By Vladimir USTINOV, RAS Corresponding Member, Director of the Institute of Physics of Metals, RAS Ural Branch; Vladimir STARTSEV, Dr. Sc. (Phys. & Math.), Chief Researcher of the same Institute The Institute of Physics of Metals (Ural Branch of the Russian Academy of Sciences), among other research centers, made good headway in refining a wide range of substances... All that became possible owing to the advanced chemical and physical techniques of high- degree purification, of metals too. And so metallic monocrystals were obtained containing but 10 -5 10 -7 percent impurities. When these crystals were cooled from room temperature to that of liquid helium (4.2 K), the free-path length (truck) of conduction electrons in them attained several millimeters. That is to say, the electrons behaved like those in vacuum: without colliding, they could cover distances comparable with the dimensions of a monocrystal. And thus in a sample of ultra-pure tungsten crystals prepared for the purpose electric resistance falls dramatically to a 150,000th fraction of the usual value, while the free path of electrons becomes 6 mm. This means that should such a crystal be placed in an electric field, its electrons will be moving freely from contact to contact. Now, a magnetic field gives rise to electron paths (tracks) in metallic crystals. The form of these paths depends on the Fermi surface(*) geometry of a particular metal, while their dimensions are a function of the magnitude and direction of the magnetic field. But in contrast to free (unbound) electrons in vacuum tubes (in TV-sets, oscillographs and the like) where, because of the electrostatic Coulomb repulsion, their concentration cannot be brought higher than 1010 e/cm 3 , in metals such concentration is up to 1022 e/cm 3 . For this reason we can expect rather strong electronic effects which someday can be used in elements of cryogenic electrotechnical devices. Thus in a monocrystal of ultra-pure tungsten cooled to the l ... Читать далее