Nature sometimes surprises us with intriguing material behavior. Witness the fractional quantum Hall effect or high-temperature superconductivity. More rarely, theorists conceive of novel systems and then set out to look for them in nature. One such novel system is the spin liquid, 1 postulated in 1973 by Philip Anderson for an antiferromagnetic insulator. In particular, he considered a material featuring planes of spin-carrying atoms arranged in triangular lattices. The atoms are fixed in position but the spins interact antiferromagnetically with their neighbors. Because the triangular lattice frustrates attempts of the spins to order, the spins will not freeze into a fixed configuration, even at the lowest temperature. Thus the system is called a spin liquid.
The spin-liquid concept spurred many theorists to study a variety of magnetic materials in which frustration prevents the development of an ordered state. Lured by the prospect of finding unconventional new phases of matter, experimentalists...
