Helicon Waves in Solids

Abstract

This paper is a comprehensive tutorial-review of theoretical and experimental work pertaining to helicon waves in solids. The discussion of helicon work is divided into two general categories comprising helicon propagation in the “local” and “nonlocal” regimes. We investigate the behavior of a local free-electron metal in a magnetic field to demonstrate the conditions necessary for helicon propagation and to determine the essential characteristics of the helicon wave. These concepts are carried over to a discussion of the behavior of a general anisotropic metal. Solutions to various boundary-value problems are given. For a nonlocal free-electron metal, there are two collisionless mechanisms for the damping of a helicon wave, Doppler-shifted cyclotron resonance, and Landau or transit-time damping. Both of these mechanisms are described and the influence of a finite carrier mean-free-path on these mechanisms is discussed. All of the experimental methods commonly used to study helicon waves are described and compared. A review of both local and nonlocal experimental studies involving the helicon is given. In the local regime, these include measurements of the Hall coefficient and magnetoresistance in metals (including superconductors) while in the nonlocal regime such phenomena as helicon-phonon coupling and Landau damping are described.