Scientists reveal mechanism of electron char…

Scientists reveal mechanism of electron charge exchange in molecules

Researchers at the University of California, Irvine have developed a new scanning transmission electron microscopy method that enables visualization of the electric charge density of materials at sub-angstrom resolution.

With this technique, the UCI scientists were able to observe electron distribution between atoms and molecules and uncover clues to the origins of ferroelectricity, the capacity of certain crystals to possess spontaneous electric polarization that can be switched by the application of an electric field. The research, which is highlighted in a study published today in Nature, also revealed the mechanism of charge transfer between two materials.

“This method is an advancement in electron microscopy—from detecting atoms to imaging electrons—that could help us engineer new materials with desired properties and functionalities for devices used in data storage, energy conversion and quantum computing,” said team leader Xiaoqing Pan, UCI’s Henry Samueli Endowed Chair in Engineering and a professor of both materials science & engineering and physics & astronomy.

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Physicists unlock the mystery of thermionic …

Physicists unlock the mystery of thermionic emissions in graphene

When a metal is heated to a sufficiently high temperature, electrons can be ejected out from the surface in a process known as the thermionic emission, a process that is similar to the evaporation of water molecules from the surface of boiling water.

The thermionic emission of electrons plays an important role in both fundamental physics and digital electronic technology. Historically, the discovery of thermionic emission enables physicists to produce beams of free-flowing electrons in a vacuum. Such electron beams had been used in the hallmark experiments performed by Clinton Davisson and Lester Germer in the 1920s’ to illustrate the wave-particle duality of electrons—a bizarre consequence of quantum physics, which marked the dawn of the modern quantum era. Technologically, thermionic emission forms the core of vacuum tube technology—the precursor of modern-day transistor technology—that enabled the development of the first-generation digital computer. Today, thermionic emission remains one of the most important electricity conduction mechanisms that governs the operation of billions of transistors embedded in our modern-day computers and smartphones.

Although thermionic emission in traditional materials, such as copper and silicon, has been well-explained by a theoretical model put forward by British physicist O. W. Richardson in 1901, exactly how thermionic emission takes place in graphene, a one-atom thin nanomaterials with highly unusual physical properties, remains a poorly understood problem.

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Scientists finally find superconductivity in…

Scientists finally find superconductivity in place they have been looking for decades

Researchers at Stanford University and the Department of Energy’s SLAC National Accelerator Laboratory say they have found the first, long-sought proof that a decades-old scientific model of material behavior can be used to simulate and understand high-temperature superconductivity ­- an important step toward producing and controlling this puzzling phenomenon at will.

The simulations they ran, published in Science today, suggest that researchers might be able to toggle superconductivity on and off in copper-based materials called cuprates by tweaking their chemistry so electrons hop from atom to atom in a particular pattern—as if hopping to the atom diagonally across the street rather than to the one next door.

“The big thing you want to know is how to make superconductors operate at higher temperatures and how to make superconductivity more robust,” said study co-author Thomas Devereaux, director of the Stanford Institute for Materials and Energy Sciences (SIMES) at SLAC. “It’s about finding the knobs you can turn to tip the balance in your favor.”

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Iridium ‘loses its identity’ whe…

Iridium ‘loses its identity’ when interfaced with nickel

Hey, physicists and materials scientists: You’d better reevaluate your work if you study iridium-based materials—members of the platinum family—when they are ultra-thin.

Iridium “loses its identity” and its electrons act oddly in an ultra-thin film when interfaced with nickel-based layers, which have an unexpectedly strong impact on iridium ions, according to Rutgers University-New Brunswick physicist Jak Chakhalian, senior author of a Rutgers-led study in the journal Proceedings of the National Academy of Sciences.

The scientists also discovered a new kind of magnetic state when they created super-thin artificial superstructures containing iridium and nickel, and their findings could lead to greater manipulation of quantum materials and deeper understanding of the quantum state for novel electronics.

“It seems nature has several new tricks that will force scientists to reevaluate theories on these special quantum materials because of our work,” said Chakhalian, Professor Claud Lovelace Endowed Chair in Experimental Physics in the Department of Physics and Astronomy in the School of Arts and Sciences. “Physics by analogy doesn’t work. Our findings call for the careful evaluation and reinterpretation of experiments on ‘spin-orbit physics’ and magnetism when the interfaces or surfaces of materials with platinum group atoms are involved.”

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For superconductors, discovery comes from di…

For superconductors, discovery comes from disorder

Discovered more than 100 years ago, superconductivity continues to captivate scientists who seek to develop components for highly efficient energy transmission, ultrafast electronics or quantum bits for next-generation computation. However, determining what causes substances to become—or stop being—superconductors remains a central question in finding new candidates for this special class of materials.

In potential superconductors, there may be several ways electrons can arrange themselves. Some of these reinforce the superconducting effect, while others inhibit it. In a new study, scientists at the U.S. Department of Energy’s (DOE) Argonne National Laboratory have explained the ways in which two such arrangements compete with each other and ultimately affect the temperature at which a material becomes superconducting.

In the superconducting state, electrons join together into so-called Cooper pairs, in which the motion of electrons is correlated; at each moment, the velocities of the electrons participating in a given pair are opposite. Ultimately, the motion of all electrons is coupled—no single electron can do its own thing—which leads to the lossless flow of electricity: superconductivity.

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How electrons in transition metals get redistributed

The distribution of electrons in transition metals, which represent a large part of the periodic table of chemical elements, is responsible for many of their interesting properties used in applications. The magnetic properties of some of the members of this group of materials are, for example, exploited for data storage, whereas others exhibit excellent electrical conductivity. Transition metals also have a decisive role for novel materials with more exotic behaviour that results from strong interactions between the electrons. Such materials are promising candidates for a wide range of future applications.

In their experiment, whose results they report in a paper published today in Nature Physics, Mikhail Volkov and colleagues in the Ultrafast Laser Physics group of Prof. Ursula Keller exposed thin foils of the transition metals titanium and zirconium to short laser pulses. They observed the redistribution of the electrons by recording the resulting changes in optical properties of the metals in the extreme ultraviolet (XUV) domain. In order to be able to follow the induced changes with sufficient temporal resolution, XUV pulses with a duration of only few hundred attoseconds (10^-18 s) were employed in the measurement. By comparing the experimental results with theoretical models, developed by the group of Prof. Angel Rubio at the Max Planck Institute for the Structure and Dynamics of Matter in Hamburg, the researchers established that the change unfolding in less than a femtosecond (10^-15 s) is due to a modification of the electron localization in the vicinity of the metal atoms. The theory also predicts that in transition metals with more strongly filled outer electron shells an opposite motion – that is, a delocalization of the electrons – is to be expected.

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How to trick electrons to see the hidden face …

How to trick electrons to see the hidden face of crystals: Researchers try a trick for complete 3D analysis of submicron crystals

The 3D analysis of crystal structures requires a full 3D view of the crystals. Crystals as small as powder, with edges less than one micrometer, can only be analysed with electron radiation. With electron crystallography, a full 360-degree view of a single crystal is technically impossible. A team of researchers led by Tim Gruene from the Faculty of Chemistry at the University of Vienna modified the holder of the tiny crystals so that a full view becomes possible. Now they presented their solutions in the journal „Nature Communications".

[…]

Typically, crystallographers use X-rays to examine their samples. Size, however, matters greatly for X-ray structure analysis: Crystals with edges less than 50 to 100 micrometres are too small to produce a measurable signal. “Electron crystallography is a quite recent development. We demonstrated to our chemist colleagues that we can analyse crystals with edges less than 1 micrometre – this includes many crystals which escape 3D structure determination so far”, Tim Grüne says, who is member of the Department of Inorganic Chemistry and head of the Centre for X-ray Structure Analysis.

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Experiments explore the mysteries of ‘…

Experiments explore the mysteries of ‘magic’ angle superconductors

In spring 2018, the surprising discovery of superconductivity in a new material set the scientific community abuzz. Built by layering one carbon sheet atop another and twisting the top one at a “magic” angle, the material enabled electrons to flow without resistance, a trait that could dramatically boost energy efficient power transmission and usher in a host of new technologies.

Now, new experiments conducted at Princeton give hints at how this material—known as magic-angle twisted graphene—gives rise to superconductivity. In this week’s issue of the journal Nature, Princeton researchers provide firm evidence that the superconducting behavior arises from strong interactions between electrons, yielding insights into the rules that electrons follow when superconductivity emerges.

“This is one of the hottest topics in physics,” said Ali Yazdani, the Class of 1909 Professor of Physics and senior author of the study. “This is a material that is incredibly simple, just two sheets of carbon that you stick one on top of the other, and it shows superconductivity.”

Exactly how superconductivity arises is a mystery that laboratories around the world are racing to solve. The field even has a name, “twistronics.”

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Pairing ‘glue’ for electrons in …

Pairing ‘glue’ for electrons in iron-based high-temp superconductors studied

Newly published research from a team of scientists led by the U.S. Department of Energy’s Ames Laboratory sheds more light on the nature of high-temperature iron-based superconductivity.

Current theories suggest that magnetic fluctuations play a very significant role in determining superconducting properties and even act as a “pairing glue” in iron-based superconductors.

“A metal becomes a superconductor when normal electrons form what physicists call Cooper pairs. The interactions responsible for this binding are often referred to as ‘pairing glue.’ Determining the nature of this glue is the key to understanding, optimizing and controlling superconducting materials,” said Ruslan Prozorov, an Ames Laboratory physicist who is an expert in superconductivity and magnetism.

The scientists, from Ames Laboratory, Nanjing University, University of Minnesota, and L’École Polytechnique, focused their attention on high quality single crystal samples of one widely studied family of iron-arsenide high-temperature superconductors. They sought an experimental approach to systematically disrupt the magnetic, electronic and superconducting ordered states; while keeping the magnetic field, temperature, and pressure unchanged.

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A new method to study polarons in insulators…

A new method to study polarons in insulators and semiconductors

A team of researchers at the University of Oxford have recently introduced a new way to model polarons, a quasiparticle typically used by physicists to understand interactions between electrons and atoms in solid materials. Their method, presented in a paper published in Physical Review Letters, combines theoretical modeling with computational simulations, enabling in-depth observations of these quasiparticles in a wide range of materials.

Essentially, a polaron is a composite particle comprised of an electron surrounded by a cloud of phonons (i.e. lattice vibrations). This quasiparticle is heavier than the electron itself and due to its substantial weight it can sometimes become trapped in a crystal lattice.

Polarons contribute to the electric currentthat powers several technological tools, including organic light-emitting diodes and touchscreens. Understanding their properties is thus of key importance, as it could help to develop the next generation of various devices for lighting and optoelectronics.

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