New research from the University of Birmingham shows that the electronic structure of metals can strongly affect their mechanical properties. The research, published today (26th October) in the journal Science, demonstrates experimentally, for the first time, that the electronic and mechanical properties of a metal are connected. It was previously understood theoretically that there would be a connection, but it was thought that it would be too small to detect in an experiment. Dr Clifford Hicks, Reader in Condensed Matter Physics, who worked on the study said: "Mechanical properties are typically described in terms of the bonding between atoms, while electronic properties of metals are described by states that extend across many atoms. The atomic lattice (the term used to describe the arrangement of atoms) of a metal and its mechanical properties are generally thought of as being unaffected by which electronic states are occupied and which are empty, but in this work, we show that this is not always a good assumption."

Pathbreaking Platform for Quantum Simulation: A Metal-Like Quantum Gas

Electronic properties of condensed matter are often determined by an intricate competition between kinetic energy that aims to overlap and delocalize electronic wave functions across the crystal lattice, and localizing electron-electron interactions. In contrast, the gaseous phase is characterized by valence electrons tightly localized around the ionic atom cores in discrete quantum states with well-defined energies.

As an exotic hybrid of both situations, one may wonder which state of matter is created when a gas of isolated atoms is suddenly excited to a state where electronic wave functions spatially overlap like in a solid? Such an exotic phase of matter, however, has so far been impossible to be created in principle.

Extremely Fast Electronic Changes Observed in Real Time in a Special Material Class

In physics, they are currently the subject of intensive research; in electronics, they could enable completely new functions. So-called topological materials are characterized by special electronic properties, which are also very robust against external perturbations. This material group also includes tungsten ditelluride. In this material, such a topologically protected state can be “broken up” using special laser pulses within a few trillionths of a second (“picoseconds”) and thus change its properties. This could be a key requirement for realizing extremely fast, optoelectronic switches. For the first time physicists at Kiel University (CAU), in cooperation with researchers at the Max Planck Institute for Chemical Physics of Solids (MPI-CPfS) in Dresden, Tsinghua University in Beijing and Shanghai Tech University, have been able to observe changes to the electronic properties of this material in experiments in real-time. Using laser pulses, they put the atoms in a sample of tungsten ditelluride into a state of controlled excitation, and were able to follow the resulting changes in the electronic properties “live” with high-precision measurements. They published their results recently in the scientific journal Nature Communications.

Weyl semimetals with unusual electronic properties

“If these laser-induced changes can be reversed again, we essentially have a switch that can be activated optically, and which can change between different electronic states,” explained Michael Bauer, professor of solid state physics at the CAU. Such a switching process has already been predicted by another study, in which researchers from the USA were recently able to directly observe the atomic movements in tungsten ditelluride. In their study, the physicists from the Institute of Experimental and Applied Physics at the CAU now focused on the behavior of the electrons, and how the electronic properties in the same material can be altered using laser pulses.

A material that can switch between multiple phases that have distinct electronic, optical and magnetic properties

A large team of researchers with members from China, the U.K., the U.S. and Japan has developed a material that can switch between multiple phases with distinct electronic, optical and magnetic properties. In their paper published in the journal Nature, the team describes how they made their material, how it can be caused to switch properties and possible uses for it. Shriram Ramanathan, with Purdue University offers a News & Views piece on the work done by the team in the same journal issue and adds some additional background on the search for functional materials.

As Ramanathan points out, humans have been searching for functional materials for centuries—we want more out of our materials than simply bearing loads. As he further notes, many such materials have been developed due to clearly directed efforts, but some have also come about by changing a material that has already been discovered. In this new effort, the researchers have taken the latter approach—they have modified an existing material to make it more useful by causing it to have different properties depending on how it is used.

To create the new material, the researchers created a thin layer of ceramic material in the traditional way, on top of a substrate. But instead of cooking it, as has been done historically, they covered the surface of the material with an ionic gel-like liquid. To provide for additional functionality, the liquid was an electrical insulator and able to conduct ions. It also held dissolved oxide ions and hydrogen ions. When electricity was applied to the material, the result depended on the polarity of the voltage—ions from either the hydrogen or oxide ions were driven into the ceramic material below. Reversing the voltage induced the reverse, which quite obviously meant that the system was reversible, as well.

Electrostatic design of materials: A fundamentally new approach

Collective electrostatic effects are used to intentionally manipulate material properties

Computational materials design is traditionally used to improve and further develop already existing materials. Simulations grant a deep insight into the quantum mechanical effects which determine material properties. Egbert Zojer and his team at the Institute of Solid State Physics of TU Graz go a decisive step beyond that: they use computer simulations to propose an entirely new concept for controlling the electronic properties of materials. Potentially disturbing influences arising from the regular arrangement of polar elements, so-called collective electrostatic effects, are used by the research group to intentionally manipulate material properties. That this radically new approach also works for three-dimensional materials has been demonstrated by the Graz team in Advanced Materials, which according to Google Scholar is internationally the most important journal in the field of materials research.

Manipulation of the energetic materials landscape

"The basic approach of the electrostatic design concept is to modify the electronic states of semiconductors via the periodic arrangement of dipolar groups. In this way we are able to locally manipulate energy levels in a controlled way. In doing so, we do not try to find ways to bypass such effects which are inevitable especially at interfaces. Rather, we make deliberate use of them for our own purposes," explains Egbert Zojer.

Man-made Material Shows Surprisingly Magnetic Personality

http://earthchangesmedia.com/man-made-material-shows-surprisingly-magnetic-personality

Scientists from SLAC and Stanford have used finely tuned X-rays at the Stanford Synchrotron Radiation Lightsource (SSRL) to pin down the source of a mysterious magnetism that appears when two materials are sandwiched together.

Both materials are perovskites, a class of mineral oxides whose…

Scientists from SLAC…