Hexbyte Glen Cove Electrons falling flat: Germanium falls into a 2-D arrangement on zirconium diboride thumbnail

Hexbyte Glen Cove Electrons falling flat: Germanium falls into a 2-D arrangement on zirconium diboride

Hexbyte Glen Cove

Figure 1. Ball-and-stick model for bitriangular Ge lattice on zirconium diboride   Germanium atoms (light and dark blue) spontaneously crystallize into a two-dimensional (2D) “bitriangular” lattice on zirconium diboride thin films grown on germanium single crystals (green: Zr atoms, orange: B atoms). Credit: Japan Advanced Institute of Science and Technology

Scientists have recently revealed, both theoretically and experimentally, that germanium atoms can arrange themselves into a 2-D “bi-triangular” lattice on zirconium diboride thin films grown on germanium single crystals to form a “flat band material” with an embedded “kagome” lattice. The result provides experimental support to a theoretical prediction of flat bands emerging from trivial atomic geometry and indicates the possibility of their existence in many more materials.

The human mind is naturally drawn to objects that possess symmetry; in fact, the notion of beauty is often conflated with symmetry. In nature, nothing epitomizes symmetry more than crystals. Since their discovery, crystals have attracted a great deal of attention not only by their unique “symmetrical” aesthetic appeal but also by their unique properties. One of these properties is the behavior of electrons inside a crystal. From a physical point of view, an electron within a crystal can be fully characterized by its energy and a quantity called “crystal momentum,” which relates to how fast the electron moves in a crystal. The relationship between the energy and crystal momentum of electrons is what scientists refer to as “band ,” which, put simply, is the allowed energy levels for the electrons within the crystal.

Recently, materials scientists have turned their attention towards what are called “flat band materials”—a class of materials possessing a in which the energy does not vary with the crystal momentum and hence resembles a flat line when plotted as a function of crystal momentum—owing to their ability to give rise to exotic states of matter, such as ferromagnetism (iron-like spontaneous magnetism) and superconductivity (zero resistance to electricity flow). Generally, these “flat bands” are observed in special 2-D structures that go by names like “checkerboard ,” “dice lattice,” “kagome lattice,” etc. and are typically observed either within the crystal or at the surface of layered materials. A pertinent question thus presents itself—is it possible to embed such lattices into completely new 2-D structures? Efforts to design 2-D materials have focused on answering this question, and a recent finding suggests that the answer is a “yes.”

Now, in a study published in Physical Review B as a Rapid Communication, an international team of scientists from the Japan Advanced Institute of Science and Technology (JAIST), the University of Tokyo, the Japan Atomic Energy Agency, and Institute for Molecular Science in Japan and Tamkang University in Taiwan, led by Dr. Antoine Fleurence and Prof. Yukiko Yamada-Takamura, has reported a possible new flat band material obtained from germanium (Ge) atoms arranging themselves into a 2-D bi-triangular lattice on zirconium diboride thin films grown on germanium . While the team had already grown this 2-D material years ago, they were only recently able to unveil its structure.

Last year, a part of the team published a theoretical paper in the same journal underlining the conditions under which a 2-D bi-triangular lattice can form a flat band. They found that this is related to a “kagome” (meaning weaved basket pattern in Japanese) lattice—a term originally coined by Japanese physicists in the ’50s to study magnetism. “I was really excited when I found out that the electronic structure of kagome lattice can be embedded into a very different-looking 2-D structure,” recalls Prof. Chi-Cheng Lee, a physicist at Tamkang University, Taiwan, involved in the study, who predicted the presence of flat bands in the “bitriangular” lattice.

The prediction was finally confirmed after the team, in their current study, characterized the prepared 2-D material using various techniques such as scanning tunneling microscopy, positron diffraction, and core-level and angle-resolved photoelectron emission; and backed up the experimental data with theoretical calculations to reveal the underlying bi-triangular lattice.

“The result is really exciting as it shows that flat bands can emerge even from trivial structures and can possibly be realized in many more materials. Our next step is to see what happens at low temperature, and how it is related to the flat bands of the Ge bi-triangular lattice,” says Dr. Fleurence, who is also the first author of this paper.

Indeed, who would’ve thought that a typical, run-of-the-mill semiconductor like germanium could offer such exotic and unprecedented possibilities? The 2-D world might have more surprises up its sleeve than we imagine.

More information:
A. Fleurence et al. Emergence of nearly flat bands through a kagome lattice embedded in an epitaxial two-dimensional Ge layer with a bitriangular structure, Physical Review B (2020). DOI: 10.1103/PhysRevB.102.201102

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Japan Advanced Institute of Science and Technology

Electrons falling flat: Germanium falls into a 2-D arrangement on zirconium diboride (2020, December 4)
retrieved 4 December 2020
from https://phys.org/news/2020-12-electrons-falling-flat-germanium-falls.html

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Hexbyte Glen Cove Biological diversity evokes human happiness thumbnail

Hexbyte Glen Cove Biological diversity evokes human happiness

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Researchers have found that more bird species (pictured: a robin) in the vicinity increase the life contentment of Europeans at least as much as a comparable increase in income. Credit: Senckenberg

Under the current pandemic conditions, activities out in nature are a popular pastime. The beneficial effects of a diverse nature on people’s mental health have already been documented by studies on a smaller scale. Scientists of the Senckenberg Gesellschaft für Naturforschung, the iDiv, and the University of Kiel now examined for the first time whether a diverse nature also increases human well-being on a Europe- wide scale.

To this end, the researchers used the data from the “2012 European quality of Life Survey” to study the connection between the in their surroundings and the in more than 26,000 adults from 26 European countries. Species diversity was measured based on the diversity of avian species, as documented in the European breeding bird atlas.

“Europeans are particularly satisfied with their lives if their immediate surroundings host a ,” explains the study’s lead author, Joel Methorst, a Ph.D. student at the Senckenberg Biodiversity and Climate Research Center, the iDiv, and the Goethe University in Frankfurt, and he continues, “According to our findings, the happiest Europeans are those who can experience numerous different bird species in their , or who live in near- surroundings that are home to many species.”

Birds are well-suited as indicators of biological diversity, since they are among the most visible elements of the animate nature—particularly in urban areas. Moreover, their song can often be heard even if the bird itself is not visible, and most birds are popular and people like to watch them. But there is also a second aspect that affects life satisfaction: the surroundings. A particularly high number of bird species can be found in areas with a high proportion of near-natural and diverse landscapes that hold numerous greenspaces and bodies of water.

“We also examined the socio-economic data of the people that were surveyed, and, much to our surprise, we found that avian diversity is as important for their life satisfaction as is their income,” explains Prof. Dr. Katrin Böhning-Gaese, director of the Senckenberg Biodiversity and Climate Research Center, professor at the Goethe University in Frankfurt am Main, and member of the iDiv. This result becomes particularly obvious when both values increase by ten percent. Fourteen additional bird species in the vicinity raise the level of life satisfaction at least as much as an extra 124 Euros per month in the household account, based on an average income of 1,237 Euro per month in Europe.

According to the study, a diverse nature therefore plays an important role for human well-being across Europe—even beyond its material services. At the same time, the researchers draw attention to impending health-related problems. “The Global Assessment 2019 by the World Biodiversity Council IPBES and studies of avian in agricultural landscapes in Europe clearly show that the biological is currently undergoing a dramatic decline. This poses the risk that human well-being will also suffer from an impoverished nature. Nature conservation therefore not only ensures our material basis of life, but it also constitutes an investment in the well-being of us all,” adds Methorst in conclusion.

More information:
Joel Methorst et al. The importance of species diversity for human well-being in Europe, Ecological Economics (2020). DOI: 10.1016/j.ecolecon.2020.106917

Biological diversity evokes human happiness (2020, December 4)
retrieved 4 December 2020
from https://phys.org/news/2020-12-biological-diversity-evokes-human-happiness.html

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