μSR study of the quantum dynamics in the frustrated S=3/2 kagome bilayers

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We present μSR experiments in the S=3/2 kagome bilayer compound Ba₂Sn₂ZnGa₁₀₋₇ₚCr₇ₚO₂₂ (BSZCGO(p)) and compare it to the isostructural SrCr₉ₚGa₁₂₋₉ₚO₁₉ (SCGO(p)), including for the latter new results for p≥0.89. Quantum-dynamical low energy magnetic excitations are evidenced in this novel compound. We study the evolution of the muon relaxation rate with p, T and field. A phenomenological model for the muon relaxation based on sporadic dynamics due to spin excitations in a singlet sea proposed by Uemura et al. [Phys. Rev. Lett. 73, 3306 (1994)]. is extended to all fields and T-range. Its connexion to the RVB picture is discussed, and we argue that such coherent states might mediate the interactions between "impurities" which induce the spin glass freezing.