  Spin liquids are quantum phases of matter that exhibit a variety of novel
features associated with their topological character. These include various
forms of fractionalization - elementary excitations that behave as fractions of
an electron. While there is not yet entirely convincing experimental evidence
that any particular material has a spin liquid ground state, in the past few
years, increasing evidence has accumulated for a number of materials suggesting
that they have characteristics strongly reminiscent of those expected for a
quantum spin liquid.
