# $^{31}$P NMR study of discrete time-crystalline signatures in an ordered crystal of ammonium dihydrogen phosphate. (arXiv:1802.00457v3 [quant-ph] UPDATED)

The rich dynamics and phase structure of driven systems includes the recently
described phenomenon of the "discrete time crystal" (DTC), a robust phase which
spontaneously breaks the discrete time translation symmetry of its driving
Hamiltonian. Experiments in trapped ions and diamond nitrogen vacancy centers
have recently shown evidence for this DTC order. Here, we show nuclear magnetic
resonance (NMR) data of DTC behavior in a third, strikingly different system: a
highly ordered spatial crystal in three dimensions. We devise a DTC echo
experiment to probe the coherence of the driven system. We examine potential
decay mechanisms for the DTC oscillations, and demonstrate the important effect
of the internal Hamiltonian during nonzero duration pulses.