Spin waves in quasi-equilibrium spin systems

TL;DR

This paper uses Landau Fermi liquid theory to identify a new regime of spin wave propagation in quasi-equilibrium spin systems, revealing a gapless mode with unique thermodynamic and dynamic properties.

Contribution

It introduces a novel regime for spin wave propagation and derives the dispersion relations, highlighting the existence of a gapless mode in quasi-equilibrium spin systems.

Findings

Discovery of a gapless precessional spin wave mode

Quadratic dispersion of the gapless mode

Significant impact on thermodynamic and dynamic properties

Abstract

Using the Landau Fermi liquid theory we have discovered a new regime for the propagation of spin waves in a quasi-equilibrium spin systems. We have determined the dispersion relation for the transverse spin waves and found that one of the modes is gapless. The gapless mode corresponds to the precessional mode of the magnetization in a paramagnetic system in the absence of an external magnetic field. One of the other modes is gapped which is associated with the precession of the spin current around the internal field. The gapless mode has a quadratic dispersion leading to some interesting thermodynamic properties including a $T^{3/2}$ contribution to the specific heat. We also show that these modes make significant contributions to the dynamic structure function.