Nuclear Magnetic Resonance in Random Fields: Cluster Formation and Local Dynamics of a Deuteron Glass

NMR data show that the deuteron "pseudo spin-glass" transition in ${\mathrm{Rb}}_{1-x}{\left(\mathrm{N}{\mathrm{D}}_4\right)}_x{\mathrm{D}}_2\mathrm{P}{\mathrm{O}}_4$ is not just a simple kinetic slowing down process but is characterized by a gradual condensation of randomly polarized clusters as expected if we deal with a percolation transition in eigenstate space. The results provide novel information on the temperature dependence and distribution of local random fields and their dynamics. The spin-lattice and motional-narrowing data further suggest that the "pseudospin" O—D--O deuteron intrabond motion determines the freezing dynamics.