Elementary excitations in a diluted antiferromagnetic Kagomé lattice

Thermodynamic studies as a function of dilution in the Heisenberg antiferromagnetic Kagom\'e spin glass ${\mathrm{SrCr}}_{9\mathit{p}}$${\mathrm{Ga}}_{12\mathrm{\ensuremath{-}}9\mathit{p}}$${\mathrm{O}}_{19}$ are presented. The unusual ${\mathit{T}}^{2}$ specific heat is found to be robust towards dilution, implying an origin intrinsic to the spin-glass state. The extremely small excitation stiffness and known correlation length indicate an unusual form of elementary excitation, with similarities to a hydrodynamic mode in a liquid.