Point-Contact Spectroscopy

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.