Exact Diagonalization studies of Entanglement Entropy of zig-zag spin chains with Heisenberg and ring-exchange interaction

In the study of interacting quantum spin chains, the ground state wavefunction carries information about the phases of matter that occur for different interaction parameters. In this case, a spin-1/2 chain with 3 interaction terms in the Hamiltonian--nearest neighbor, next nearest neighbor, and ring exchange, is investigated using entanglement entropy to map out a ground state phase diagram. In addition, further information can be obtained from the entanglement spectrum. Finally, preliminary investigations of the effects of an impurity on this triangular Heisenberg ladder are reported.