paper

Spin Liquid Ground State of the Spin-1/2 Square - Heisenberg Model

arXiv:1112.2241 · doi:10.1103/PhysRevB.86.024424

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 - model. Based on studies of numerous long cylinders with circumferences of up to 14 lattice spacings, we obtain strong evidence for a topological quantum spin liquid state in the region , separating conventional Néel and striped antiferromagnetic states for smaller and larger , 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 , extremely close to (expected for a quantum spin liquid) and a non-trivial finite size dimerization effect depending upon the parity of the circumference of the cylinder. We also point out that a valence bond solid, and indeed any discrete symmetry breaking state, would be expected to show a constant correction to the entanglement entropy of {\sl opposite} sign to the topological entanglement entropy.

14 pages, 6 figures in the main text. Accuracy improved and missing references added

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