Valence Bonds in Random Quantum Magnets: Theory and Application to YbMgGaO4

Understand

We analyze the effect of quenched disorder on spin-1/2 quantum magnets in which magnetic frustration promotes the formation of local singlets.

• Our results include a theory for 2d valence-bond solids subject to weak bond randomness, as well as extensions to stronger disorder regimes where we make connections with quantum spin liquids.
• We find, on various lattices, that the destruction of a valence-bond solid phase by weak quenched disorder leads inevitably to the nucleation of topological defects carrying spin-1/2 moments.
• This renormalizes the lattice into a strongly random spin network with interesting low-energy excitations.