Research of high-temperature superconductor

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Research of high-temperature superconductor

Safiyev E.S.

Kerimova S.M.

Ganieva N.A.

Abstract

Currently, high-temperature superconductivity is one of the most studied areas of physics. This poses very serious and promising tasks for the practical application of superconductivity to scientists and engineers. In the article, high-temperature superconductivity is investigated and studied, and its promising paths are shown. One of these methods is the application of extreme pressures. In addition to hydrogen-containing materials, the article reflects the names of other promising materials.

Keywords: high-temperature superconductivity, super pressure, hydrogen compounds, BCS theory, Cooper pair.

Introduction

Superconductivity is one of the greatest discoveries of the 20 th century. This is a special physical state of certain solids at low temperatures. Experiments show that the electrical resistance of substances mainly depends on their temperature. In 1908, the Dutch scientist G. Kamerling-Onnes took liquid helium for the first time and began to measure the resistance of metals in this liquid, and in 1911 he determined that the electrical resistance of mercury drops to zero at the temperature of liquid helium. Later it became known that in other metals and alloys, the resistance drops to zero, i.e., they become superconducting. Currently, such a situation is found not only in metals and alloys, but also in some semiconductors and ceramic materials, and also due to the influence of not only temperature, but also high pressure, and their number continues to increase. On fig.1 shows elements that can become superconductors.

Fig. 1. Periodic table of superconductors

high temperature superconductor

An important physical phenomenon in superconducting substances is the repulsion of the magnetic flux from their bulk. If superconductivity were limited only by the loss of electrical resistance, then it would have to be explained by the laws of classical physics. According to the classical theory, the resistance of metals should gradually decrease with decreasing temperature. Already at that time, according to some scientists, the movement of electrons should stop at very low temperatures and the metal should not conduct current. An important physical phenomenon in superconducting substances is the repulsion of the magnetic flux from their bulk. If superconductivity were limited only by the loss of electrical resistance, then it would have to be explained by the laws of classical physics. According to the classical theory, the resistance of metals should gradually decrease with decreasing temperature. Already at that time, according to some scientists, the movement of electrons should stop at very low temperatures and the metal should not conduct current [1,3].

For the first time, the explanation of superconductivity at the microscopic level was given in 1957 by the scientific work of American physicists J. Bardeen, L. Cooper and J. Schrieffer. The central element of their theory, called the BCS, is the Cooper pair of electrons. Once again, it was established that superconductivity is really con - nected with the attraction between electrons in metals and that it has a quantum nature. Later it was discovered that superconductivity has two groups: type I and type II superconductors. Superconductors of the first kind lose their superconductivity in the entire volume when the magnetic flux enters the material with a jump at the value H=Hi. In type II superconductors, the transition of the magnetic field into the material occurs gradually in the interval between the lower critical field value Нц and the upper critical field value Hit2 , and superconductivity completely disappears. When a current flows through a superconductor, a certain magnetic field is created around it. At the maximum critical current density Ji, this field destroys the superconducting state. Superconductivity has been found in more than 25 simple substances (mainly metals), a large number of alloys, intermetallic compounds, and complex oxides of transition metals. Note that among pure metals, the highest critical temperature (9.25 K) was observed for niobium (Nb). In the 1950, it was critical to find superconductors that could withstand strong magnetic fields and emit high current densities for use in powerful electromagnets. In 1954, superconductivity was discovered in the Nb3Sn compound. A wire made of this material was capable of generating a current with a density of 100 kA/sm2 in a magnetic field of 8.8 Tl at a temperature of 4.2 K. In 1962, the English physicist B. Josephson (England) gave a theoretical explanation for the presence of stationary and nonstationary effects in a superconductor-insulator- superconductor contact based on the BCS theory [2]. In 1963, the stationary effect was confirmed experimentally by the American physicists F. Anderson and J. Rowell. In 1973, J. Gavaler (Westinghouse) discovered that thin GeNb3 films made from an alloy of niobium with germanium become superconductors at 23.2 K. However, other intermetallic structures based on niobium require a lower temperature to become superconductive. In the same year, D. Johnston (University of California , San Diego, USA) showed that lithium titanate, lithium oxide, and titanium oxide are su - perconductors at 13.7 K. Two years later, A. Slate (company DuPont) reports that oxides of barium, bismuth and sulfur exhibit superconductivity at somewhat higher temperatures. In 1981, C. Michel and his colleagues (University of Caen-Normandie, France) showed that the perovskite crystalline compound of lanthanum, barium, copper and oxygen synthesized by them has metal-like conductivity at temperatures from plus 300)OC to minus 100OC. However, they did not study this compound at lower temperatures. In 1985, those engaged in the search for metal oxides, including superconductors for perovskites, at I. Bednorts and K. Muller (the Zurich Research Center of the IBM Corporation) got acquainted with the articles of the Cannes-Normandy Univer- sity.They synthesize barium and lanthanum variants of the product substance in different concentrations. The goal was to "capture" additional electrons from copper ions in order to increase the density of mobile charge carriers. Scientists believed that the resulting crystals would have non-standard electrical properties at very low temperatures, possibly superconductivity. In January 1986, I. Bednorz and K. Muller obtained a superconductor with a critical temperature of 35K. They kept this discovery secret for three months and repeated experiments, and for some reason refrained from publishing their sensational results. In September of the same year, their five-page paper was published in the Zeitschrift fur Physik without prior peer review. A year later, the authors were awarded the Nobel Prize. In November 1986, Professor P. Chu (University of Houston) and his colleagues read the article. They repeat the experiment after a short time, compressing the joint with high pressure, raising the critical temperature by 10 degrees. In the same autumn, K. Kitazawa (University of Tokyo) proved that the Zurich superconductor consists of layers of copper ions, each of which is located in the center of an octahedron with six strongly defor.

Between these layers are lanthanum and barium atoms, which form an ordered lattice. This crystal structure with the chemical formula Lal, 8BaO, 2CuO4 is one of the layered exotic perovskites. P. Chu and K. Kitazawa presented their results at the annual conference of the Society for Research in Materials in Boston on December 4th. These reports initiated the search for high-temperature superconductors. P. Chu suggested that the critical temperature increases due to a decrease in the distance bet - ween oxygen octahedra during compression. After returning from Boston, he tests this idea. To do this, by replacing barium with strontium chemically close to it, a structurally close compound is obtained. The hypothesis is justified: the new sub stance becomes a superconductor at 39K (this result, independently, was also obtained in Zurich). Physicists from Houston and colleagues from the University of Alabama synthesized a compound of yttrium, barium, copper and oxygen with a critical tem - perature of 93K in January 1987 using yttrium, an analog of lanthanum. Thus, for the first time, a substance was obtained that loses electrical resistance at a temperature above the boiling point of liquid nitrogen (77K). The structure of the new super conductor was soon determined in several laboratories and presented at a conference of the American Physical Society in New York in March 1987. After that, a new era of high-temperature superconductors began. In 1988, the group of P. Grant (IBM Research Center, Almaden) reported on the superconductor CaBaCuO with a critical temperature of 125 K. Five years later, it turned out that the synthetic compound HgBa2Ca2Cu3Ox (where x is slightly more than 8), obtained by the group of Yu. Antipov (Moscow State University), becomes superconductive at 135 K, and at 160 K with careful compression. This substance is the compound with the record maximum critical temperature at normal temperatures over the last century.

In the 21st century, the list of high-temperature superconductors has qualitatively expanded. In 2001, Japanese physicists surprised their colleagues by discovering superconductivity at 39 K in magnesium diboride (MgB2), a known simple intermetallic compound. Five years later, more interesting information came from that country. X. Hosono and his colleagues (Tokyo University of Technology) discovered for the first time superconductivity in a substance containing iron (Fe) at normal temperature. The critical temperature of the LaOFeP compound was only 5K, but the discovery was not convincing, because pure iron could become a superconductor only at high pressure at temperatures close to absolute zero.Then several more superconductors containing iron and antimony (Sb) were discovered. In recent years, the number of iron-containing superconductors has expanded with unexpected compositions, some of which contain no oxygen at all. In special cases, the critical temperature of iron and selenium doped with potassium, cesium or thallium may exceed 30K. The history of the discovery of superconducting materials until 2015 is shown in Figure 2.

Fig. 2. History of the discovery of superconducting materials

As the temperature of the superconductor rises, the chaotic vibrations of its particles increase, the "activity" of the Cooper pair and even the pair itself is destroyed. Researchers have spent decades searching for a superconductor that forms dense bond pairs at ordinary temperatures. Back in 1968, Professor of Solid State Physics N. Ashcroft (Cornell University, USA) suggested using crystals of hydrogen atoms for this [5,6]. The small size of these atoms allows the electrons to approach the lattice sites and enhance their interaction with their oscillators. it takes very high pressure to turn hydrogen into a metal. However, the work of N. Ashcroft gave hope for providing superconductivity in metallic hydrogen at technical pressures that can be combined with any second element. Rapid development in this direction began in the early years of the 21st century. Using the possibilities of supercomputer modeling, scientists were able to predict the properties of various hydrides. Using compact diamond dungeons, the researchers were able to test the extreme properties of the most promising substances. Hydrides emerged as a new class of superconductors. In 2015, German scientists proved that the metallic form of hydrogen sulfide turns into a superconductor at a temperature of -70°C and a pressure of 152 gigapascals (1.5 million at mospheres). Four years later, he discovered the superconducting state of lanthanum hydride in the laboratory at -24°C and a pressure of 182 gigapascals (1.8 million at mospheres). Another group of scientists in 2018 proved that this compound is super conducting at an anomalously high temperature of -13.3°C. The periodic table of binary hydride semiconductors is shown in Figure 3.

It is known that methane and hydrogen sulfide form a stable combination with hydrogen at high pressures. Here, a hydride acts as a matrix, and hydrogen molecules are located inside it. According to the Migdal-Eliashberg theory, such materials are candidates for superconductors that create Cooper pairs with strong electron -photon coupling at high pressures. When compressed, methane itself decays into 5 million atmospheres without becoming a superconductor, but this problem can be solved in the CH4-H2S-H2 ternary system.

Fig.3. Periodic table of binary hydride semiconductors.

As a result, they managed to obtain a stable compound with a higher critical temperature than binary hydrogen sulfide. In 2019, under the guidance of the American physicist R. Diaz, a high-temperature superconducting substance was synthesized for the first time, capable of retaining its properties up to room temperature [8]. This substance is a crystal based on the hydrogen sulfide, methane and hydrogen shown above. This crystal is grown using a laser beam. At temperature, the resistance of the sample decreases to zero, that is, it becomes superconducting. In an experiment carried out in diamond anvils, it was possible to increase the transition temperature by increasing the pressure (Fig. 4).

The best result was 287.7 K (about 15°C) at 2.67 million atmospheres. At this pressure, the electron layers of atoms are compressed towards each other in such a way that they meet and create a state of collective conductivity, even if at ordinary pressure they are a dielectric substance. The state of superconductivity is preserved in this substance in a wide range of pressures, 1.4-2.8 million atmospheres. With an increase in the influence of an external magnetic field, the critical slope temperature decreases and drops to -5°C at 9 Tesla. According to theoretical modeling, the super conductivity of this material should be maintained up to 62 Tesla. В 2020 French scientists P. Lubeyr (French Atomic Energy Commission) confirm Diaz's experiment on the production of metallic hydrogen at pressures above 400 gigapascals.

Fig. 4. Diamond dungeon and core for studying superconductivity

Other directions in the search for super conductivity, including high-temperature superconductivity, are also being considered. Professor G. Volovik from Aalto University in Helsinki (Finland) spoke at the Moscow International Conference on Quantum Technologies about the possibility of obtaining high-temperature extreme heat in graphene, which is a planar modification of carbon obtained from graphite and has unique properties. Currently, theoretical scientists say that the formation of high-temperature superconductivity occurs in supercooled gases. One of the states of matter in which superconductivity and other quantum effects can manifest itself is the Bose-Einstein condensate. This is a special form of matter, which is an aggregate state of photons and various elementary particles belonging to bosons at temperatures close to zero Kelvin.

CONCLUSION

When studying high-temperature superconductivity, the article found that the state of three-component compounds at high pressures should be studied by mathematical modeling of their phase diagrams. However, modeling also fails to explain the transition to superconductivity at such high temperatures.

As a result of the research, it was found that scientists were not able to study all the properties of the substance they prepared. Since hydrogen atoms are very small and the crystal structure of a substance cannot be determined by traditional methods, researchers cannot explain the arrangement of atoms in the resulting substance and its chemical formula. But the importance of the studies is that they indicate the direction of the search for high-temperature superconductivity.

REFERENCES:

1. Ssfiyev E.S., Ksrimova S.M. Yukssk temperaturlu ifratkegiriciliya dogru Ener- getikanin problenlsri № 1 2022 s 46-53

2. В.Н. Кушнир сверхпроводимость слоистых структур монография Минск БНТУ 2010. Стр 233.

3. Гинзбург В.Л., Андрюшин Е.А. Сверхпроводимость. Изд. Альфа-М, 2010110с.

4. Шамрай В.Ф. Bi-ВТСП: Структура и сверхпроводимость. Изд. МИФИ, 2011-64с.

5. W.Buckel, R.Kleiner. Superconductivity:An Introduction. Wiley, 2015 - 496p.

6. https://atomicexpert.com/ superconductivity_at_room_temperature

7. https://ria.ru/20210311/ sverkhprovodnik-1600776584 .html

8. https://rscf.ru/news/release/sozdano-nevozmozhnoe-sverkhprovodyashchee

9. https://22century.ru/chemistry-physics-matter/92261

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