Condensed Matter Seminars

A spin liquid is a hypothetical quantum ground state of a frustrated Heisenberg magnet conjectured by P.W. Anderson in the 1970s. Its distinguishing features are (1) a lack of magnetic order and (2) a degeneracy that depends on the topology of the system. The status of spin liquids has been recently upgraded from purely speculative to plausible as these ground states were found in relatively simple two-dimensional spin models on square and kagome lattices. Experiments with herbertsmithite yielded clues of spin excitations with fractional spin 1/2 in a kagome antiferromagnet.

I will present a phenomenological Z_2 lattice gauge theory that describes low-energy properties of the spin liquid in a S=1/2 Heisenberg antiferromagnet on kagome. It reproduces many of the characteristic features observed in recent numerical studies of the model, including the ground-state degeneracy, response to quenched disorder, and spinon states near the system's edge.