Gudimenko V. Peculiarities of nonlinear electrical conductivity of Yanson point contacts based on layered compounds

The thesis is devoted to the study of conductivity in low-dimensional conductive compounds by Yanson point-contact spectroscopy method as well as to the search for physical effects, the use of which can contribute to the creation of new technologies in the field of development of gas-sensitive devices. In the thesis current states of Yanson point contacts of a set of layered compounds under various environmental conditions were studied by Yanson point-contact spectroscopy. As the result, the information about their fundamental parameters was obtained. The conducting and superconducting properties of point heterocontacts Ag(Cu)/SnNb5Se9 were investigated, as a result of the study the value and temperature dependence of the energy gap were determined for the first time. Nanoclusters of the initial substances (NbSe2 and Nb3Sn) were discovered and their relative volumetric concentration (less than 10-7) in the host matrix was estimated. The tunneling spectra of break-junction contacts of the high-temperature superconducting compound YBa2Cu3O7-δ were investigated as well as the Andreev reflection spectra of the point contacts YBa2(Cul-xZnx)3O7-δ (x=0.075). As a result, signs of the presence of s-wave pairing under conditions when d-wave pairing is suppressed were found, and the presence of mixed symmetry of the dx2-y2+-is order parameter near the (110) surface were revealed as well. The conductivity changes of Yanson point contacts based on organic conductor [N-C4H9-iso-Qn](TCNQ)2 under the influence of the human breath were investigated. It was found that multistructural matrices based on such point contacts demonstrate an integral spectroscopic-type response to the action of the human breath.