This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: Scientists have confirmed the existence of a predicted room temperature superconductor, while explaining the microscopic mechanism that distinguishes it from a similar one discovered several years ago. The work, published in the journal Physical Review B, offers "a theoretical blueprint for the future design of superior superconductor hydrides" the physicists write.
High temperature superconductors have been a holy grail of materials sciences for decades. There has been success in finding metal clathrate superhydrides such as LaH10. ("Superhydrides" are hydrogen-rich materials.) In 2018 the discovery of its superconductivity was announced in a preprint; and half a year later in the journal Nature. Its critical temperature, below which the material is superconducting (offers no resistance to an electric current, and magnetic fields are expelled from the material) was up to -13°C, a record high at the time, albeit at a pressure of 188 billion pascals (GPa)—1.9 million times the atmosphere's surface pressure on Earth.
It is only at such enormous pressures that LaH10 superconducts because only then does it stabilize into the particularly dense, metallic hydrogen-rich crystal phase where lattice vibrations can bind electrons into Cooper pairs. These are coupled electrons that can take on the characteristics of a boson that, unlike fermions, can condense into a ground state because they are not forbidden from doing so by the Pauli exclusion principle. Based on the properties of LaH10, in 2024 other scientists predicted another superconductor among these clathrate metal hydrides, LaSc2H24.
It was found to have slightly better superconducting properties: a critical temperature of 43°C at a pressure of 167 GPa. But it remained to be understood why LaSc2H24 had somewhat better properties, at least as a superconductor, than the earlier LaH10. Now a research group from Jilin University in Changchun, China and Zhejiang University in Hangzhou, China, including some of the same researchers who worked on the prediction, has identified fundamental differences that account for the higher critical temperature.
Despite the theoretical prediction about LaSc2H24, the tools used to make the prediction did not specify why the addition of two atoms of scandium (Sc) would so alter the properties of the simpler LaH10. To study the problem, Yanming Ma, a co-author of both studies who is affiliated with both universities represented in the lists of co-authors, and colleagues realized that the critical temperature of LaH10 is limited by an anisotropy in the material's electronic band structure. The electronic band structure of a solid-state material is the range of energies the electrons may have in the material, as well as the range of energies they may not have.
These metal clathrate superhydrides have unit cells—the smallest repeatable unit—made up of metallic elements surrounded by a "cage" of hydrogen ions. (The structure of LaSc2H24 has fully enclosed lanthanum in a cage of 30 hydrogen atoms and partially enclosed scandium atoms in cages of 24 hydrogen ions.) Hydrogen atoms occupy three inequivalent sites forming these anisotropic layers, creating structurally different properties between the two different layers. The material's anisotropy opens two different superconductivity channels, each having a different value for the critical temperature. Discover the latest in science, tech, and space with over 100,000 subscribers who rely on Phys.org for daily insights. d research that matter—daily or weekly.
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