(Funded by the U.S. Department of Energy, the U.S. Department of Defense, and the U.S. National Science Foundation)
Researchers from the Molecular Foundry, a user facility at the U.S. Department of Energy’s Lawrence Berkeley National Laboratory, Columbia University, and Universidad Autónoma de Madrid in Spain have developed a new optical computing material from photon-avalanching nanoparticles. This approach offers a path toward realizing smaller, faster components for next-generation computers by taking advantage of intrinsic optical bistability – a property that allows a material to use light to switch between two different states, such as glowing brightly or not at all. For decades, researchers have sought ways to make a computer that uses light instead of electricity. But in previous studies, optical bistability had almost exclusively been observed in bulk materials that were too big for a microchip and challenging to mass produce. Now, the researchers suggest that the new photon-avalanching nanoparticles could overcome these challenges in realizing optical bistability at the nanoscale.

(Funded by the U.S. Department of Energy)
Scientists from the Massachusetts Institute of Technology and the National Institute for Materials Science in Tsukuba, Japan, have discovered that electrons can form crystalline structures in materials composed of either four or five layers of graphene. (Graphene is a one-atom-thick layer of carbon atoms arranged in hexagons, which looks like a honeycomb structure.) Last year, the scientists reported that electrons became fractions of themselves upon applying a current to a material composed of rhombohedral pentalayer graphene and hexagonal boron nitride. This time, the scientists have shown that electrons can become fractions of themselves without a magnetic field. They also found that what they saw last time can be understood to emerge in an electron “liquid” phase, analogous to water, and what they have now observed can be interpreted as an electron “solid” phase that looks like the formation of electronic “ice.”

(Funded by the U.S. Department of Energy and the U.S. National Science Foundation)
Researchers from the University of Connecticut; Harvard University; the Massachusetts Institute of Technology; RTX BBN Technologies in Arlington, VA; and the National Institute for Materials Science in Tsukuba, Japan, have discovered that electrons in twisted trilayer graphene behave unlike those described by Bardeen-Cooper-Schrieffer theory of paired electrons. However, twisted trilayer graphene shares properties with high-temperature cuprates, in which electrons also pair up, but differently from traditional superconductors. Many previous studies in graphene are limited in describing superconductivity, because those experiments focus on the properties of single electrons rather than electron pairs, says Pavel Volkov, one of the researchers involved in this study. “What matters is that electrons form pairs, and somehow you want to probe the properties of those pairs to be able to study superconductivity,” he says.

(Funded by the U.S. Department of Energy and the U.S. National Science Foundation)
Scientists from the University of Oklahoma and Northwestern University have shown that adding a crystalized molecular layer to quantum dots made of perovskite prevents them from darkening or blinking. Quantum dots, which are nanoparticles that have unique optical and electronic properties, usually fade out after 10–20 minutes of use. The crystal coverings developed in this study extend the continuous light emission of quantum dots to more than 12 hours with virtually no blinking. According to Yitong Dong, the scientist who led this study, these findings pave the way for the future design of quantum emitters – devices that emit single photons on demand, with applications in quantum computing.

(Funded by the U.S. Department of Energy)
Researchers from Penn State; Columbia University; the National Renewable Energy Laboratory in Golden, CO; TUD Dresden University of Technology in Germany; King’s College London; Radboud University in the Netherlands; the University of Chemistry and Technology Prague in the Czech Republic; and the University of Regensburg in Germany have identified a surface exciton – an excited electron and the hole it leaves behind – in chromium sulfide bromide, a layered magnetic semiconductor. Cooling chromium sulfide bromide down to around –223 degrees Fahrenheit brings it to a ground state, or the state of lowest energy. This transforms it into an antiferromagnetic system, in which the magnetic moments – referred to as “spin” – of the system’s particles align in a regular, repeating pattern. This antiferromagnetic ordering ensures that each layer alternates its magnetic alignment. As a result, excitons tend to stay in the layer with the same spin. Like cars on alternating one-way streets, these established boundaries keep excitons confined to the layer with which they share the same spin directions.