Phonon spectrum of the ferromagnetic superconductor UGe$_2$ : Consequences for the specific heat

TL;DR

This study investigates the phonon spectrum of UGe₂, a ferromagnetic superconductor, finding no phonon spectrum changes with temperature and clarifying the origin of excess specific heat as magnetic, not phononic.

Contribution

The paper provides inelastic neutron scattering data showing phonon spectrum stability and attributes the excess specific heat to magnetic effects, not phonons.

Findings

Phonon spectrum remains unchanged upon cooling.

Excess specific heat is explained by magnetic order, not phonons.

Phonon contribution to specific heat is quantitatively estimated.

Abstract

We report inelastic neutron scattering measurements of the phonon spectrum of the pressure-induced ferromagnetic superconductor UGe$_{2}$. No changes of the spectrum were found on cooling down to low temperature. The phonon contribution to the specific heat was estimated from a fit to our data. The excess specific heat previously noted at around $T_{x} \approx$ 30 K is not due to phonons but is well described by the temperature dependence of the magnetic order parameter at the molecular field level.