Two mysteries of high-temperature superconductivity in cuprates have been solved. Room superconductivity in graphite Superconductor at room temperature

23.07.2020

taken from here - http://zoom.cnews.ru/rnd/news/top/sverhprovodimost_pri_komnatnoj_temperature

Superconductivity at room temperaturePhysicists were able for the first time to create superconductivity at room temperature and explain the essence of this phenomenon. Superconductivity lasted less than a second in a ceramic conductor, but this achievement is a huge one in the development of science and technology. Physics Natural sciences

04.12.2014, Thu, 20:51, Moscow time

An international team of physicists led by scientists from the Max Planck Institute in Hamburg was able to use laser pulses to force individual atoms in a crystal lattice to a short time shift and thereby maintain superconductivity. Short infrared laser pulses made it possible for the first time to "trigger" superconductivity in a ceramic conductor at room temperature.

The phenomenon in experiment lasts only a few millionths of a microsecond, but understanding the principle of superconductivity at room temperature can help create new types of superconductors that will revolutionize modern technology. Such superconductors will solve many contemporary problems: will make it possible to create super-powerful batteries for powering energy-intensive equipment like lasers or power drives, electric motors and generators with an efficiency close to 100%, new medical devices, tiny but powerful microwave emitters, etc.

Superconductivity is already being used, for example, in NMR scanners, particle accelerators, high power relays in power plants. However, modern superconductors require cryogenic cooling: metal to -273 degrees Celsius, and more modern ceramic -200 degrees Celsius. It is clear that this greatly limits the widespread use of superconductivity, especially in everyday life.

Unfortunately, it was not possible to create superconductivity at room temperature for many years because of the specific conditions under which it occurs. Thus, one of the most promising ceramic superconductors YBCO (yttrium-barium-copper oxide) has a special structure: thin double layers of copper oxide alternate with thicker intermediate layers that contain barium, copper and oxygen. Superconductivity in YBCO occurs at -180 degrees Celsius in double layers of copper oxide, where electrons can join and form so-called Cooper pairs. These pairs are able to create a "tunnel" between different layers, that is, to pass through the layers, like ghosts through walls. This quantum effect is observed only below a certain temperature.

In 2013, an international team working at the Max Planck Institute discovered that short pulses of an IR laser can induce superconductivity in YBCO at room temperature for a very short time. It was not possible to understand the nature of this phenomenon, only the world's most powerful X-ray laser LCLS (USA) helped to "see" the atomic structure of the material and ultrashort processes. With its help, scientists conducted a series of complex experiments and published the result of their discovery in the publication Nature.

As it turned out, an infrared laser pulse not only makes the atoms vibrate, but also changes their position in the crystal. As a result, the double layers of copper dioxide become slightly thicker - by 2 picometers or 0.01 atom diameters. This in turn increases the quantum coupling between the double layers to such an extent that the crystal becomes superconducting at room temperature within a few picoseconds.

Superconductivity at room temperature: resonant excitation of oxygen atoms causes vibrations (blurred contours) between double layers of copper oxide (layer - blue, copper yellow, oxygen red). The laser pulse brings the atoms out of balance for a short time, the distance between the layers decreases and superconductivity occurs.

Thus, scientists have discovered a potential way to create superconductors that operate at room temperature. If the theory can be turned into a commercial technology (and in the case of current low-temperature superconductors, this took about 20 years), then progress will take a huge leap. Gasoline car engines will become an anachronism, the time of continuous operation of the smartphone will be calculated not in hours, but in months, the heyday of electric aircraft will come, levitating trains and buses on a magnetic cushion.

PS. If this is true and realizable like ceramic lenses are inserted right everywhere now, then .. there is a chance .. oh, if this is true ..

In nature, everything is arranged much more simply than a person assumes in his thinking. For example, everyone is tormented by the question - what is superconductivity? Why does it appear in conductors only when low temperatures Oh ? And the third question is whether room superconductivity? Let's think about this together.

In the manufacture of modern magnets, a mixture of the necessary powders is pressed into the desired shape, then it is inserted into the coil, a current is given, and the magnet is ready. The question is, why is energy stored in the body of a permanent magnet? To answer this question, let's do a second experiment. On the superconducting ring in the cryostat, we wind the wire and connect it to a charged capacitor. When a current is pushed in it, superconducting current and, like in a magnet, a powerful magnetic field is stored and remains for many years. The answer to the last question is extremely simple. In a permanent magnet, when a current is pushed, similar superconducting currents, only in the volumes of atoms and domains, which we visually detect with the help of iron powder on the pole of a magnet, and it should be noted that all this is at room temperatures and above, up to the Curie point. For magnets, this Curie T is the critical temperature for the loss of magnetization, which is similar to that for any superconductor T c - a clear transition temperature to a conventional conductor.

Development scientific knowledge does not have a main road. Sometimes a researcher who has discovered a new fundamental direction in cognition interprets it in the most simplified form due to the few experimental data accumulated by that time. Further, this form, which is not always correct, is picked up by other like-minded people and over time acquires such details and a powerful mathematical apparatus capable of masking its shortcomings that the development of the theory continues automatically. This is what happened with the Drude electronic conductivity, where the energy in the conductor is carried only by electrons. To return in such a state to the original, more correct positions, is already becoming quite difficult; multi-generational training only pushes forward to a dead end, as happened with superconductivity.

Agree that electricity- there is a transfer of energy along the conductor. An electron cannot be an energy carrier in conductors, since it has a constant charge of 1.6.10 -19 Coulomb, which cannot be changed by nature, which is not suitable for energy transfer at all. For some reason, it does not bother anyone that an electron in a conductor moves in the opposite direction from minus to plus, although energy (established by practice) goes from plus to minus (as in an atom, from the nucleus to electrons). Moreover, it has been experimentally confirmed that the speed of an electron even in a metal does not exceed 0.5 mm / s, and the energy in the conductor is transferred at the speed of light. In synchrotron accelerators, a radio frequency electromagnetic wave drags a beam of electrons on itself to accelerate them, and not vice versa. Here the role of the locomotive of the train is in the wave, the electrons are the carriages. In addition, the outer electrons of the atoms of the conductor are connected by chemical bonds, and it is known that when the allowable current moves, the mechanical properties of the conductor do not change, and the most that the electrons are capable of is to jump from atom to atom. An electron can store energy only in the strength (velocity) of its movement, and when braking, dump it in the form of a small chaotic electromagnetic wave of light, which we see in the example of a light bulb spiral. The same thing happens in any conductors, it becomes clear with a short circuit, when the conductor burns out with a bright glow. And the last. Even Hertz, at the dawn of electrical engineering, made an experiment where in an electric line, very clearly, with a simple spark gap, he showed that energy is transferred not only through wires, but mainly between wires, where electrons are forbidden to be. This is where an ordinary electromagnetic wave works. Isn't this all convincing? Only not understanding such simple facts led to a lack of awareness of the phenomenon superconductivity. Where does the electromagnetic wave come from for the transfer of energy in wires and superconductors according to Hertz?

In any conductor, semiconductor, dielectric, there are three strong electromagnetic waves on external valence electrons. There is simply no other such power on external electrons. The first is plasma electronic, in short - plasmaelectronic. Physically, it is an electronic "crowd" due to the Coulomb repulsion of like charges. In magnitude, its energy ranges from one to several electron volts. It is determined from experience by the characteristic energy losses. In practice, volumetric plasma-electronic oscillations are distinguished, and surface oscillations, which are less than volumetric ones by about the root of two.

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The second electromagnetic wave on the outer electrons is the Fermi energy. It is supposedly not determined experimentally anywhere, so the fabrications about it are too diverse. In fact, this is the rotation energy of the outer electron of any atom around the nucleus and nothing more, and the electron receives the Fermi energy from the nucleus, it also has a strictly defined frequency (E f \u003d hH ƒ, where h is Planck's constant, ƒ is the frequency) and is located nearby with plasmoelectronic energy, since the electrons are the same - external atoms. The energy position of plasma electron and fermienergy in any substance in optical spectroscopy is the edge of the main absorption (or the edge of fundamental absorption), where the so-called excitons are found (double-humped energy burst in spectroscopy). For aluminum 1.55 eV, for copper 2.2 eV, for yttrium ceramics 1.95 eV. Energies are always close, but never combined like two identical inductively coupled circuits. If the circuits are irradiated with a frequency, then the frequency of one circuit goes down due to the coupling, and the frequency of the other goes up. And the irradiation of external electrons is one thing - from the nucleus. Note that, for some reason, the fermienergy of metals is slightly lower than the plasma electron one, while the fermienergy of semiconductors and dielectrics is higher than the plasmaelectron one. This is the only reason why metals have a series of sufficiently powerful side frequencies towards zero energy, which makes metals good conductors. And for semiconductors and dielectrics, on the contrary, the low-frequency side ones fall to small sizes (Stokes frequencies), and the high-frequency ones are amplified (anti-Stokes), so they conduct electricity poorly. The change in magnitude of these two energies, which is produced by a push, explains the transition Dielectric - Metal.

The third electromagnetic wave is plasma ion (ion-plasma). It is a generalizing element of all types of thermal vibrations of atoms (phonons). In all substances, it is clearly determined by Raman scattering of light. Let us note that the plasma ion "leads" the whole team various thermal vibrations of the lattice of atoms in substances (phonons), any change in this energy entails a change in their values. In this section, we should especially note the dependence of longitudinal acoustic oscillations (the usual speed of sound in a conductor) on the ion plasma. The energy of the ion-plasma wave does not exceed 0.1 eV, respectively, and its frequency is small compared to electronic waves.

All three electromagnetic waves in conductors, semiconductors, dielectrics naturally add up into a single wave. In quiet matter, it has the form of a standing wave. This single wave in the power line was shown to us by Hertz with a simple spark gap, and now every schoolchild in the physical classroom, and anyone who wants to under a high-voltage power line, can see it with a neon light bulb. In case of any violation of neutrality, even due to an accidental displacement of electrons in the conductor, a single wave rushes to eliminate the violation and, by dragging electrons to their places, restores order like a hostess in an apartment. This movement of electrons when putting things in order is resistance, since they take away energy from a single wave for movement (as in a synchrotron accelerator), and, stopping, dump excess energy in the form of chaotic radiation - heat. There is a weakening of the energy of a single wave by the amount of thermal electron ejection. When there is nothing to take away, she goes into a standing one - the hostess is resting. The separation of inertial electrons also occurs in the Tolman-Stuart experiment, but we measure with a galvanometer only the voltage of a single wave, its excitation. In semiconductors, we, in a purely experimental way, have learned a little to control a single wave. By applying voltage to the ends of the crystal, we change the position of the plasmoelectronic and fermienergy in frequency in the direction of approximation, which causes the value of the resistance to drop. By spreading both energies in frequency (reducing the number of electrons due to the application of plus voltage), we increase the resistance of the transistor. Semiconductors have the closest electronic energies in terms of value, and therefore are easier to regulate.

In nature, there is a resonance of these three electromagnetic waves, two electronic - plasma-electronic and Fermi - with the third ion-plasma. In physics, this fact is known as three-wave resonance. In this case, the difference in the frequency of the electronic energies coincides with the frequency of the ion-plasma. It is known from theory; at the moment of resonance, the total energy of the three waves is alternately pumped into the Fermi, then into the plasma-electronic, then into the ion-plasma waves. When the total energy enters the ion-plasma energy, then the entire spectrum of thermal vibrations of atoms is excited, which is experimentally seen from the heat capacity surge in conductors. At this moment, the speed of sound also increases, which means that the sound wave moves the atoms more densely and stretches along the conductor. When the atoms are compressed between them, the electrons are also compressed, and this is how they receive additional energy from the nuclei, while at the moment of the divergence of the atoms, the excess energy is dumped not randomly, but in the form of pieces into a single electromagnetic wave, but already together, guided by its frequency, according to the laser principle. This addition amplifies the single wave, which is found as negative resistance in semiconductors.

There is another extraordinary factor extremely important for superconductivity. This is how nature arranged that the acoustic wave of compression and rarefaction of atoms among themselves is rather weak in itself, since part of the energy is spent on the formation of heat. But at a certain moment it can be amplified by the thermal vibrations of atoms themselves, and even by several times. This amplification is called Ballistic vibrations (phonons), which occur only at very low temperatures. Amplification occurs only at the moment of transfer of thermal vibrations from chaotic motion to certain directions during cooling, - along strictly defined axes of the crystal due to the weakening of other directions. This factor is the main and determining the beginning of any superconducting transition. Each superconductor, due to the peculiarities of the crystal lattice, has strictly its own ballistic phonons. This was found in high-temperature ceramics in the form of a sharp anisotropy in current conductivity. The temperature inclusion of these vibrations enhances the acoustic wave, it squeezes the electrons to the nuclei of atoms more strongly, which is why the electrons store more energy and significantly reinforce a unified an electromagnetic wave similar to the light in a laser. And from it the resonant ion-plasma energy receives powerful shocks and makes the acoustic wave work more violently. A full-fledged positive feedback is formed, which makes you store in superconducting storage devices of enormous energy incomparable with any conceivable battery. So in superconductors we have two main compatible factors - the emergence of a powerful single electromagnetic wave on external electrons and, due to the occurrence of ballistic oscillations, the creation reinforced reverse energy bonds through an acoustic wave. Electrons, receiving additional energy in this process, accelerate in their orbits, and as two conductors with increased currents of the same direction are attracted to each other against the Coulomb repulsion to the spin "latch" by the magnets. Spin forces are extremely short-range, so they fix the pairing of two electrons only at distances of the order of 10 -12 m. double benefit; the paired electrons do not prevent the single wave from moving and do not take energy from it with their de Broglie waves. And at the same time, constantly pumping up to the nuclei of atoms, they receive energy in shocks, and then pump it together in a single wave to amplify it. Such an electron pair, unlike a pair of chemical bonds, is almost free in space and, due to the poles of its own current magnets, always turns against an external magnetic field, and by its rotation creates diamagnetism of the given substance (a countercurrent occurs in it). The coherence length found experimentally in superconductors, and is the length of the resonant single electromagnetic wave (envelope from the addition of three electromagnetic waves).

It is practically not difficult to verify these considerations. Not a few substances are known with strong diamagnetism even at room temperature, which means that a single wave, somewhat enhanced by resonance, is already working there and there are ready-made electron pairs (for example, СuCl, SiC). It is necessary to take such a substance, determine the acoustic frequency, and instead of ballistic phonons, apply ultrasonic vibrations of sufficient power to it (do the work of ion-plasma energy). This action will strengthen the work feedback and start the energy cycle, the result will be artificial superconductor at room temperature. At the same time, it must be remembered that with insufficient ultrasonic power, only the value of the resistance of the sample will change. It is possible that some crystals with the Gunn effect work on this principle, where powerful electrical vibrations are created. Apparently, there, from the action of the attached electrical voltage above 3 kilovolts, the same ballistic oscillations occur at room temperature, but for some reason short-term, only for the period of oscillation. Ultrasound on small crystals can be replaced by laser pulses with fermisecond times.

According to the above reasoning, it is possible to outline the way of manufacturing room superconductor. It is necessary to take a material with strong chemical bonds for the successful operation of a sound wave, determine all three electromagnetic waves with instruments, and by introducing heavy or light atoms into the crystal lattice, achieve a three-wave resonance. And then adjust the feedback force of the sound wave first with ultrasound (or laser), and then, by experiment, develop a method for excitation of ballistic vibrations. Silicon carbide is suitable for this, and in the future the best superconducting the material will be ordinary carbon, since in its scales the strongest chemical bonds from nature, respectively, for the occurrence superconductivity minimal energy of ballistic vibrations is required.

In conclusion, we note that a superconductor differs from all other materials by an internal, resonant unified electromagnetic wave on external electrons and working in tandem with ballistic vibrations of atoms (phonons). Evidence for this is the experimentally discovered recently volumetric and surface superconductivity BB-link to publication

Thank you so much for your contribution to the development of domestic science and technology!

An international team of physicists led by scientists from the Max Planck Institute in Hamburg was able to use laser pulses to force individual atoms in a crystal lattice to move for a short time and thereby maintain superconductivity. Short infrared laser pulses made it possible for the first time to "trigger" superconductivity in a ceramic conductor at room temperature.

The phenomenon in the experiment lasts only a few millionths of a microsecond, but understanding the principle of superconductivity at room temperature can help create new types of superconductors that will revolutionize modern technology. power drives, electric motors and generators with an efficiency close to 100%, new medical devices, tiny but powerful microwave emitters, etc.

Image copyright Thinkstock Image caption Superconductors can be used to create electrical networks

At about -270 degrees Celsius, some metals pass an electric current without resistance. However, scientists have learned to achieve superconductivity at a higher temperature of about 130 kelvins (-143 Celsius), and do not stop there, believing that this valuable property can be reproduced at room temperature.

Superconductors are characterized by the complete absence of resistance. The so-called superconductors of the first kind completely displace the magnetic field.

Similar substances of the second kind allow the presence of superconductivity and a strong magnetic field at the same time, which makes their range of applications extremely wide.

What is superconductivity?

The phenomenon itself was described by the Dutch chemist and physicist Heike Kammerling-Ottes in 1911. He won the Nobel Prize two years later.

For the first time, the concept of superconductivity appeared in the scientific works of the Soviet academician Lev Landau, who, by the way, was also awarded the Nobel Prize in 1962 for his work.

The superconductivity of metals is explained using the concept of the so-called "Cooper pairs": two electrons combined through a quantum with a total zero angular momentum.

Similar pairings of electrons occur in the crystal lattice of some metals when cooled to extremely low temperatures.

Later, however, using cuprates - ceramics with a high copper content - scientists achieved superconductivity at temperatures significantly higher than the boiling point of nitrogen (-196 Celsius), which, given the widespread production of liquid nitrogen, makes substances with no resistance relatively convenient to use.

Thanks to these experiments, superconductors became widespread and are used today, in particular, for imaging in medical diagnostic devices, such as magnetic scanners and magnetic resonators.

They are also widely used in particle accelerators in physics research.

And then graphene?

Professor of Aalto University of Helsinki and Landau Institute for Theoretical Physics of the Russian Academy of Sciences Grigory Volovik at the Moscow International Conference on Quantum Technologies spoke about the possible obtaining of superconductivity at high temperatures using graphene - flat modification.

Graphene, like superconductors, is predicted to have a bright future - manufacturers of both light bulbs and body armor are interested in it, not to mention its prospects in microelectronics.

Image copyright IBM Image caption Under normal conditions, graphene exhibits the properties of a semiconductor

Its potential was described by theoretical physicists throughout the 20th century, but it came to practical research only in the 21st century: it was for the description of the properties of graphene isolated from graphite that Konstantin Novoselov and Andrey Geim came from Russia.

According to Volovik, knowledge about the properties of electromagnetic fields can make it possible to build a superconductor based on flat energy bands, which can be observed in "ideal" graphene.

And yet - what about room temperature?

The flat zone characteristic of ideal graphene should have zero energy throughout its entire plane.

However, the real structure of the two-dimensional allotropic modification of carbon often resembles a "flattened sausage" in structure, says Prof. Volovik.

Nevertheless, experts do not lose heart: at the moment, theorists are working on several options for the appearance of the necessary for creating superconductivity in room conditions flat energy zone, among which are supercooled gases.

Last year, American physicists from Stanford University figured out how graphene's superconductivity could be put into practice using layers of monatomic carbon - actually, graphene - and calcium superimposed on each other in a "sandwich".

Since just over a year ago, British scientists, we can talk about a noticeable reduction in the cost of production of the necessary materials.

The task, as all the above-mentioned experts say, is now to find ways to produce defect-free graphene in large volumes.

Solid, liquid, gas, plasma... what else?

One of the states of matter for which superconductivity and other quantum effects are observed is the Bose-Einstein condensate, named after the theoretical work of the Indian physicist Satyendra Bose and Albert Einstein.

Image copyright Science Photo Library Image caption Satyendra Bose pioneered the study of particle behavior at zero Kelvin

It is a special form of matter - it is the state of aggregation of photons and other elementary particles related to bosons at temperatures close to zero kelvins.

In 1995 - 70 years after the release of the theoretical justifications of Bose and Einstein - scientists were able to observe the condensate for the first time.

Only in 2010 did physicists manage to obtain such a condensate for photons.

In particular, lecturer of the Skolkovo Institute of Science and Technology Natalya Berloff, who spoke at the conference, described the behavior of polaritons - quasiparticles that arise when photons interact with elementary excitations of the medium.

Berloff said she tried to present the application of quantum theory to Prime Minister Dmitry Medvedev and Deputy Prime Minister Arkady Dvorkovich last summer as a national initiative.

Some of the students of the Skolkovo Institute of Science and Technology are already actively involved in international research - in particular, Berloff's students are part of the team of physicists who describe the behavior of the mentioned polaritons.

Superconductivity is one of the most mysterious, remarkable and promising phenomena. superconducting materials that do not have electrical resistance, can conduct current almost without loss, and this phenomenon is already used for practical purposes in some areas, for example, in the magnets of nuclear tomography installations or particle accelerators. However, existing superconducting materials must be cooled to extremely low temperatures in order to acquire their properties. But experiments conducted by scientists over the course of this and last year have yielded some unexpected results that could change the current state of superconductor technology.

An international team of scientists led by scientists from the Max Planck Institute for the Structure and Dynamics of Matter for the Structure and Dynamics of Matter), working with one of the most promising materials - high-temperature superconductor copper-barium-yttrium oxide (YBa2Cu3O6 + x, YBCO), found that the impact on this ceramic material pulses of infrared laser light causes some atoms of this material to change their position in the crystal lattice for a short time, increasing the manifestation of the superconductivity effect.

Crystals of the YBCO compound have a very unusual structure. Outside of these crystals there is a layer of copper oxide, covering the intermediate layers, which contain barium, yttrium and oxygen. The effect of superconductivity upon irradiation with laser light arises precisely in the upper layers of copper oxide, in which there is an intensive formation of electron pairs, the so-called Cooper pairs. These pairs can move between the layers of the crystal due to the tunneling effect, and this indicates the quantum nature of the observed effects. And under normal conditions, YBCO crystals become superconductors only at temperatures below the critical point of this material.

In experiments conducted in 2013, scientists found that illuminating a YBCO crystal with high-power infrared laser pulses causes the material to briefly become superconductive even at room temperature. Obviously, the laser light has an effect on the adhesion between the layers of the material, although the mechanism of this effect is still not completely clear. And to find out all the details of what is happening, scientists turned to the capabilities of the LCLS laser, the most powerful X-ray laser to date.

“We started hitting the material with pulses of infrared light, which excited some of the atoms, causing them to vibrate at a fairly strong amplitude.”
says Roman Mankowsky, a physicist at the Max Planck Institute,"Then we used an X-ray laser pulse, immediately following an infrared laser pulse, to measure the exact value of the displacements that occurred in the crystal lattice."

The results obtained showed that the pulse of infrared light not only excited and caused the atoms to vibrate, its impact led to a displacement from their position in the crystal lattice. This made the distance between the copper oxide layers and other layers of the crystal smaller for a very short time, which in turn led to an increase in the manifestation of the effect of quantum anchoring between them. As a result, the crystal becomes a superconductor at room temperature, although this state of it can only last a few picoseconds.

“Our results will allow us to make some changes and improve the existing theory of high-temperature superconductors. In addition, our data will provide invaluable assistance to materials scientists who are developing new high-temperature superconducting materials with a high critical temperature. - says Roman Mankovsky, -“And, ultimately, all of this, I hope, will lead to the realization of the dream of a superconducting material that works at room temperature, which does not need to be cooled at all. And the emergence of such a material, in turn, will be able to provide a lot of breakthroughs in a great many other areas that use the phenomenon of superconductivity to their advantage.