Spin dynamics and unconventional Coulomb phase in Nd${}_2$Zr${}_2$O${}_7$

Abstract

We investigate the temperature dependence of the spin dynamics in the pyrochlore magnet Nd${}_2$Zr${}_2$O${}_7$ by neutron scattering experiments. At low temperature, this material undergoes a transition towards an "all in - all out" antiferromagnetic phase and the spin dynamics encompass a dispersion-less mode, characterized by a dynamical spin ice structure factor. Unexpectedly, this mode is found to survive above $T_{\mathrm{N}}\approx 300$ mK. Concomitantly, elastic correlations of the spin ice type develop. These are the signatures of a peculiar correlated paramagnetic phase which can be considered as a new example of Coulomb phase. Our observations near $T_{\mathrm{N}}$ do not reproduce the signatures expected for a Higgs transition, but show reminiscent features of the "all in - all out" order superimposed on a Coulomb phase.

6 pages + 9 pages supp. mat