Monopole and Dirac string Dynamics in Spin Ice

Magnetic frustration in spin ice gives rise to a highly degenerate Coulomb phase ground state with algebraically decaying spin correlations [1], that acts as a vacuum for local \textit{magnetic monopole} excitations [2]. We shall present how the previously unexplained temperature dependance of the time relaxation for a spin ice material Dy$_{2}$Ti$_{2}$O$_{7}$ [3] can be understood in the light of these emergent quasi-particles connected by a network of classical analogues of \textit{Dirac strings} [4]. These experimental data [3] give a clear signature of fractionalised excitations into pairs of opposite magnetic charges, and the dynamical slow down appears as a consequence of the rarefaction of monopoles at low temperature, strengthened by the influence of the Coulomb interactions on the chemical potential of these quasi-particles. \\[4pt] [1] C. Henley Phys. Rev. B \textbf{71}, 014424 (2005). \\[0pt] [2] C. Castelnovo \& al. Nature \textbf{451}, 42-45 (2008). \\[0pt] [3] J. Snyder \& al. Phys. Rev. B \textbf{69}, 064414 (2004). \\[0pt] [4] L.D.C. Jaubert \& P.C.W. Holdsworth, Nat. Phys. \textbf{5}, 258 (2009).