Specific features of transport phenomena in gapless semiconductors which are due to both peculiarities of the electron spectrum of an ideal crystal and those of the impurity states in these semiconductors, are discussed. A detailed critical analysis is made of a large number of experimental papers dealing with studies of the conductivity, Hall effect, and magnetoresistance in HgCdTe crystals as a function of temperature, pressure, and magnetic field. On the strength of this analysis it is concluded that the perturbing action of the potential of acceptor-type impurities leads to effective overlap of the valence band with the conduction band. As a result, when the impurity concentration is sufficiently high, and exceeds that at which the Mott-Anderson transition occurs, the density of states of a p-type zero-gap semiconductor differs substantially from that of an ideal crystal, and is similar to that of a semimetal.

The temperature dependences of resistivities ρab in the ab plane and ρc along the c axis have been studied for single-crystal Nd2 − xCexCuO4 + δ ( x = 0.12, 0.15, 0.17, 0.20) films with (001) and (1[equation]...

The temperature and magnetic-field dependence of the components of the conductivity and resistivity tensors are calculated with the quantum corrections due to the weak localization effect and electron-electron interaction taken into account in the diffusion and ballistic regimes. The corrections to the conductivity from the weak localization and electron-electron interaction and also the influence of spin and oscillation effects are taken into account by a renormalization of the transport relaxation time of the electron momentum, with the result that the Drude conductivity becomes temperature dependent. A calculation of the components of the conductivity and resistivity tensors is carried out with the use of the theoretical values of the parameters of the theory of quantum corrections, which are determined solely by the values of the carrier density and mobility of a particular sample. The results of the calculation are compared with experimental results for two-dimensional $n\text{-}\mathrm{In}\mathrm{Ga}\mathrm{As}∕\mathrm{Ga}\mathrm{As}$ structures with double quantum wells. It is shown that taking only the quantum corrections into account with the theoretical values of the parameters does not permit even a qualitative description of experiment, and it is therefore necessary to take additional temperature-dependent contributions to the Drude conductivity into account.