Amazing stuff! More on the holy grail of room temperature superconductors!
Invest more in superconductivity instead of wasting money on unreliable, environmentally hazardous and heavily government subsidized wind and solar energy!
"When superconductors were discovered in 1911, they astounded researchers with their ability to conduct electricity with no resistance. However, they could only do so at temperatures close to absolute zero. But 1986, scientists discovered that cuprates (a class of copper oxides) were superconductive at a relatively warm -225 degrees Fahrenheit (above liquid nitrogen) - a step toward the ultimate goal of a superconductor that could operate at close to room temperature. ...
Unfortunately, cuprates are a type of ceramic materials, which makes their application at industrial scales difficult - their brittleness, for example, would pose problems. However, if researchers could understand what makes them superconduct at such high temperatures, they could recreate such processes in other materials. ...
“density functional theory” to explore the significance of structural complexity in cuprates by accurately depicting key structural, electronic, and magnetic properties of these materials. In doing so, “we resolve several long-standing puzzles in this material.”
“Can you use this theory to predict many properties of cuprates? The answer is yes,” ... “You have to just do two things. One of them is to use an up-to-date methodology for the calculation. The more important thing is to include the actual complicated structure of the material, because it matters.” ..."
From the abstract:
"Materials-realistic microscopic theoretical descriptions of copper-based superconductors are challenging due to their complex crystal structures combined with strong electron interactions.
Here, we demonstrate how density functional theory can accurately describe key structural, electronic, and magnetic properties of the normal state of the prototypical cuprate Bi2Sr2CaCu2O8+𝑥 (Bi-2212).
We emphasize the importance of accounting for energy-lowering structural distortions, which then allows us to
(a) accurately describe the insulating antiferromagnetic (AFM) ground state of the undoped parent compound (in contrast to the metallic state predicted by previous ab initio studies);
(b) identify numerous low-energy competing spin and charge stripe orders in the hole-overdoped material nearly degenerate in energy with the AFM ordered state, indicating strong spin fluctuations;
(c) predict the lowest-energy hole-doped crystal structure including its long-range structural distortions and oxygen dopant positions that match high-resolution scanning transmission electron microscopy measurements; and
(d) describe electronic bands near the Fermi energy with flat antinodal dispersions and Fermi surfaces that are in agreement with angle-resolved photoemission spectroscopy (ARPES) measurements and provide a clear explanation for the structural origins of the so-called “shadow bands.”
We also show how one must go beyond band theory and include fully dynamic spin fluctuations via a many-body approach when aiming to make quantitative predictions to measure the ARPES spectra in the overdoped material.
Finally, regarding spatial inhomogeneity, we show that the local structure at the CuO2 layer, rather than dopant electrostatic effects, modulates the local charge-transfer gaps, local correlation strengths, and by extension the local superconducting gaps."
"Popular Summary
In the realm of superconductors, copper oxide–based materials known as cuprates have long intrigued scientists due to their unconventional characteristics and high-temperature superconducting potential. However, a microscopic understanding of cuprates has been challenging due to their intricate electronic interactions and lattice distortions. In this work, we explore the significance of structural distortions in accurately depicting key structural, electronic, and magnetic properties in the prototypical cuprate Bi2Sr2CaCu2O8+𝑥 (BSCCO) from first principles. By considering specifically structural symmetry breaking, we resolve several long-standing puzzles in this material.
First, we correctly describe the insulating antiferromagnetic ground state in undoped BSCCO, a crucial achievement since prior theoretical work always predicted incorrect metallic behavior. Accurate undoped-state descriptions are vital for reliable predictions when doping is introduced.
Second, we establish a paradigm for distinguishing structural symmetry breaking from other degrees of freedom, thereby resolving the long debate about the physical origin of the interesting “shadow” Fermi surface.
Furthermore, using a numerical quantum many-body approach, we explicitly study the spin fluctuations in this material. This helps reveal an intimate relationship between local structural distortions and the local correlation strength around copper atoms, which in turn is known to connect directly to superconductivity.
In essence, this research not only explains the dominant cuprate phenomena but also establishes a solid foundation for constructing well-justified effective models with realistic and microscopic insights using first-principles methods. By capturing essential properties of crystal and electronic structures, we offer a valuable resource for future theoretical modeling and potential advancements in these intriguing superconductors."
First-Principles Prediction of Structural Distortions in the Cuprates and Their Impact on the Electronic Structure (open access)
Fig. 1. Crystal and electronic structure of high-symmetry undoped Bi-2212.
No comments:
Post a Comment