Lifeboat Foundation

Light travels at a speed of about 300, 000, 000 meters per second as light particles, photons, or equivalently as electromagnetic field waves. Experiments led by Hrvoje Petek, an R.K. Mellon professor in the Department of Physics and Astronomy examined ideas surrounding the origins of light, taking snapshots of light, stopping light and using it to change properties of matter.

Petek worked with students and collaborators Prof. Chen-Bin (Robin) Huang of the National Tsing Hua University in Taiwan, and Atsushi Kubo of the Tsukuba University of Japan on the experiments. Their findings were reported in the paper, “Plasmonic topological quasiparticle on the nanometre and femtosecond scales,” which was published in the Dec. 24 issue of Nature magazine.

Petek credited graduate student Yanan Dai for his foresight and work in the process.

On the electromagnetic spectrum, terahertz light is located between infrared radiation and microwaves. It holds enormous potential for tomorrow’s technologies: Among other things, it might succeed 5G by enabling extremely fast mobile communications connections and wireless networks. The bottleneck in the transition from gigahertz to terahertz frequencies has been caused by insufficiently efficient sources and converters. A German-Spanish research team with the participation of the Helmholtz-Zentrum Dresden-Rossendorf (HZDR) has now developed a material system to generate terahertz pulses much more effectively than before. It is based on graphene, i.e., a super-thin carbon sheet, coated with a metallic lamellar structure. The research group presented its results in the journal ACS Nano.

Some time ago, a team of experts working on the HZDR accelerator ELBE were able to show that graphene can act as a frequency multiplier: When the two-dimensional carbon is irradiated with light pulses in the low terahertz frequency range, these are converted to higher frequencies. Until now, the problem has been that extremely strong input signals, which in turn could only be produced by a full-scale particle accelerator, were required to generate such terahertz pulses efficiently.“This is obviously impractical for future technical applications,” explains the study’s primary author Jan-Christoph Deinert of the Institute of Radiation Physics at HZDR. “So, we looked for a material system that also works with a much less violent input, i.e., with lower field strengths.”

For this purpose, HZDR scientists, together with colleagues from the Catalan Institute of Nanoscience and Nanotechnology (ICN2), the Institute of Photonic Sciences (ICFO), the University of Bielefeld, TU Berlin and the Mainz-based Max Planck Institute for Polymer Research, came up with a new idea: the frequency conversion could be enhanced enormously by coating the graphene with tiny gold lamellae, which possess a fascinating property: “They act like antennas that significantly amplify the incoming terahertz radiation in graphene,” explains project coordinator Klaas-Jan Tielrooij from ICN2. “As a result, we get very strong fields where the graphene is exposed between the lamellae. This allows us to generate terahertz pulses very efficiently.”

An especially counter-intuitive feature of quantum mechanics is that a single event can exist in a state of superposition—happening both here and there, or both today and tomorrow.

Such superpositions are hard to create, as they are destroyed if any kind of information about the place and time of the event leaks into the surrounding—and even if nobody actually records this information. But when superpositions do occur, they lead to observations that are very different from that of classical physics, raising questions that spill over into our very understanding of space and time.

Scientists from EPFL, MIT, and CEA Saclay, publishing in Science Advances, demonstrate a state of vibration that exists simultaneously at two different times, and provide evidence of this quantum superposition by measuring the strongest class of quantum correlations between light beams that interact with the vibration.

A team of scientists at Freie Universität Berlin has developed an artificial intelligence (AI) method for calculating the ground state of the Schrödinger equation in quantum chemistry. The goal of quantum chemistry is to predict chemical and physical properties of molecules based solely on the arrangement of their atoms in space, avoiding the need for resource-intensive and time-consuming laboratory experiments. In principle, this can be achieved by solving the Schrödinger equation, but in practice this is extremely difficult.

Up to now, it has been impossible to find an exact solution for arbitrary molecules that can be efficiently computed. But the team at Freie Universität has developed a deep learning method that can achieve an unprecedented combination of accuracy and computational efficiency. AI has transformed many technological and scientific areas, from computer vision to materials science. “We believe that our approach may significantly impact the future of quantum chemistry,” says Professor Frank Noé, who led the team effort. The results were published in the reputed journal Nature Chemistry.

Central to both quantum chemistry and the Schrödinger equation is the wave function —a mathematical object that completely specifies the behavior of the electrons in a molecule. The wave function is a high-dimensional entity, and it is therefore extremely difficult to capture all the nuances that encode how the individual electrons affect each other. Many methods of quantum chemistry in fact give up on expressing the wave function altogether, instead attempting only to determine the energy of a given molecule. This however requires approximations to be made, limiting the prediction quality of such methods.

Hydrogen is a sustainable source of clean energy that avoids toxic emissions and can add value to multiple sectors in the economy including transportation, power generation, metals manufacturing, among others. Technologies for storing and transporting hydrogen bridge the gap between sustainable energy production and fuel use, and therefore are an essential component of a viable hydrogen economy. But traditional means of storage and transportation are expensive and susceptible to contamination. As a result, researchers are searching for alternative techniques that are reliable, low-cost and simple. More-efficient hydrogen delivery systems would benefit many applications such as stationary power, portable power, and mobile vehicle industries.

Now, as reported in the journal Proceedings of the National Academy of Sciences, researchers have designed and synthesized an effective material for speeding up one of the limiting steps in extracting hydrogen from alcohols. The material, a catalyst, is made from tiny clusters of nickel metal anchored on a 2-D substrate. The team led by researchers at Lawrence Berkeley National Laboratory’s (Berkeley Lab) Molecular Foundry found that the catalyst could cleanly and efficiently accelerate the reaction that removes hydrogen atoms from a liquid chemical carrier. The material is robust and made from earth-abundant metals rather than existing options made from precious metals, and will help make hydrogen a viable energy source for a wide range of applications.

“We present here not merely a catalyst with higher activity than other nickel catalysts that we tested, for an important renewable energy fuel, but also a broader strategy toward using affordable metals in a broad range of reactions,” said Jeff Urban, the Inorganic Nanostructures Facility director at the Molecular Foundry who led the work. The research is part of the Hydrogen Materials Advanced Research Consortium (HyMARC), a consortium funded by the U.S. Department of Energy’s Office of Energy Efficiency and Renewable Energy Hydrogen and Fuel Cell Technologies Office (EERE). Through this effort, five national laboratories work towards the goal to address the scientific gaps blocking the advancement of solid hydrogen storage materials. Outputs from this work will directly feed into EERE’s H2@Scale vision for affordable hydrogen production, storage, distribution and utilization across multiple sectors in the economy.

Electronics are increasingly being paired with optical systems, such as when accessing the internet on an electronically run computer through fiber optic cables.

But meshing optics — which relies on particles of light called photons—with electronics—relying on electrons — is challenging, due to their disparate scales. Electrons work at a much smaller scale than light does. The mismatch between electronic systems and optical systems means that every time a signal converts from one to the other, inefficiency creeps into the system.

Now, a team led by a Purdue University scientist has found a way to create more efficient metamaterials using semiconductors and a novel aspect of physics that amplifies the activity of electrons. The study is published in the journal Optica.

A team of researchers from MIT and several institutions in Korea has found that the speed of magnetic domain wall movement is fundamentally limited. In their paper published in the journal Science, the group describes testing a theory regarding the maximum speed of domain walls to prove them correct. Matthew Daniels and Mark Stiles with the National Institute of Standards and Technology in the U.S. have published a Perspective piece outlining the work by the researchers in the same journal issue and sum up the implications of their findings.

One of the basic tenets of Einstein’s theory of special relativity is that there is no particle that can travel faster than the speed of light. In this new effort, the researchers have found a similar boundary for magnetic domain walls.

Materials that are magnetic have domains in which ordered spins are separated from one another by boundaries known as domain walls. Prior research has shown that such walls can be moved by applying an electric current. This particular aspect of magnetic materials has formed the basis of research on racetrack memory. And because the speed of movement of the domain walls determines the speed of the memories created using them, scientists have been pushing them faster and faster. Logic suggests that there must be a limit to how fast the domain walls can be pushed, however, thus establishing a limit to how fast such memories can operate. In this new effort, the researchers have found that fundamental limit.

How do molecular catalysts—molecules which, like enzymes, can trigger or accelerate certain chemical reactions—function, and what effects do they have? A team of chemists at the University of Oldenburg has come closer to the answers using a model molecule that functions like a molecular nanobattery. It consists of several titanium centers linked to each other by a single layer of interconnected carbon and nitrogen atoms. The seven-member research team recently published its findings, which combine the results of three multi-year Ph.D. research projects, in ChemPhysChem. The physical chemistry and chemical physics journal featured the basic research from Oldenburg on its cover.

To gain a better understanding of how the molecule works, the researchers, headed by first authors Dr. Aleksandra Markovic and Luca Gerhards and corresponding author Prof. Dr. Gunther Wittstock, performed electrochemical and spectroscopic experiments and used the university’s high-performance computing cluster for their calculations. Wittstock sees the publication of the paper as a “success story” for both the Research Training Groups within which the Ph.D. projects were conducted and for the university’s computing cluster. “Without the high-performance computing infrastructure, we would not have been able to perform the extensive calculations required to decipher the behavior of the molecule,” says Wittstock. “This underlines the importance of such computing clusters for current research.”

In the paper, the authors present the results of their analysis of a molecular structure, the prototype for which was the result of an unexpected chemical reaction first reported by the University of Oldenburg’s Chemistry Department in 2006. It is a highly complex molecular structure in which three titanium centers (commonly referred to in high school lessons as titanium ions) are connected to each other by a bridging ligand consisting of carbon and nitrogen. Such a compound would be expected to be able to accept and release several electrons through the exchange of electrons between the metal centers among other reasons.

The crystalline solid BaTiS₃ (barium titanium sulfide) is terrible at conducting heat, and it turns out that a wayward titanium atom that exists in two places at the same time is to blame.

The discovery, made by researchers from Caltech, USC, and the Department of Energy’s Oak Ridge National Laboratory (ORNL), was published on November 27 in the journal Nature Communications. It provides a fundamental atomic-level insight into an unusual thermal property that has been observed in several materials. The work is of particular interest to researchers who are exploring the potential use of crystalline solids with poor thermal conductivity in thermoelectric applications, in which heat is directly converted into electric energy and vice versa.

“We have found that quantum mechanical effects can play a huge role in setting the thermal transport properties of materials even under familiar conditions like room temperature,” says Austin Minnich, professor of mechanical engineering and applied physics at Caltech and co-corresponding author of the Nature Communications paper.