Ling WANG
University of Vienna
Abstract: The spin 1/2 J1-J2 Antiferromagnetic Heisenberg model on square lattice has raised great attention for its intriguing quantum phase transition and possible exotic phases. Due to its frustrated nature, a large scale low temperature quantum Monte Carlo study is prohibited. A tensor network variational wavefunction ansatz, on the other hand, suites very well to describe the strongly correlated quantum many body systems, and the tensor network method is free of the negative sign problem due to its variational nature. We thus explore the ground state phase diagram of this model via a tensor network approach.
Using a recently proposed cluster update algorithm for tensor network states, we are able to access the tensor network ground state with a virtual bond dimension D up to 9. We observed a second order quantum phase transition from an antiferromagnetic ordered phase to a paramagnetic disordered phase at a critical point J2_c = 0.47. The paramagnetic disordered phase preserves all symmetries of the Hamiltonian and does not have any local order. A spin liquid nature of this disordered paramagnetic state is very likely. We further studied the topological entanglement entropy of the disordered paramagnetic phase and discovered that it belongs to the Z2 topological class.
References: 
1. L. Wang and F. Verstaete, arXiv:1110.4362.
2. L. Wang, Z.-C. Gu, X.-G. Wen, A. W. Sandvik, and F. Verstraete, work in preparation.

Location: 606 Conference Room
Date and time: Dec 9, 2011   14:30