Spin-1/2 kagome-lattice antiferromagnets Cs${}_2$Cu${}_3$SnF${}_{12}$ and Rb${}_2$Cu${}_3$SnF${}_{12}$

Spin-1/2 kagome-lattice Heisenberg antiferromagnet is theoretically known to have a quantum spin liquid ground state, one of the frontiers of condensed matter physics. The search for the model substances has been continued for a long time, and many candidate substances have been reported. Most of them are hydroxide minerals. Here, I review the static and dynamic properties of non-mineral kagome-lattice antiferromagnets Cs${}_2$Cu${}_3$SnF${}_{12}$ and Rb${}_2$Cu${}_3$SnF${}_{12}$.