Velocity of transverse sound oscillations in the metals

The Bohm–Staver description of sound waves in metals in the jellium model is generalized by taking into account not only the self-consistent electric field but also the second correlation moment of internal electric field that provides shear elasticity. The system of linearized equations that contains the second correlation moment of the field as a new variable is built. The wave equation is worked out and the velocities of longitudinal and transverse sound are found. The estimation of the field correlation value through the sublimation heat and the electronic Fermi-gas energy is offered for the metals. The velocities of transverse sound are found, which matches well the velocity obtained from the shear modules.

Spin-orbit interactions of transverse sound

Spin-orbit interactions (SOIs) endow light with intriguing properties and applications such as photonic spin-Hall effects and spin-dependent vortex generations. However, it is counterintuitive that SOIs can exist for sound, which is a longitudinal wave that carries no intrinsic spin. Here, we theoretically and experimentally demonstrate that airborne sound can possess artificial transversality in an acoustic micropolar metamaterial and thus carry both spin and orbital angular momentum. This enables the realization of acoustic SOIs with rich phenomena beyond those in conventional acoustic systems. We demonstrate that acoustic activity of the metamaterial can induce coupling between the spin and linear crystal momentum k, which leads to negative refraction of the transverse sound. In addition, we show that the scattering of the transverse sound by a dipole particle can generate spin-dependent acoustic vortices via the geometric phase effect. The acoustic SOIs can provide new perspectives and functionalities for sound manipulations beyond the conventional scalar degree of freedom and may open an avenue to the development of spin-orbit acoustics.

Properties of Dislocation Drag from Phonon Wind at Ambient Conditions

It is well known that, under plastic deformation, dislocations are not only created but also move through the crystal, and their mobility is impeded by their interaction with the crystal structure. At high stress and temperature, this “drag” is dominated by phonon wind, i.e., phonons scattering off dislocations. Employing the semi-isotropic approach discussed in detail in a previous paper (J. Phys. Chem. Solids 2019, 124, 24–35), we discuss here the approximate functional dependence of dislocation drag B on dislocation velocity in various regimes between a few percent of transverse sound speed c T and c T (where c T is the effective average transverse sound speed of the polycrystal). In doing so, we find an effective functional form for dislocation drag B ( v ) for different slip systems and dislocation characters at fixed (room) temperature and low pressure.

Магнитозвуковые волны в двумерной электронной ферми-жидкости

The properties of highly viscous fluids at high frequencies become similar to the properties of amorphous solids. In particular, it becomes possible to propagate not only longitudinal sound waves (plasmons for the case of an electron fluid), but also transverse sound waves associated with shear deformations. In this work, transverse sound waves at high frequencies in a twodimensional electron liquid in a magnetic field are studied. The consideration was carried out in the framework of the Landau Fermi-liquid model. It is shown that for a sufficiently large interaction between quasiparticles, the dynamics of excitations of a Fermi liquid is described by the equations of hydrodynamics. The Navier-Stokes equation and expressions for high-frequency shear viscosity coefficients are derived. Based on the equations obtained, the dispersion laws are calculated for transverse and longitudinal magnetosonic waves. It is shown that the cyclotron frequency, which enters in the viscosity coefficients and the dispersion law of transverse magnetosonic waves, is renormalized and typically becomes less than the usual cyclotron frequency, which determines the cyclotron resonance. The latter fact was apparently observed in the photoresistance of highly mobile GaAs quantum wells, in which two-dimensional electrons form a viscous fluid.