How many spin liquids are there in Ca₁₀Cr₇O₂₈?

Ca₁₀Cr₇O₂₈ is a novel magnetic insulator with S=1/2 Cr⁵⁺ ions on a bilayer breathing–Kagome lattice. Exchange interactions in Ca₁₀Cr₇O₂₈ are predominantly ferromagnetic, giving rise to a positive Curie-Weiss temperature of 2.35 K. None the less, no magnetic order is observed down to 19 mK, making Ca₁₀Cr₇O₂₈ an unusual example of a two-dimensional quantum spin liquid.
In this talk we explore the nature and origin of the spin liquid observed in Ca₁₀Cr₇O₂₈, using semi-classical molecular-dynamics simulations. We analyze the evolution of spin dynamics in Ca₁₀Cr₇O₂₈ in applied magnetic field, and explicitly compare to published inelastic neutron scattering data.
To our surprise, we find that excitations encode not one, but two distinct types of spin liquids at different time scales. Fast fluctuations reveal a “coulombic spin liquid”, seen by broad “bow-tie” features in the magnetic scattering function which evolve in applied field into distinct “pinch-points”, as known from the classical Kagome antiferromagnet. On the other hand, slow fluctuations reveal a “spiral spin liquid”, which can be seen in form of “rings” in the magnetic scattering function, and understood by a mapping onto an effective spin-3/2 honeycomb model.