Identifying topological order in a spin liquid using entanglement entropy

I will talk about some recent works[1,2] which uses an interesting combination of ideas from quantum information and DMRG(density matrix renormalization group) method to study the ground state of kagome antiferromagnet as a quantum spin liquid. There are various proposals for the ground state of this system ranging from magnetic order to valence bond solids and quantum spin liquid(QSL). In another recent paper by Yan, Huse and White[3] it was shown using DMRG technique that the ground state of this system is gapped and shows no sign of valence bond or magnetic order in large system sizes. However the question of identifying a positive signature of spin liquid was left open. The featured papers provides a strong positive evidence of a QSL on the kagome lattice by computing topological entanglement entropy and showing it is consistent with what is expected from a topological spin liquid of Z_2 type.

Ref: 
[1] H C Jiang, Z W and L Balents, arxiv:1205.4289.
[2] S Depenbrock, I P McCulloch and U Schollwock, arxiv:1205.4858.
[3] S Yan, D Huse and S White, Science 332, 1173(2011).