Dynamics of jammed spin liquid on the kagome bilayer

The Heisenberg antiferromagnet on the kagome bilayer is one of the canonical frustrated spin systems. It also provides a basic model for the compound SCGO that triggered the interest in highly frustrated magnets. The source of the seemingly glassy behavior observed in SCGO at temperatures below $T_g \approx 3.5$ -- 7 K remains unclear even after decades of intensive study. In particular, previous works [1], including our own [2], seem to indicate that dilution alone does not engender a spin glass in its classical spin-liquid ground state. Instead, it is suggested that the glassy behavior likely originates from the interplay between disorder and the coplanarity tendency due to quantum fluctuations~[1,3]. In this work, we study the dynamical properties of an effective Hamiltonian that incorporates the collinear/coplanar tendency through a biquadratic spin interaction. We report unusual relaxation dynamics and the dynamical structure factor of the effective model and discuss their experimental implications.