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2024: MEPhI took a step towards solving the nature of high-temperature superconductivity
Employees of the Department of Solid State Physics and Nanosystems of the LaPlaza Institute of NRNU MEPhI as part of an international scientific team received direct experimental proof of the phenomenon of mating charge carriers in real space in a family of high-temperature superconducting oxides based on a compound of barium, bismuth and oxygen (BaBiO3) and found out the nature of the abnormal properties of the system. Another step has been taken in the direction of unraveling the nature of high-temperature superconductivity. The results of the study are published in the scientific journal Physical Review Research. This was announced on September 5, 2024 by representatives of the NRNU MEPhI.
Despite the fact that high-temperature superconductivity (HTS) was discovered by Bednors and Müller in an oxide system based on copper back in 1986, there is still no single theory explaining the complex of abnormal properties of superconducting materials. At the same time, tremendous advances have been made in their technological application. On their basis, long superconductors are created, which are used to obtain ultra-strong magnetic fields, create levitation systems for transport, magnetic resonance imaging, current limiters in high-voltage transmission lines, various electric motors, induction energy storage and other similar devices.
As reported, a family of high temperature superconducting oxides based on BaBiO3 was included in the number of high temperature superconductors (HTS) in 1988 after the discovery of such a substance with the inclusion of potassium atoms Ba (K) BiO3 with a transition temperature to a superconducting state of about 30 kelvin. This substance was characterized by a large number of abnormal physical properties, which could be explained if we assume that all charge carriers are in a paired state. However, until now, experiments and calculations have only indirectly indicated the existence of paired charge carriers in the BaBiO3.
Professor of the Department of Solid State Physics and Nanosystems of the Institute of Laser and Plasma Technologies of the NRNU MEPhI Alexey Menushenkov more than 20 years ago proposed the idea of obtaining direct evidence of the existence of local pairing of electrons and holes. To do this, it would be necessary to conduct a complex experiment - with a laser pulse through an optical gap to destroy the paired (two-part) state of the substance by resonant excitation and observe relaxation (equilibrium) in a single-part free electron ensemble system.
Such an experiment required special equipment to excite and monitor the state of the system with femtosecond resolution. This became possible after the construction of the European X-ray free electron laser EuXFEL near Hamburg (Germany) with the participation of Russia.
As the main experimental method, the researchers used x-ray spectroscopy time-resolved tr-XAS absorbances in the soft X-ray region. The destruction of local pairs of electrons and holes was provided by resonant excitation through the optical slit by pulses of an optical laser with a wavelength of 633 nanometers. The X-ray laser pulses allowed XAS spectra to be captured at different delay times of 0.01 to 60 picoseconds after femtosecond-resolution excitation.
 | We observed strong changes in the XAS spectrum, which was interpreted as rapid (<0,3 пикосекунд) разрушение пар носителей заряда и более медленную (0,3 – 0,8 пикосекунд) перестройку решетки из искаженной моноклинной структуры в новое метастабильное состояние с оптимальной кубической решеткой, сохраняющееся как минимум до 60 пикосекунд после возбуждения. told Alexey Menushenkov, head of the experiment |  |
As a result of the experiment, the researchers for the first time obtained direct evidence of the existence of charge carrier pairing in real space in a super-conducting oxide based on barium and bismuth. The transformation of the electron spectrum from the paired (two-particle) state of the system to the single-particle state of the free electron ensemble was also experimentally observed.
| | We identified and explained the mechanism of the transition of the system to an excited metastable single-particle state and established that the pairing of charge carriers determines the nature of the main abnormal properties of the system. It is carrier pairing that is responsible for local lattice distortions, and not vice versa, as, for example, in bipolaronic models. explained the scientist | |
High-temperature superconductors based on bismuth and copper have similar properties and the same structure, therefore, according to the authors of the study, the results of the experiment give impetus to understanding the nature of high-temperature superconductivity.
The work was carried out within the framework of the Federal Scientific and Technical Program for the Development of Synchrotron and Neutron Research and Research Infrastructure for 2019-2027 of the Ministry of Science and Higher Education of the Russian Federation (Agreement No. 075-15- 2021-1352).
2023
Superconductors in future technologies - from levitating trains to fusion reactors
The Moscow Engineering and Physics Institute is conducting research on an amazing quantum phenomenon - superconductivity. As representatives of the project "MAGNIT: Everything about Science and Technology" told TAdviser on September 28, 2023, in the laboratory of superconductivity and magnetic phenomena led by Dmitry Abin, a research engineer at the Institute of Laser and Plasma Technologies MEPhI, the properties of high-temperature superconducting materials and their application in various technologies of the future are being studied.
As the scientist explained, superconductivity is the phase state of a substance characterized by the lack of electrical resistance and the expulsion of magnetic field lines from the volume of the material. According to Dmitry, these properties open up huge prospects in various fields: from medicine and electricity to transport. In particular, the use of superconductors makes it possible to create strong magnetic fields that cannot be obtained in other ways.
If we talk about the use of superconductors in transport, then the concept of magnetic levitation transport is especially interesting. Dmitry Abin and his team are developing levitation systems that can be used in mobile compositions of the future. The system presented in the laboratory, for example, levitates at a height of up to a few millimeters from the surface and is able to withstand significant loads. This could be the basis for creating a new type of transport capable of reaching speeds that exceed the speeds of modern aircraft.
As the scientist said, the basis of their research is the second generation superconducting tape - a unique material that demonstrates zero resistance at the temperature of liquid nitrogen. This tape was learned to be produced on an industrial scale in Russia.
MEPhI scientists are developing various devices from it, including magnets based on the so-called captured magnetic flux. This allows you to create the effect of magnetic levitation - when objects "soar" in the air without touching the support. Dmitry Abin demonstrated the layout of such a levitating system.
The superconducting cylinder, cooled by liquid nitrogen, steadily "hung" over permanent magnets, and at a distance of several millimeters. The pressed superconductor can withstand a load of up to 15 kilograms while maintaining a gap with magnets, the researcher said.
Dmitry Abin also showed a large-scale demonstrator of a magnetolevitation train based on the same principles. Four belt supports cooled by liquid nitrogen supported a platform with a load above the magnetic rails. In fact, this is a working model of a magnetic cushion train capable of speeds over 600 km/h.
The transition of the electric power industry completely to superconductivity is not yet possible. However, such technologies can be used in applications with an existing low-temperature environment. For example, in cryogenic pumps or to store energy in the form of a spun flywheel on a magnetic suspension, the researcher explained.
In addition to transport and power, superconductivity is actively used in medicine to create strong magnetic fields in tomographs. It is also used in scientific accelerators and thermonuclear reactors. So the potential of this amazing quantum effect is far from exhausted, the scientist is convinced.
The MEPhI laboratory is also working on the creation of superconducting bearings and kinetic energy storage devices. Bearings of this type can be used in creo-pumps for pumping liquid gases, kinetic accumulators - for efficient storage of electricity. According to Dmitry Abin, these developments can be widely used in solving technological problems of the future.
Scientists get superconductors of the future by placing atoms one at a time
On September 21, 2023, it became known that scientists from the University of Zurich, together with colleagues from the Max Planck Institute for Microstructural Physics, were able to create various types of superconductors by placing atoms one at a time. The study, published in the journal Nature Physics, points to a promising approach to overcoming the limitations of natural materials and paves the way for fundamentally different states of matter for the electronics and computing technologies of the future.
The electronics of tomorrow depend on the discovery of materials. Sometimes the natural topology of atoms makes it difficult to create new physical effects. To solve this problem, scientists from the University of Zurich developed superconductors by placing atoms one at a time, which led to the creation of fundamentally different states of matter.
Finding answers to questions about how the computers of the future will look and work is an important incentive for basic physical research. There are several possible scenarios - from the further development of classical electronics to neuromorphic and quantum computers.
A common element of these approaches is the use of physical effects, some of which are so far predicted only in theory. Researchers are working hard and using the right equipment to find quantum materials that will realize such effects. But what if suitable natural materials do not exist?
In a recent study published in Nature Physics, Professor Titus Neupert's team at the University of Zurich, in close collaboration with physicists at the Max Planck Institute for Microstructural Physics, presented a possible solution. The researchers created the necessary materials on their own - placing the atoms one at a time.
They focused on new types of superconductors, which are particularly interesting because they show zero electrical resistance at low temperatures. Due to the unusual interaction with magnetic fields, superconductors are often used in quantum computers. Theoretical physicists have spent years researching and predicting various superconducting states.
| | However, so far only a small number of them have been unequivocally demonstrated on materials, Professor Neupert said.
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As a result of the fruitful collaboration, the researchers theoretically predicted how atoms should be ordered to create a superconducting phase, and colleagues from Germany conducted appropriate experiments. Using a scanning tunneling microscope, they moved and placed atoms in the right positions with atomic precision.
The magnetic and superconducting properties of the system were measured by the same method. By placing chromium atoms on the surface of superconducting niobium, the scientists were able to create two types of superconductivity. Previously, similar methods were used to manipulate metal atoms and molecules, but until now it has not been possible to create two-dimensional superconductors in this way.
The results obtained not only confirm the theoretical predictions of physicists, but also give reason to assume what other states of matter can be created in this way and how they can be used in quantum computers of the future[1].
2022: Physicists propose memory element operating at ultra-low temperatures
On February 14, 2022, representatives of MIPT reported that, together with scientists from Stockholm University, they had developed a device capable of controllably changing the phase of the superconducting wave function. Since superconducting electronics deal precisely with the wave function, this device can become one of its basic elements - such as a transistor for semiconductor technology. Scientists controlled the phase switch by moving the Apricosov vortices between specially created "traps" near the Josephson contact. These switches can be used to implement memory operating at very low temperatures. The results of the study are published in the journal Nano Letters. Read more here.
2020: Scientists "Skoltech" and MIPT opened a rule for predicting superconducting metal hydrides
On April 16, 2020, it became known that Skoltech and MIPT researchers and their colleagues discovered a rule that makes it easier to find high-temperature superconductors. Scientists managed to establish a connection between the position of the element in the Periodic Table and its ability to form a high-temperature superconducting hydride. The results of the study, supported by the Russian Science Foundation, are presented in an article in the journal Current Opinion in Solid State & Materials Science.
As reported, superconducting materials have zero resistance and are able to transmit electricity without loss. These properties are of great interest in terms of the practical use of superconductors in electronics and energy networks. Superconducting magnets are already widely used in MRI machines operating in conventional hospitals and in particle accelerators such as the Large Hadron Collider at CERN.
For April 2020, there are two ways to achieve superconductivity, both requiring extreme conditions: either very low temperatures or very high pressures. In the first case, cooling to 100 K (approximately -173 degrees Celsius) or even lower is required. The results of studies show that in metallic hydrogen superconductivity can also manifest itself at temperatures close to room temperature, but for this it is necessary to provide pressure at the limit of technical capabilities - more than 4 million atmospheres.
That is why scientists' views on April 2020 are directed towards hydrides - hydrogen compounds with another chemical element: these compounds can go into a superconducting state at relatively high temperatures and relatively low pressures. The current record holder for transition temperature is lanthanum decahydride, LaH10. In 2019, it was shown that this compound becomes superconducting at a temperature of -23 oC and a pressure of 1.7 million atmospheres. This level of pressure is unlikely to allow practical applications, but nevertheless the results obtained from studies of hydrides-superconductors are important for other classes of superconductors operating at normal pressure and temperature.
Skoltech graduate student Dmitry Semenok, Skoltech Professor and MIPT Artyom Oganov and their colleagues discovered a rule that allows predicting the maximum critical transition temperature to a superconducting state (maxTC) for metal hydride based only on the electronic structure of metal atoms. This finding makes it much easier to find superconducting hydrides.
| | At first, the connection between superconductivity and the Periodic Table seemed to us something mysterious. As of April 2020, we do not fully understand its nature, but we believe that it is due to the fact that the electronic structure of elements at the border between elements s and p or s and d (they are located between the 2nd and 3rd groups of the table) is especially sensitive to crystal lattice distortions, which contributes to a strong electron-phonon interaction, which underlies the superconductivity of hydrides. told Artyom Oganov, Professor of Skoltech and MIPT | |
The scientists not only identified an important qualitative pattern, but also trained the neural network to predict the maxTC value for compounds that lack experimental or theoretical data. For some elements, anomalies were observed in previously published data. The researchers decided to test this data using the USPEX algorithm developed by Professor Oganov and his students for this purpose and allowing the prediction of thermodynamically stable hydrides of these elements.
| | For elements that, according to published data, showed maxTc values too low or too high (according to the conditions of the rule), we conducted a systematic search for stable hydrides and, as a result, not only confirmed the validity of the rule, but also obtained a number of hydrides of elements such as magnesium (Mg), strontium (Sr), barium (Ba), cesium (Cs) and rubidium (Rb). In particular, it was found that in strontium hexahydride SrH6 the value of maxTC is 189 K (-84 oC) at a pressure of 100 GPa, and in the theoretical barium superhydride BaH12 it can reach 214 K (-59 oC). told Alexander Kvashnin, one of the authors of the work, senior researcher at Skoltech and teacher at MIPT | |
In 2019, Artyom Oganov and his colleagues from Russia, the USA and China synthesized cerium superhydride CeH9, which has superconductivity at a temperature of 100-110 K and (relatively) low pressure - 120 GPa. Another superconductor discovered by a research group consisting of Dmitry Semenok, Ivan Troyan, Alexander Kvashnin, Artyom Oganov and their colleagues is thorium hydride ThH10, which has a high critical temperature of 161 K.
| | With a rule and neural network in our arsenal, we can focus our efforts on finding more complex and promising compounds that have room-temperature superconductivity. These are triple superhydrides consisting of two elements and hydrogen. We have already been able to predict several hydrides that may well compete with the LaH10 and even surpass it. told Dmitry Semenok, first author of the work | |
The work was also attended by employees of the All-Russian Research Institute of Automation named after N. L. Dukhov and the Research Computing Center of Moscow State University named after M.V. Lomonosov.
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