Can a new technique for capturing ‘hot’ electrons make solar cells more efficient?

A scanning tunnelling microscope is used to study the dynamics of hot electrons through single molecule manipulation.
Photo Credit: Adrian Hooper

A new way of extracting quantitative information from state-of-the-art single molecule experiments has been developed by physicists at the University of Bath. Using this quantitative information, the researchers will be able to probe the ultra-fast physics of ‘hot’ electrons on surfaces – the same physics that governs and limits the efficacy of silicon-based solar cells.

Solar cells work by converting light into electrons, whose energy can be collected and harvested. A hot solar cell is a novel type of cell that converts sunlight to electricity more efficiently than conventional solar cells. However, the efficiency of this process is limited by the creation of energetic, or ‘hot’, electrons that are extremely short lived and lose most of their energy to their surrounding within the first few femtoseconds of their creation (1 femtosecond equals 1/1,000,000,000,000,000 of a second).

The ultra-short lifetime of hot electrons and the corresponding short distance they can travel mean probing and influencing the properties of hot electrons is experimentally challenging. To date, there have been a few techniques capable of circumventing these challenges, but none has proven capable of spatial resolution – meaning, they can’t tell us about the crucial connection between a material’s atomic structure and the dynamics of hot electrons within that material.

Short gamma-ray bursts traced farther into distant universe

Credit: W. M. Keck Observatory/Adam Makarenko

A Northwestern University-led team of astronomers has developed the most extensive inventory to date of the galaxies where short gamma-ray bursts (SGRBs) originate.

Using several highly sensitive instruments and sophisticated galaxy modeling, the researchers pinpointed the galactic homes of 84 SGRBs and probed the characteristics of 69 of the identified host galaxies. Among their findings, they discovered that about 85% of the studied SGRBs come from young, actively star-forming galaxies.

The astronomers also found that more SGRBs occurred at earlier times, when the universe was much younger — and with greater distances from their host galaxies’ centers — than previously known. Surprisingly, several SGRBs were spotted far outside their host galaxies — as if they were “kicked out,” a finding that raises questions as to how they were able to travel so far away.

“This is the largest catalog of SGRB host galaxies to ever exist, so we expect it to be the gold standard for many years to come,” said Anya Nugent, a Northwestern graduate student who led the study focused on modeling host galaxies. “Building this catalog and finally having enough host galaxies to see patterns and draw significant conclusions is exactly what the field needed to push our understanding of these fantastic events and what happens to stars after they die.”

A possible game changer for next generation microelectronics

Magnetic fields created by skyrmions in two-dimensional sheet of material composed of iron, germanium and tellurium.
Image Credit: Argonne National Laboratory.

Magnets generate invisible fields that attract certain materials. A common example is fridge magnets. Far more important to our everyday lives, magnets also can store data in computers. Exploiting the direction of the magnetic field (say, up or down), microscopic bar magnets each can store one bit of memory as a zero or a one — the language of computers.

Scientists at the U.S. Department of Energy’s (DOE) Argonne National Laboratory wants to replace the bar magnets with tiny magnetic vortices. As tiny as billionths of a meter, these vortices are called skyrmions, which form in certain magnetic materials. They could one day usher in a new generation of microelectronics for memory storage in high performance computers.

“We estimate the skyrmion energy efficiency could be 100 to 1000 times better than current memory in the high-performance computers used in research.” — Arthur McCray, Northwestern University graduate student working in Argonne’s Materials Science Division

“The bar magnets in computer memory are like shoelaces tied with a single knot; it takes almost no energy to undo them,” said Arthur McCray, a Northwestern University graduate student working in Argonne’s Materials Science Division (MSD). And any bar magnets malfunctioning due to some disruption will affect the others.

New quantum tool developed in groundbreaking experimental achievement

SFLORG Stock Photo

For the first time in experimental history, researchers at the Institute for Quantum Computing (IQC) have created a device that generates twisted neutrons with well-defined orbital angular momentum. Previously considered an impossibility, this groundbreaking scientific accomplishment provides a brand-new avenue for researchers to study the development of next-generation quantum materials with applications ranging from quantum computing to identifying and solving new problems in fundamental physics.

“Neutrons are a powerful probe for the characterization of emerging quantum materials because they have several unique features,” said Dr. Dusan Sarenac, research associate with IQC and technical lead, Transformative Quantum Technologies at the University of Waterloo. “They have nanometer-sized wavelengths, electrical neutrality, and a relatively large mass. These features mean neutrons can pass through materials that X-rays and light cannot.”

While methods for the experimental production and analysis of orbital angular momentum in photons and electrons are well-studied, a device design using neutrons has never been demonstrated until now. Because of their distinct characteristics, the researchers had to construct new devices and create novel methods for working with neutrons.

How does radiation travel through dense plasma?

A NASA image of plasma bursting from the sun. Plasma—a hot soup of atoms with free moving electrons and ions—is the most abundant form of matter in the universe, found throughout our solar system in the sun and other planetary bodies. A new study from University of Rochester researchers provides experimental data about how radiation travels through dense plasmas, which will help scientists to better understand planetary science and fusion energy.
Credit: NASA

First-of-its-kind experimental evidence defies conventional theories about how plasmas emit or absorb radiation.

Most people are familiar with solids, liquids, and gases as three states of matter. However, a fourth state of matter, called plasmas, is the most abundant form of matter in the universe, found throughout our solar system in the sun and other planetary bodies. Because dense plasma—a hot soup of atoms with free-moving electrons and ions—typically only forms under extreme pressure and temperatures, scientists are still working to comprehend the fundamentals of this state of matter. Understanding how atoms react under extreme pressure conditions—a field known as high-energy-density physics (HEDP)—gives scientists valuable insights into the fields of planetary science, astrophysics, and fusion energy.

One important question in the field of HEDP is how plasmas emit or absorb radiation. Current models depicting radiation transport in dense plasmas are heavily based on theory rather than experimental evidence.

“This work reveals fundamental steps for rewriting current textbook descriptions of how radiation generation and transport occurs in dense plasmas.”

Scientists closer to solving a superconducting puzzle with applications in medicine, transport and power transmission

Particle accelerator
Source: University of Bristol

Researchers studying the magnetic behavior of a cuprate superconductor may have explained some of the unusual properties of their conduction electrons.

Cuprate superconductors are used in levitating trains, quantum computing and power transmission. They are of a family of materials made of layers of copper oxides alternating with layers of other metal oxides, which act as charge reservoirs.

The largest use of superconductors is currently for manufacturing superconducting magnets used for medical MRI machines and for scientific applications such as particle accelerators.

For the potential applications of superconducting materials to be fully realized, developing superconductors that maintain their properties at higher temperatures is crucial for scientists. The cuprate superconductors currently exhibit relatively high transition point temperatures and therefore give scientists an opportunity to study what makes higher temperature superconductivity possible.

New discoveries made about a promising solar cell material, thanks to new microscope

Visualization of the microscope tip exposing material to terahertz light. The colors on the material represent the light-scattering data, and the red and blue lines represent the terahertz waves.
Illustration Credit: Ames National Laboratory

A team of scientists from the Department of Energy’s Ames National Laboratory developed a new characterization tool that allowed them to gain unique insight into a possible alternative material for solar cells. Under the leadership of Jigang Wang, senior scientist from Ames Lab, the team developed a microscope that uses terahertz waves to collect data on material samples. The team then used their microscope to explore Methylammonium Lead Iodide (MAPbI3) perovskite, a material that could potentially replace silicon in solar cells.

Richard Kim, a scientist from Ames Lab, explained the two features that make the new scanning probe microscope unique. First, the microscope uses the terahertz range of electromagnetic frequencies to collect data on materials. This range is far below the visible light spectrum, falling between the infrared and microwave frequencies. Secondly, the terahertz light is shined through a sharp metallic tip that enhances the microscope’s capabilities toward nanometer length scales.

“Normally if you have a light wave, you cannot see things smaller than the wavelength of the light you're using. And for this terahertz light, the wavelength is about a millimeter, so it’s quite large,” explained Kim. “But here we used this sharp metallic tip with an apex that is sharpened to a 20-nanometer radius curvature, and this acts as our antenna to see things smaller than the wavelength that we were using.”

Cosmic chocolate pralines: general neutron star structure revealed

The study of the sound speed has revealed that heavy neutron stars have a stiff mantle and a soft core, while light neutron stars have a soft mantle and a stiff core – much like different chocolate pralines Illustration Credit: P. Kiefer/L. Rezzolla

Through extensive model calculations, physicists at Goethe University Frankfurt have reached general conclusions about the internal structure of neutron stars, where matter reaches enormous densities: depending on their mass, the stars can have a core that is either very stiff or very soft. The findings were published simultaneously in two articles today in The Astrophysical Journal Letters.

So far, little is known about the interior of neutron stars, those extremely compact objects that can form after the death of a star: the mass of our sun or even more is compressed into a sphere with the diameter of a large city. Since their discovery more than 60 years ago, scientists have been trying to decipher their structure. The greatest challenge is to simulate the extreme conditions inside neutron stars, as they can hardly be recreated on Earth in the laboratory. There are therefore many models in which various properties – from density and temperature – are described with the help of so-called equations of state. These equations attempt to describe the structure of neutron stars from the stellar surface to the inner core.

Unimon - A new qubit to boost quantum computers for useful applications

Artistic impression of a unimon qubit in a quantum processor.
Illustration Credit: Aleksandr Kakinen.

A group of scientists from Aalto University, IQM Quantum Computers, and VTT Technical Research Centre of Finland have discovered a new superconducting qubit, the unimon, to increase the accuracy of quantum computations

A group of scientists from Aalto University, IQM Quantum Computers, and VTT Technical Research Centre have discovered a new superconducting qubit, the unimon, to increase the accuracy of quantum computations. The team has achieved the first quantum logic gates with unimons at 99.9% fidelity — a major milestone on the quest to build commercially useful quantum computers. This pivotal piece of research was just published in the journal Nature Communications.

Of all the different approaches to building useful quantum computers, superconducting qubits are on the lead. However, the qubit designs and techniques currently used do not yet provide high enough performance for practical applications. In this noisy intermediate-scale quantum (NISQ) era, the complexity of the implementable quantum computations is mostly limited by errors in single- and two-qubit quantum gates. The quantum computations need to become more accurate to be useful.

FRIB Experiment Pushes Elements to the Limit

A multi-institutional team of scientific users have published the results of the first scientific experiment at the Facility for Rare Isotope Beams in the journal Physical Review Letters. The experiment studied the decay of isotopes so unstable that they only exist for fractions of a second. To perform the study, the rare isotopes were implanted into the center of a sensitive detector known as the FRIB Decay Station initiator.
Photo Credit: Facility for Rare Isotope Beams

A new study led by the Department of Energy’s Lawrence Berkeley National Laboratory (Berkeley Lab) has measured how long it takes for several kinds of exotic nuclei to decay. The paper, published today in Physical Review Letters, marks the first experimental result from the Facility for Rare Isotope Beams (FRIB), a DOE Office of Science user facility operated by Michigan State University.

Scientists used the one-of-a-kind facility to better understand nuclei, the collection of protons and neutrons found at the heart of atoms. Understanding these basic building blocks allows scientists to refine their best models and has applications in medicine, national security, and industry.

“The breadth of the facility and the programs that are being pursued are really exciting to watch,” said Heather Crawford, a physicist at Berkeley Lab and lead spokesperson for the first FRIB experiment. “Research is going to be coming out in different areas that will impact things we haven’t even thought of yet. There’s so much discovery potential.”

The first experiment is just a small taste of what’s to come at the facility, which will become 400 times more powerful over the coming years. “It’s going to be really exciting – mind-blowing, honestly,” Crawford said.

Synthetic black holes radiate like real ones

To make a synthetic black hole, just take a chain of atoms (green), and change how easy it is for an electron to jump between each atomic site, represented here by the color and width of the blue interatomic bonds. The varied bond strength in the lower chain mimics the warping of spacetime in the presence of a black hole. This way, the incredible physics of black holes can be explored in a lab on Earth.
Source/Credit:  Universiteit van Amsterdam

Black holes are the most extreme objects in the universe, packing so much mass into so little space that nothing – not even light – can escape their gravitational pull once it gets close enough.

Understanding black holes is key to unraveling the most fundamental laws governing the cosmos, because they represent the limits of two of the best-tested theories of physics: the theory of general relativity, which describes gravity as resulting from the (large-scale) warping of spacetime by massive objects, and the theory of quantum mechanics, which describes physics at the smallest length scales. To fully describe black holes, we would need to stitch these two theories together and form a theory of quantum gravity.

Radiating black holes

To achieve this goal, we might want to look at what manages to escape from black holes, rather than what gets swallowed. The event horizon is an intangible boundary around each black hole, beyond which there is no way of getting out. However, Stephen Hawking famously discovered that every black hole must emit a small amount of thermal radiation due to small quantum fluctuations around its horizon.

Searching for traces of dark matter with neutron spin clocks

Part of the experimental apparatus in the laboratory in Bern with PhD student Ivo Schulthess.
Credit: zvg/mad/Courtesy of F. Piegsa

With the use of a precision experiment developed at the University of Bern, an international research team has succeeded in significantly narrowing the scope for the existence of dark matter. The experiment was carried out at the European Research Neutron Source at the Institute Laue-Langevin in France, and makes an important contribution to the search for these particles, of which little remains known.

Cosmological observations of the orbits of stars and galaxies enable clear conclusions to be drawn about the attractive gravitational forces that act between the celestial bodies. The astonishing finding: visible matter is far from sufficient for being able to explain the development or movements of galaxies. This suggests that there exists another, so far unknown, type of matter. Accordingly, in the year 1933, the Swiss physicist and astronomer Fritz Zwicky inferred the existence of what is known now as dark matter. Dark matter is a postulated form of matter which isn’t directly visible but interacts via gravity, and consists of approximately five times more mass than the matter with which we are familiar.

Recently, following a precision experiment developed at the Albert Einstein Center for Fundamental Physics (AEC) at the University of Bern, an international research team succeeded in significantly narrowing the scope for the existence of dark matter. With more than 100 members, the AEC is one of the leading international research organizations in the field of particle physics. The findings of the team, led by Bern, have now been published in the highly-regarded journal Physical Review Letters.

New quantum phase discovered for developing hybrid materials

 Metropolitan University Scientists have discovered that in Ba1-xSrxAl2O4, a highly disordered atomic arrangement is formed in the AlO4 network at chemical compositions near the structural quantum critical point, resulting in both characteristics of crystalline and amorphous materials.
Illustration Credit: Yui Ishii, Osaka

Scientists discovered a hybrid state in which crystals exhibit both crystalline and amorphous characteristics near the structural quantum critical point.

If you have ever watched water freeze to ice, you have witnessed what physicists call a “phase transition.” Osaka Metropolitan University scientists have discovered an unprecedented phase transition during which crystals achieve amorphous characteristics while retaining their crystalline properties. Their findings contribute to developing hybrid materials for use in harsh environments, such as outer space. The results were published in Physical Review B.

A typical phase transition exhibited by crystalline solids involves a change in the crystal structure. Such structural phase transitions usually occur at finite temperatures. However, controlling the chemical composition of the crystal can lower the transition temperature to absolute zero (−273°C). The transition point at absolute zero is called the structural quantum critical point.

Zero Gravity Helps Create Homogeneous Material Structure

The mathematical model of the UrFU scientists helps to simulate the solidification process of an alloy. Credit: unsplash.com / Dan Cristian Pădureț

In space, due to the absence of gravity, metal hardens more homogeneously than on Earth. This was discovered by physicists who calculated the solidification process of aluminum-nickel metal alloys. Alloys were not chosen by chance, as they are one of the most common and account for 20% of all metalworking in the world. The model was built based on experimental data: the results obtained for alloy samples in microgravity on board the International Space Station were compared with the results of samples processed in terrestrial conditions. The results of experiments and modeling are presented in the journal Acta Materialia.

All aluminum-based materials are produced from the liquid phase, which is the initial phase. The solidification process and the conditions present at the moment of solidification determine the microstructural state of the final part, the scientists explain. The model considers the effects of crystallization rate and supercooling on the formation of alloy structure and properties, and allows the correct prediction of the microstructure and the required mechanical and electrical properties of the alloy.

Designing Next-Generation Metals, One Atom at a Time

Pacific Northwest National Laboratory researchers are visualizing how shear forces rearrange metal atoms in ways that translate to improved characteristics—like greater strength, ductility, and conductivity—to inform the custom design of next-generation metals with broad applications from batteries to vehicles.   
Composite Credit: image by Shannon Colson | Pacific Northwest National Laboratory

How can studying metals manufacturing lead to longer-lasting batteries and lighter vehicles? It all comes down to physics.

Researchers at Pacific Northwest National Laboratory (PNNL) are investigating the effects of physical forces on metals by taking a direct look at atomic-level changes in metals undergoing shear deformation.

The forces applied during shear deformation to change a metal’s shape also rearrange its atoms, but not in the same way for every metal or alloy. Atomic arrangement can affect metal properties like strength, formability, and conductivity—so better understanding how atoms move during shear is a key part of ongoing efforts to custom design next-generation metals with specific properties from the atom up.

Scientists discover exotic quantum state at room temperature

Researchers at Princeton discovered a material, made from the elements bismuth and bromine, that allows specialized quantum behaviors — usually seen only under high pressures and temperatures near absolute zero — to appear at room temperature. 
Photo Credit: Shafayat Hossain and M. Zahid Hasan, Princeton University

For the first time, physicists have observed novel quantum effects in a topological insulator at room temperature. This finding opens up a new range of possibilities for the development of efficient quantum technologies, such as spin-based electronics, which may potentially replace many current electronic systems for higher energy efficiency.

The breakthrough, published as the cover article of the October issue of Nature Materials, came when Princeton scientists explored a topological material based on the element bismuth.

The scientists have used topological insulators to demonstrate quantum effects for more than a decade, but this experiment is the first time these effects have been observed at room temperature. Typically, inducing and observing quantum states in topological insulators requires temperatures around absolute zero, which is equal to minus 459 degrees Fahrenheit (or -273 degrees Celsius).

In recent years, the study of topological states of matter has attracted considerable attention among physicists and engineers and is presently the focus of much international interest and research. This area of study combines quantum physics with topology — a branch of theoretical mathematics that explores geometric properties that can be deformed but not intrinsically changed.

“The novel topological properties of matter have emerged as one of the most sought-after treasures in modern physics, both from a fundamental physics point of view and for finding potential applications in next-generation quantum engineering and nanotechnologies,” said M. Zahid Hasan, the Eugene Higgins Professor of Physics at Princeton University, led the research. “This work was enabled by multiple innovative experimental advances in our lab at Princeton.”

Polarized X-Rays Reveal Shape, Orientation of Extremely Hot Matter Around Black Hole

An artist’s impression of the Cygnus X-1 system, with the black hole appearing in the center and its companion star on the left. New measurements from Cygnus X-1, reported Nov. 3 in the journal Science, represent the first observations of a mass-accreting black hole from the Imaging X-Ray Polarimetry Explorer (IXPE) mission, an international collaboration between NASA and the Italian Space Agency.
Illustration Credit: John Paice

Researchers’ recent observations of a stellar-mass black hole called Cygnus X-1 reveal new details about the configuration of extremely hot matter in the region immediately surrounding the black hole.

Matter is heated to millions of degrees as it is pulled toward a black hole. This hot matter glows in X-rays. Researchers are using measurements of the polarization of these X-rays to test and refine models that describe how black holes swallow matter, becoming some of the most luminous sources of light — including X-rays — in the universe.

The new measurements from Cygnus X-1, reported Nov. 3 in the journal Science, represent the first observations of a mass-accreting black hole from the Imaging X-Ray Polarimetry Explorer (IXPE) mission, an international collaboration between NASA and the Italian Space Agency (ASI). Cygnus X-1 is one of the brightest X-ray sources in our galaxy, consisting of a 21 solar mass black hole in orbit with a 41 solar mass companion star.

Method to char­ac­ter­ize large quan­tum com­put­ers

View inside an ion trap, the heart of an ion trap quantum computer. 
Credit: C Lackner/Quantum Optics and Spectroscopy Group, University of Innsbruck

Quantum devices are becoming ever more complex and powerful. Researchers at the University of Innsbruck, in collaboration with the Johannes Kepler University Linz and the University of Technology Sydney, are now presenting a method to characterize even large quantum computers using only a single measurement setting.

The gold-standard for the characterization of quantum devices is so-called quantum tomography, which in analogy to medical tomography, can draw a complete picture of a quantum system from a series of snapshots of the system. While offering plenty of insights, the number of measurements required for tomography increases rapidly, with three times as many measurements required for every additional qubit. Due to the sheer time it takes to perform all these measurements, tomography has only been possible on devices with a handful of qubits. However, recent developments on quantum computers have successfully scaled up system sizes much beyond the capabilities of tomography, making their characterization a daunting bottleneck.

As dense as it gets: New Model for Matter in Neutron Star Collisions

Illustration of the new method: the researchers use five-dimensional black holes (right) to calculate the phase diagram of strongly coupled matter (middle), enabling simulations of neutron star mergers and the produced gravitational waves (left).
Source/Credit: Goethe University

With the exception of black holes, neutron stars are the densest objects in our universe. As their name suggests, neutron stars are mainly made of neutrons. However, our knowledge about the matter produced during the collision of two neutron stars is still limited. Scientists from Goethe University Frankfurt and the Asia Pacific Center for Theoretical Physics in Pohang have now developed a new model that gives insights about matter under such extreme conditions.

After a massive star has burned its fuel and explodes as a supernova, an extremely compact object, called a neutron star, can be formed. Neutron stars are extraordinarily dense: To reach the density inside them, one would need to squeeze a massive body like our sun down to the size of a city like Frankfurt. In 2017, gravitational waves, the small ripples in spacetime that are produced during a collision of two neutron stars, could be directly measured here on earth for the first time. However, the composition of the resulting hot and dense merger product is not known precisely. It is still an open question, for instance, whether quarks, which are otherwise trapped in neutrons, can appear in free form after the collision. Dr. Christian Ecker from the Institute for Theoretical Physics of Goethe University Frankfurt, Germany, and Dr. Matti Järvinen and Dr. Tuna Demircik from the Asia Pacific Center for Theoretical Physics in Pohang, South Korea, have now developed a new model that allows them to get one step closer to answering this question.

Physicists Proposed Theory of Solidification of Nickel and Iron Alloys

Nickel-iron alloy is used when high dimensional stability of finished parts is required.
Photo: unsplash.com / Laura Ockel

Physicists at Ural Federal University have created a theory for the solidification of a nickel-iron alloy (invar). They determined that an important role in the technology of creating products from invar, namely in the solidification process, is played by the oncoming flow: when the alloy cools, the liquid layer flows on top of the solidified layer. If you regulate this process, you can control the characteristics of the alloys, obtain a more homogeneous structure, thereby improving the properties of the final product.

The work of scientists is extremely important because nickel and iron alloys are used in creating high-precision devices: clocks, seismic sensors, substrates for chips, valves and engines in aircraft structures, and instruments for telescopes. The calculations will help to create an alloy with the desired structure, which will affect the quality of the finished products. Description of the model and behavior of melts, as well as analytical calculations, scientists have published in the journal Scientific Reports. The research was supported by the Russian Science Foundation (Project No. 21-79-10012).

"Let me explain the work with an analogy. When water freezes, it pushes out all the dirt. So, you can put a piece of ice in your mouth, it will be clean. This is roughly what happens to melts when they cool. The only difference is that they do not push out all the impurities, but some of them. Some of the impurities leak out, and some of the impurities stay in the melt. What remains in the melt fills the gaps between the crystals, which solidify, and the voids, which remain. As a result, the alloys are heterogeneous: one tiny piece is enriched and the neighboring piece is not. This affects the properties of the finished product," says Dmitry Aleksandrov, Head of the Ural Federal University's Laboratory of Multi-Scale Mathematical Modeling.