Elastic signatures of a spin-nematic

Abstract

We study the elastic signatures -- renormalisation of sound velocity and magnetostriction -- of the spin-nematic phase of a spin-$1$ magnet on a triangular lattice described by the bilinear-biquadratic spin Hamiltonian. We show that at low temperatures, the scattering of the acoustic phonons from the Goldstone modes of the nematic phase lead to a powerlaw renormalisation of the fractional change in the sound velocity, $v$, as a function of temperature, $T$, i.e. $\Delta v/v\propto T^3$ as opposed to the same in the high temperature paramagnet where $\Delta v/v\propto T^{-1}$. At the generically discontinuous nematic transition, there is a jump in magnetostriction as well as $\Delta v/v$ along with enhanced $h^4$ dependence on the magnetic field, $h$, near the nematic transition. These signatures can help positively characterise the spin-nematic in general and in particular the realisation of such a phase in the candidate material NiGa$_2$S$_4$.