Spin-Lattice Coupling in the Iron-Pnictide High-Temperature Superconductors

The recent discovery of the iron-pnictide superconductors has generated tremendous excitement, in part because there are many tantalizing similarities to the cuprate superconductors. As with the cuprates, it is strongly suspected that the spins contribute to superconductivity.

There seems to be a strong relationship between the lattice and magnetism in this system. Several authors have discussed the possibility of spin-phonon coupling, but direct experimental evidence has remained elusive.

This work discusses the relationship between the spins and the lattice in the $BaFe_{2}As_{2}$ family. We demonstrate the presence of negative thermal expansion in these materials, which is a strong indicator of spin-lattice interaction.

In addition, we have conducted inelastic neutron scattering experiments to examine the dynamical relationship between the spins and the lattice. In particular, we make use of the phenomenon known as magnetovibrational scattering to search for evidence of spin-phonon coupling. We believe that this is the first work to use magnetovibrational scattering in an antiferromagnetic system as a tool to study the spin-phonon interaction. Our results provide direct experimental evidence for the existence of spin-phonon coupling, with possible implications about the role of phonons in the superconductivity of iron pnictides.