Date:2012-01-09, 10:00am

Venue:Conference Hall 322, Science Building

Title: Spin Liquid Ground State of the Spin-1/2 Square J_1-J_2 Heisenberg Model

Speaker: Dr. Hong Yao

Stanford University

Abstract:We perform highly accurate density matrix renormalization group (DMRG) simulations to investigate the ground state properties of the spin-1/2 antiferromagnetic square lattice Heisenberg J_1-J_2 model. Based on studies of numerous long cylinders with circumferences of up to 10 lattice spacings, we obtain strong evidence for a topological quantum spin liquid state in the region 0.41less than J_2/J_1 less than 0.62, separating conventional Neel and striped antiferromagnetic states for smaller and larger J_2/J_1, respectively. The quantum spin liquid is characterized numerically by the absence of magnetic or valence bond solid order, and non-zero singlet and triplet energy gaps. Furthermore, we positively identify its topological nature by measuring a non-zero topological entanglement entropy, which is reasonably close to -log(2), and a non-trivial finite size dimerization effect depending upon the parity of the circumference of the cylinder.