I.K. Yanson – författare

The physical principles of spectroscopy of quasi-particle excitations in metals at low temperatures by means of point contacts are presented. The point contact constitutes a tiny metallic bridge connecting bulk electrodes. Along with the most thoroughly studied phono excitations, the interaction of electrons with other quasiparticles (magnons, crystal-field electron excitations, paramagnetic impurities, two-level systems, etc), are reviewed. Various experimental techniques for point contact production are described. Examples of point-contact spectra are presented for pure metals, alloys and compounds, as well as for semimetals and semiconductors, heavy fermion systems, Kond-lattices, mixed valence compounds and more. Superconducting point contacts are considered in respect to Andreev reflection and Josephson effects. Special attention is paid to contact conductance fluctuation, and new trends of research are outlined.

The main goal of solid-state physics is investigation of the properties of the matter including the mechanical, electrical, optical, magnetic, and so on with the aim of developing new materials with defined characteristics. Nowadays, the synthesis of superconductors with high critical temperature it consists of or fabrication of new heterostructures on the base of semiconductors, in cre­ ation of layered, amorphous, organic, or nanofabricated structures and many others. To do all of these, the various methods of investigation are developed during the past. Because it is impossible to find an universal method to in­ vestigate a variety of materials, which are either conducting or insulating, crystalline or amorphous, thin-layered or bulk, magnetic or segnetoelectric, and so on, various kind of spectroscopies, like optical, neutron, electron, tun­ nel and so on, are widely used in solid-state physics. Recently, a new type of spectroscopy, namely, the Point-Contact Spectroscopy (PCS), wasdesigned for study of the conduction-electron interaction mechanism with a whole class of elementary excitations in the solids. In PCS, a small constriction, about a few nanometers large, between two conductors plays a role of a spectrome­ ter. Namely, because of inelastic scattering of accelerated electrons, the I - V characteristic of such a tiny metallic contact is nonlinear versus an applied voltage and its second derivative surprisingly turns out to be proportional to the electron-quasiparticle-interaction spectrum.