SCIENTIFIC EDUCATIONAL CENTER science idea

Employees of the Chemical and Physical faculties of Moscow State University, together with colleagues from the Lebedev Physical Institute of the Russian Academy of Sciences, studied an intermetallic compound of gallium and molybdenum with unusual superconducting properties. Scientists have managed to prove that surface and bulk superconductivity are separated in this substance. The work was carried out within the framework of the national project "Science and Universities", which is designed to support and develop scientific activities and education in Russia, and funded by the Ministry of Science and Higher Education of the Russian Federation, project No. 075-15-2021-1353. The result is published in the journal Intermetallics.

Superconductors attract a lot of attention due to their unique ability to transmit electricity without loss. One of the fundamental parameters of a superconductor is a superconducting gap. This is an energy quantity associated with the features of the superconducting state.

Most of the superconductors can be described using the theory of BCS, named after the first letters of the surnames of its creators: Bardin, Cooper and Schrieffer. This theory well describes superconductors with a single slit and a small change in heat capacity during a phase transition, as well as with a weak electron-phonon interaction. These include metals and intermetallic compounds, which were very actively studied in the forties, fifties and sixties of the last century.

"Now we are trying to find out why there are superconductors that are not described by the theory of BCS," said the head of the study, Head of the Department of Inorganic Chemistry at the Faculty of Chemistry of Moscow State University, Corresponding Member of the Russian Academy of Sciences Andrey Shevelkov. – For example, double-slit superconductors. Very few are known, only three proven and a dozen suspected. Therefore, we do not know what properties they have, how the presence of two slits affects them. The only way to understand is to find them and investigate them thoroughly."

For several years, there has been debate in the literature whether the intermetallic compound of gallium and molybdenum, Mo8Ga41, can be a double-slit superconductor. The data were contradictory, and due to the very strong electron-phonon interaction, this superconductor does not fall within the framework of the BCS theory, so it is difficult to describe its parameters and understand its behavior.

"In our work, we managed to show that this is a very specific single–slit superconductor," explained Andrey Shevelkov. – It combines different physical properties: bulk and surface superconductivity. Therefore, in physical measurements, it seems that there are two slits in this superconductor. In fact, one refers to the volume of a substance, and the other refers to its surface."

Four main research methods were used to clarify this issue. For example, a very accurate X-ray diffraction analysis using synchrotron radiation, with which you can evaluate the quality of the lines and understand their features. Measurements of magnetic and superconducting properties and data from two types of spectroscopy were also used: nuclear magnetic resonance and nuclear quadrupole resonance. The combination of these methods and the analysis of the data obtained made it possible to give a definitive answer to the question posed.

"It is not yet known what use compounds of this type may find in the future," explained Andrey Shevelkov. – However, when superconductivity is combined on the surface and in the volume, interesting properties may arise. For example, it is theoretically possible to create a superconductor that will be partially pushed out by a magnetic field, that is, combine magnetism with superconductivity in one substance."

Information and photos provided by the press service of the Moscow State University

Photo author: Ksenia Liokumovich, Yulia Chernova / press service of the Faculty of Chemistry of Moscow State University

The information is taken from the portal "Scientific Russia" (https://scientificrussia.ru /)