Influence of magnetic breakdown on low-frequency conductivity and weak damping electromagnetic waves in metals

Low-frequency electroconductivity under magnetic breakdown conditions is investigated in the two qualitatively different situations: (a) coherent and (b) stochastic. In the former situation (a) the consideration is fulfilled in terms of the incidental magnetic breakdown spectrum of electrons. In the latter situation (b) it is fulfilled in terms of discrete random walking of classical electron. In these cases the general expressions of the conductivity tensor under conditions of both strong and weak spatial dispersion are derived. It is shown that magnetic breakdown does not violate the conditions of compensation of the volumes of electrons and holes in the case of closed trajectories. In the coherent situation the magnetic breakdown has the most essential influence upon Landau adsorption which is determined by a macroscopic layer of valuesP _z (projection of the momentum of the electrons on the direction of the magnetic field). In the stochastic case it is shown that magnetic breakdown results in the appearance of peculiar ergodic states in which an electron is spread on all bands (which take part in the breakdown) with equal probability. Together with it the probability of breakdown disappears from the low-frequency conductivity in a wide interval of magnetic fields and the conductivity is expressed in terms of the classical motion along an united compound orbit. The results of both coherent and stochastic calculations are used to investigate the weak damping electromagnetic waves. It is shown that the magnetic breakdown essentially changes only the dependence of the helicon damping on the magnetic fieldH. In many situations the dependence is represented by nonmonotonic functions ofH. In the coherent and stochastic cases these functions are qualitatively different.