Without exaggeration, the unique experiment carried out at the European X-ray free electron laser EuXFEL (Germany) by an international team of scientists led by MEPhI professor Alexei Menushenkov can be considered a real breakthrough. Their results, published in the prestigious journal Physical Review Research, may put an end to the explanation of the phenomenon of high-temperature superconductivity.
Let us remember that the phenomenon of superconductivity itself, first observed at the beginning of the 20th century at a temperature close to absolute zero (-273.15 C, 0 degrees Kelvin), became one of the most remarkable discoveries in physics. Since then, this phenomenon has always attracted scientists, because its implementation allows to radically solve the problem of gigantic energy losses during its transmission.
The worldwide sensation of 1986 was therefore the report that the superconductivity effect was achieved at high temperatures, around 35 K, in copper-based oxide systems (cuprates). The importance of this discovery is underlined by the fact that its authors, Georg Bednorz and Karl Müller, had already been awarded the Nobel Prize in 1987.
Since then, tremendous progress has been made in the practical application of high-temperature superconducting cuprates, which are used in various fields of science and technology, particularly in medicine, transportation, motors, energy storage devices, etc.
At the same time, a strange situation has arisen with high-temperature superconductivity. It is confidently conquering new frontiers, but science does not have a single explanation for the phenomenon itself. Although traditional low-temperature superconductivity was described many years ago in the Bardeen-Cooper-Schriefer theory. It holds that at very low temperatures, in the so-called momentum space, electrons form bound pairs. Such tandems do not dissipate defects and impurities, which guarantees zero resistance to current.
This theory works for low-temperature superconductivity, but it does not explain the phenomenon of high-temperature superconductivity, although almost immediately after its discovery, scientists proposed dozens of hypotheses. As is usual in science, the truth is reached in different ways. In this case, scientists observed that in the high-temperature “family”, along with cuprates (based on copper), there are others based on barium and bismuth (BaBiO 3). In addition, they have a whole series of anomalous properties.
More than 20 years ago, MEPhI professor Alexey Menushenkov, conducting a series of experiments using synchrotron radiation, put forward an unexpected hypothesis: in BaBiO 3, not only electrons, but also “holes” are bound in pairs. (The hole that forms after the electron leaves the atom has a positive charge.) This is how the idea of the experiment was born. “If an electron-hole pair exists, then when it is resonantly destroyed by a powerful laser pulse, the X-ray absorption spectra of the released charge carriers should radically change,” the scientist explained to RG.
To carry out such an experiment, unique equipment was required. This became possible after the European free-electron X-ray laser EuXFEL was built with the active participation of Russia. Working at this unique facility, Alexei Menushenkov’s team was the first in the world to obtain direct evidence of the existence of charge carrier pairs in real space.
It is important to note here that these experiments were carried out only on the BaBiO 3 “family” and did not include cuprates. However, since both have the same structure and properties, according to the authors, the results of a single experiment bring science seriously closer to understanding the nature of high-temperature superconductivity.
