Science 350, 655–658 (2015)

Credit: AAAS

Frustrated antiferromagnetic interactions occur in materials where, due to the lattice geometry, the atomic spins cannot simultaneously minimize the energies of their local interactions. For instance, if the spins are arranged in an equilateral triangle, two of them can be antiferromagnetically coupled, yet the third cannot be similarly coupled to the other two simultaneously. This situation is found in antiferromagnetic materials with kagome lattices. The exact nature of the ground state of these materials — or minimum energy state, achievable by cooling them down — has been under debate. Now, Mingxuan Fu and colleagues report experimental evidence based on nuclear magnetic resonance and magnetic susceptibility characterization, showing that the ground state of the kagome antiferromagnet ZnCu3(OH)6Cl2 is a disordered state — namley, a spin-1/2 spin liquid — with a finite gap between this and the excited states. These results clarify the fundamental issue of the ground state of these frustrated antiferromagnets and open up the possibility of experimentally studying this quantum state.