Evolution of strong acoustic pulses in metals in transverse magnetic fields
Abstract
Nonlinear evolution of acoustic pulses in metals is considered in a weak transverse magnetic field. It is assumed that the electron flight time across the pulse region is much shorter than the relaxation time τr, while the Larmor radius R of the electron orbit is much larger than the electron mean free path l and considerably exceeds the pulse length L. It is shown that the force exerted by the resonance particles on the lattice has singularities at those points of the pulse which lie at the boundary between the regions of movement of captured and reflected electrons. The peculiarities of the electron force are responsible for a specific evolution of an acoustic pulse in a magnetic field, manifested in the flattening of the potential hump at the peak and the formation of shock waves over the potential well. Similar peculiarities are also observed for a periodic sound wave in which they cause oscillations of the amplitude of the harmonics in a varying magnetic field. The values of the magnetic field for which the harmonic amplitudes have extremal values have been determined. The results of calculations are found to be in good agreement with the experimental data.