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This review is devoted to describing nonequilibrium carrier systems and relaxational and kinetic phenomena in three-dimensional point-contacts. Attention is focused on describing a phonon system which becomes substantially modified under conditions of ballistic transport. In such systems the energy fluxes are limited by the presence of weakly coupled layers of impurity atoms, planar defects, or microscopic-size contacts. The small size of point-contacts, ranging from several to 1000 nm, makes it possible to investigate low-temperature heat and charge transfer on scales less than the characteristic inelastic scattering lengths. A mechanism of phonon transport in the presence of an interface is analyzed, and various models of a planar defect are examined. The special features of interfacial phonon transport, where the transport coefficients are determined not by scattering processes in the volume of a bulk crystal but rather by the properties of the intercrystalline boundary, are studied. The quantum phonon thermal conductivity of point-contacts is studied in detail.

An explanation is proposed for the large deviation from Matthiessen’s rule observed experimentally in the quasi-one-dimensional metal NbSe3, the Fermi surface of which contains several sheets which are isolated from each other. The deviation from Matthiessen’s rule arises as a result of the nonadditive influence on the electron distribution function from processes of electron scattering on lattice defects (Se vacancies) and phonons. It is shown that the experimentally obtained temperature dependence of the electrical conductivity of NbSe3 can be described satisfactorily in the framework of a simplified model of a one-dimensional Fermi surface in the form two pairs of symmetric points in quasimomentum space. Large deviations from Matthiessen’s rule can be explained by the different character of the scattering on lattice defects and on phonons for electrons localized on different structural chains of the quasi-one-dimensional metal.

It has been shown by us in (1) that a t quenching of thin molybdenum wires (d = = 80 pm) in liquid helium-I1 the completeness of fixation of high-temperature thermodynamic equilibrium defects substantially depends on grain size. Full fixation was attained only in the case when samples had a bamboo structure. This points to the fact that the disappearance of defects at supersaturation in a high-temperature region takes place essentially by means of their migration to grain boundaries and to the sample surface. In accordance with the data given in (1) it is believed that the investigated defects were single vacancies. As the nature of high-temperature vacancy sinks of metals with b.c.c. lattices was not studied earlier, we have per-'formed the investigation of this problem with molybdenum of higher frequency and tungsten. IThe samples were thin wires of various diameters: molybdenum wires with 80, 40, 20 p, tungsten ones with 60 pm. By means of high-temperature annealing various grain structures of samples were produced. The purity was estimated by the resistance ratios at 293 and 4.2 K. The 80 p m molybdenum wires had e 29 3/e 4.2 = = 1800 to 2000, the tungsten ones e293/q4.2 =400 to 500.The quenching was produced in liquid helium-I1 (T w 1.5 K). The samples were heated by a current above the liquid helium surface and then they were immersed in helium with simultaneous current shut off. In this case the cooling rate for more massive samples on an initial section (the first 1000°) reached (1 to 2)%10 deg/s and the mean rate cooling nearly to room temperature was (0.6 to 0.8)xlO deg/s.Molybdenum samples of smaller diameters were cooled faster, however by means of capacitors connected with them in parallel the cooling rate was lowered to the above-mentioned values. It enabled us to correlate the completeness of que-ing on samples of various diameters at comparable cooling rates. The employed appa-

The temperature dependence of the electrical resistivity of quasi-one-dimensional NbSe3 is investigated in the interval 78–550 K in the thermodynamic equilibrium and nonequilibrium states. At temperatures of 300–550 K one observes an exponential deviation from the linear dependence on account of the formation of thermodynamic equilibrium Se vacancies. The influence of intrinsic defects (vacancies) on the properties of NbSe3 at 78–300 K is investigated by the quenching method. For samples with excess vacancies an anomalously large deviation from the Matthiessen rule (up to 150%) is observed.