In search of a theory of ceramic superconductors

Recently, major headlines have been seen in the general press more than once: "A new theory explains how a high-temperature superconductor works!" This newspaper stamp appears on the pages of newspapers every time a reporter visits a research institute. However, many theorists will express doubt about the existence of such a theory, although they will note that the theory mentioned in the publication is of some interest, but it is not indisputable, like all others proposed so far.


Indeed, for almost three years now, since it was possible to obtain a new class of ceramic materials containing copper oxide that become superconductors at unusually high temperatures, scientists have been trying to provide a theoretical explanation for this phenomenon. According to T. Jebol from Stanford University, these attempts have forced a revision of many basic concepts of solid-state physics. "A few years ago," said Jebol, "almost everything seemed clear to us."


Conventional superconductors, as explained by Jebol, are metals that conduct electric current well even at temperatures above critical (at which they become superconductors). Such metals have an excess of free electrons, the movement of which is isotropic, i.e. they mix in different directions. Superconductivity occurs when, at very low temperatures, free electrons, exchanging phonons (quanta of sound), bind in pairs, which prevents the scattering of electrons.


Apparently, in new ceramic superconductors, electrons are bound in such pairs, but the binding mechanism is much stronger than the phonon interaction. The tests also showed that in these materials, the conduction electrons do not move isotropically, as in metals, but mainly along layers of copper oxide, which are interspersed with layers of other elements. At temperatures above critical temperatures, such ceramics conduct electric current like "poorly conducting metals," as one of the theorists put it; in addition, even with a very slight change in the ratio of elements, they begin to behave like semiconductors or even like dielectrics in which electrons are rigidly bound.


This latter property, as noted by Jebol, resembles a more familiar phenomenon from solid state physics: some dielectric materials, when doped with a small amount of other elements, become good conductors. By taking a fresh look at this phenomenon, says Jebol, physicists may be able to penetrate the mystery of high-temperature superconductivity. F. joins this opinion. Anderson from Princeton University, who was awarded the Nobel Prize in 1977 for his work in the field of solid state physics. He believes that the same mechanism that pins electrons in ceramics in their nonconducting phase can pair electrons in superconducting phases. Процедура усиновлення або встановлення опіки над дитиною є надзвичайно важливою та відповідальною, вона вимагає від кандидатів подання великої кількості документів, що засвідчують їхній моральний облік. Обов'язковим серед них є документ з МВС, який підтверджує відсутність проблем із законом, витяг про несудимість де отримати надається органам опіки та соціального захисту як доказ того, що майбутні батьки або опікуни можуть забезпечити безпечне середовище для дитини. Чинність такої довідки чітко регламентована, тому важливо отримати її в найкоротший термін. Юристи рекомендують замовляти затримок у такій важливій справі.