller and smaller. However, due to continuous technological improvement, conventional electronics based on silicon is rapidly reaching its limits -- for example limits of physical nature such as the bit size or the number of electrons required to store information. Spintronics, and antiferromagnetic materials in particular, offers an alternative. It is not only electrons that are used to store information, but also their spin containing magnetic information. In this way, twice as much information can be stored in the same room. So far, however, it has been controversial whether it is even possible to store information electrically in antiferromagnetic materials.

Physicists unveil the potential of antiferromagnetic materials

Researchers at Johannes Gutenberg University Mainz (JGU), in collaboration with Tohoku University in Sendai in Japan, have now been able to prove that it works: "We were not only able to show that information storage in antiferromagnetic materials is fundamentally possible, but also to measure how efficiently information can be written electrically in insulating antiferromagnetic materials," said Dr. Lorenzo Baldrati, Marie Sklowdoska-Curie Fellow in Professor Mathias Kläui's group at JGU. For their measurements, the researchers used the antiferromagnetic insulator Cobalt oxide CoO -- a model material that paves the way for applications. The result: Currents are much more efficient than magnetic fields to manipulate antiferromagnetic materials. This discovery opens the way toward applications ranging from smart cards that cannot be erased by external magnetic fields to ultrafast computers -- thanks to the superior properties of antiferromagnets over ferromagnets. The research paper has recently been published in Physical Review Letters. In further steps, the researchers at JGU want to investigate how quickly information can be saved and how "small" the memory can be written to.

Active German-Japanese exchange

"Our longstanding collaboration with the leading university in the field of spintronics, Tohoku University, has generated another exciting piece of work," emphasized Professor Mathias Kläui. "With the support of the German Exchange Service, the Graduate School of Excellence Materials Science in Mainz, and the German Research Foundation, we initiated a lively exchange between Mainz and Sendai, working with theory groups at the forefront of this topic. We have opportunities for first joint degrees between our universities, which is noticed by students. This is a next step in the formation of an international team of excellence in the burgeoning field of antiferromagnetic spintronics."



Reference:

L. Baldrati et al. Efficient Spin Torques in Antiferromagnetic CoO/Pt Quantified by Comparing Field- and Current-Induced Switching. Physical Review Letters, 2020 DOI: 10.1103/PhysRevLett.125.077201

Sunday, 28 June 2020

Chemistry paves the way for improved electronic materials


Indium nitride is a promising material for use in electronics, but difficult to manufacture. Scientists at LiU have developed a new molecule that can be used to create high-quality indium nitride, making it possible to use it in, for example, high-frequency electronics.



The bandwidth we currently use for wireless data transfer will soon be full. If we are to continue transmitting ever-increasing amounts of data, the available bandwidth must be increased by bringing further frequencies into use. Indium nitride may be part of the solution.

"Since electrons move through indium nitride extremely easily, it is possible to send electrons backwards and forwards through the material at very high speeds, and create signals with extremely high frequencies. This means that indium nitride can be used in high-frequency electronics, where it can provide, for example, new frequencies for wireless data transfer," says Henrik Pedersen, professor of inorganic chemistry at the Department of Physics, Chemistry and Biology at Linköping University. He has led the study, which was recently published in Chemistry of Materials.

Indium nitride consists of nitrogen and a metal, indium. It is a semiconductor and can therefore be used in transistors, on which all electronic devices are based. The problem is that it is difficult to produce thin films of indium nitride. Thin films of similar semiconductor materials are often produced using a well-established method known as chemical vapour deposition, or CVD, in which temperatures between 800 and 1,000 degrees Celsius are used. However, indium nitride breaks down into its constituents, indium and nitrogen, when it is heated above 600 degrees Celsius.

The scientists who conducted the present study have used a variant of CVD known as atomic layer deposition, or ALD, in which lower temperatures are used. They have developed a new molecule, known as an indium triazenide. No one had worked with such indium triazenides previously, and the LiU researchers soon discovered that the triazenide molecule is an excellent starting material for the manufacture of thin films. Most materials used in electronics must be produced by allowing a thin film to grow on a surface that controls the crystal structure of the electronic material. The process is known as epitaxial growth. The researchers discovered that it is possible to achieve epitaxial growth of indium nitride if silicon carbide is used as substrate, something that was not previously known. Furthermore, the indium nitride produced in this way is extremely pure, and among the highest quality indium nitride in the world.



"The molecule that we have produced, an indium triazenide, makes it possible to use indium nitride in electronic devices. We have shown that it is possible to produce indium nitride in a manner that ensures that it is sufficiently pure to be described as a true electronic material," says Henrik Pedersen.

The researchers discovered another surprising fact. It is generally accepted among those who use ALD that the molecules should not be allowed to react or be broken down in any way in the gas phase. But when the researchers changed the temperature of the coating process, they discovered that there is not just one, but two, temperatures at which the process was stable.

"The indium triazenide breaks down into smaller fragments in the gas phase, and this improves the ALD process. This is a paradigm shift within ALD -- using molecules that are not fully stable in the gas phase. We show that we can obtain a better final result if we allow the new molecule to break down to a certain extent in the gas phase," says Henrik Pedersen.

The researchers are now examining similar triazenide molecules with other metals than indium, and have obtained promising results when using these to produce molecules for ALD.



Reference:

Nathan J. O’Brien, Polla Rouf, Rouzbeh Samii, Karl Rönnby, Sydney C. Buttera, Chih-Wei Hsu, Ivan G. Ivanov, Vadim Kessler, Lars Ojamäe, Henrik Pedersen. In Situ Activation of an Indium(III) Triazenide Precursor for Epitaxial Growth of Indium Nitride by Atomic Layer Deposition. Chemistry of Materials, 2020; 32 (11): 4481 DOI: 10.1021/acs.chemmater.9b05171

Tuesday, 23 June 2020

Measuring a tiny quasiparticle is a major step forward for semiconductor technology


A team of researchers led by Sufei Shi, an assistant professor of chemical and biological engineering at Rensselaer Polytechnic Institute, has uncovered new information about the mass of individual components that make up a promising quasiparticle, known as an exciton, that could play a critical role in future applications for quantum computing, improved memory storage, and more efficient energy conversion.



Published today in Nature Communications, the team's work brings researchers one step closer to advancing the development of semiconductor devices by deepening their understanding of an atomically thin class of materials known as transitional metal dichalcogenides (TMDCs), which have been eyed for their electronic and optical properties. Researchers still have a lot to learn about the exciton before TMDCs can successfully be used in technological devices.

Shi and his team have become leaders in that pursuit, developing and studying TMDCs, and the exciton in particular. Excitons are typically generated by energy from light and form when a negatively charged electron bonds with a positively charged hole particle.

The Rensselaer team found that within this atomically thin semiconductor material, the interaction between electrons and holes can be so strong that the two particles within an exciton can bond with a third electron or hole particle to form a trion.

In this new study, Shi's team was able to manipulate the TMDCs material so the crystalline lattice within would vibrate, creating another type of quasiparticle known as a phonon, which will strongly interact with a trion. The researchers then placed the material within a high magnetic field, analyzed the light emitted from the TMDCs from the phonon interaction, and were able to determine the effective mass of the electron and hole individually.

Researchers previously assumed there would be symmetry in mass, but, Shi said, the Rensselaer team found these measurements were significantly different.

"We have developed a lot of knowledge about TMDCs now," Shi said. "But in order to design an electronic or optoelectronic device, it is essential to know the effective mass of the electrons and holes. This work is one solid step toward that goal."



More information: 

Zhipeng Li et al. Phonon-exciton Interactions in WSe2 under a quantizing magnetic field, Nature Communications (2020). DOI: 10.1038/s41467-020-16934-x

Thursday, 11 June 2020

Scientists observe quantum 'fifth state of matter' in space for the first time


Scientists have observed the fifth state of matter in space for the first time, offering unprecedented insight that could help solve some of the quantum universe's most intractable conundrums, research showed Thursday.

Bose-Einstein condensates (BECs) – the existence of which was predicted by Albert Einstein and Indian mathematician Satyendra Nath Bose almost a century ago – are formed when atoms of certain elements are cooled to near absolute zero (0 Kelvin, minus 273.15 Celsius).

At this point, the atoms become a single entity with quantum properties, wherein each particle also functions as a wave of matter.



BECs straddle the line between the macroscopic world governed by forces such as gravity and the microscopic plane, ruled by quantum mechanics.

Scientists believe BECs contain vital clues to mysterious phenomena such as dark energy – the unknown energy thought to be behind the universe's accelerating expansion.

But BECs are extremely fragile. The slightest interaction with the external world is enough to warm them past their condensation threshold.

This makes them nearly impossible for scientists to study on Earth, where gravity interferes with the magnetic fields required to hold them in place for observation.

On Thursday a team of NASA scientists unveiled the first results from BEC experiments aboard the International Space Station (ISS), where particles can be manipulated free from earthly constraints.

"Microgravity allows us to confine atoms with much weaker forces since we don't have to support them against gravity," Robert Thompson of from the California Institute for Technology, Pasadena, told Agence France-Presse (AFP).

The research published in the journal Nature documents several startling differences in the properties of BECs created on Earth and those aboard the ISS.

For one thing, BECs in terrestrial labs typically last a handful of milliseconds before dissipating.

Aboard the ISS the BECs lasted more than a second, offering the team an unprecedented chance to study their properties.

Microgravity also allowed the atoms to be manipulated by weaker magnetic fields, speeding their cooling and allowing clearer imaging.



'Remarkable' breakthrough

Creating the fifth state of matter, especially within the physical confines of a space station, is no small feat.

First, bosons – atoms that have an equal number of protons and electrons – are cooled to absolute zero using lasers to clamp them in place.

The slower the atoms move around, the cooler they become.

As they lose heat, a magnetic field is introduced to keep them from moving and each particle's wave expands, cramming many bosons into a microscopic "trap" that causes their waves to overlap into a single matter wave – a property known as quantum degeneracy.

The second the magnetic trap is released in order for scientists to study the condensate, however, the atoms begin to repel each other, causing the cloud to fly apart and the BECs to becomes too dilute to detect.

Thompson and the team realized that the microgravity onboard the ISS allowed them to create BECs from rubidium – a soft metal similar to potassium – on a far shallower trap than on Earth. This accounted for the vastly increased time the condensate could be studied before diffusing.

"Most importantly we can observe the atoms as they float entirely unconfined (and hence unperturbed) by external forces," Thompson said.

Previous studies trying to emulate the effect of weightlessness on BECs used airplanes in free fall, rockets and even apparatus dropped from various heights.



Research team leader David Aveline told AFP that studying BECs in microgravity opened up a host of research opportunities.

"Applications range from tests of general relativity and searches for dark energy and gravitational waves to spacecraft navigation and prospecting for subsurface minerals on the moon and other planetary bodies," he said.

References:

David C. Aveline et al. Observation of Bose–Einstein condensates in an Earth-orbiting research lab, Nature (2020). DOI: 10.1038/s41586-020-2346-1

Maike D. Lachmann et al. Quantum matter orbits Earth, Nature (2020). DOI: 10.1038/d41586-020-01653-6

Saturday, 8 February 2020

A new quasiparticle is discovered: Pi-ton

Two electrons and two gaps, conjugated by the injection of a photon, remain together, forming the quasiparticle Π-ton.


There are very different types of particles: Elementary particles are the fundamental blocks of matter. Atoms, for example, are "linked" - or associated - states that consist of several minor constituents, such as quarks.

And there are so-called "quasiparticles" - excitations in a system formed by many particles, but which behave together exactly as if they were a single particle.



It is one of those complex particles - dubbed Π-ton - that was discovered by Anna Kauch and her colleagues at the Vienna University of Technology, Austria.

In addition to describing the behavior of Pi-ton in simulations, the team also indicated the way for experimentalists to detect it in the laboratory.


Quasiparticles

The simplest and most well-known quasiparticle is the Hole, the carrier of positive charge. When an electron, which carries the negative charge, moves, it leaves a Hole in its place. There doesn't seem to be anything concrete there - hence the name Hole - but that "absence of electron" behaves in many ways as if it were a particle.

However, unlike an electron, which can also be seen outside a crystal, the Hole exists only in conjunction with the other particles. It is for these and others thinhs that it is interpreted as a quasiparticle.

But there are more complex quasiparticles, such as excitons , that play a central role in semiconductor physics , at the basis of the functioning of various hardware components. Exciton is a bonded state of an electron and a Hole, which is created when light hits a material. Instead of the electron and the Hole annihilating, they form a bond, and that bonded state is a quasiparticle.


Sketch of the physical processes (top) and Feynman diagrams (bottom) behind an exciton (left) and a  π -ton (right). The yellow wiggled line symbolizes the incoming (and outgoing) photon, which creates an electron-hole pair denoted by open and filled circles, respectively. The Coulomb interaction between the particles is symbolized by a red wiggled line; dashed line indicates the recombination of the particle and hole; dotted line denotes the creation of a second particle-hole pair (right); black lines the underlying band structure (top panels).


Pi-ton

Anna and her colleagues Petra Pudleiner and Katharina Astleithner were just studying the excitons when they realized that their calculations were showing something much broader than expected: electrons and Holes don't have to bond just in pairs.

In fact, the calculations showed the possibility that two electrons could bind to two Holes, forming an unprecedented quasiparticle: they called it Pi-ton, or Π-ton.

"The name pi-ton comes from the fact that the two electrons and the two Holes are held together by charge density fluctuations or spin fluctuations that always invert their character 180 degrees from one point in the crystalline network to the next - or that is, by an angle of pi, measured in radians, "said Anna.

"This constant shift from more to less can be imagined as a shift from black to white on a chessboard," illustrated Petra.

Like exonium, pi-ton is created spontaneously when the material absorbs a photon. When the quasiparticle falls apart, a photon is emitted again.



"Although we are constantly surrounded by countless quasiparticles, the discovery of a new species of quasiparticle is something very special. In addition to exxciton, now there is also pi-ton. Anyway, this contributes to a better understanding of the coupling between light and solids. , a topic that plays an important role not only in basic research, but also in many technical applications - from semiconductor technology to photovoltaic energy," said Professor Karsten Held.


Bibliography:

Article: Generic Optical Excitations of Correlated Systems: π-tons

Authors: Anna Kauch, Petra Pudleiner, Katharina Astleithner, P. Thunström, T. Ribic, Karsten Held

Magazine: Physical Review Letters

Vol .: 124, 047401

DOI: 10.1103 / PhysRevLett.124.047401

Wednesday, 18 December 2019

Smart contact lens recharges wirelessly without removing it from user's eye


Electronic Contact Lenses

The robotic contact lenses have promised true superpowers to humans, the vision of laser beams to a telescopic zoom built into the eye.

This technology, still in the developmental stage, has now received a huge boost: a wireless rechargeable power source, meaning all equipment installed on the contact lens can be fueled and continue working without even being removed from the user's eye.



Instead of a traditional battery, Jihun Park and colleagues at Yonsei University in South Korea used a printable supercapacitor, making it easy to attach to the contact lens.

In addition to the rechargeable supercapacitor, the prototype has an antenna and a red LED, all working without obscuring the user's vision. It sounds like science fiction, but the device has already been tested by a volunteer and worked perfectly.

Wireless rechargeable supercapacitor scheme.

Rechargeable supercapacitor

The supercapacitor is made of carbon electrodes and a solid state polymer electrolyte. Each material is dispersed in a solvent and printed as separate layers on the lens. A high-precision technique called microscale direct ink writing allows the supercapacitor to be printed outside the area covering the user's pupil, meaning that the device does not interfere with vision.

The flexible wireless power transfer unit - comprising an ultra-thin rectifier circuit and an antenna made of nanofibers and silver nanowires - allows the contact lens to recharge at a distance of about 1 cm from a transmitting coil.



The rechargeable contact lens was tested on live rabbits and finally on a human - during the 10 minute test, no damage was detected in the volunteer's eye.


Bibliography:

Article: Printing of wirelessly rechargeable solid-state supercapacitors for soft, smart contact lenses with continuous operations

Authors: Jihun Park, David B. Ahn, Joohee Kim, Byeong-Soo Bae, Sang-Young Lee, Jang-Ung Park

Magazine: Science Advances

Vol .: 5, no. 12, eaay0764
DOI: 10.1126 / sciadv.aay0764