Conference

The ground state phase diagram of spin-1/2 J1-J2 antiferromagnetic Heisenberg model on square lattice around the maximally frustrated regime (J2~0.5J1) has been debated for decades. I will discuss some progresses on this old problem based on recent numerical results from density matrix renormalization group(DMRG) and tensor product states algorithms.

The most interesting states of the cuprate compounds are not the superconductors with high critical temperatures. Instead, the novelty lies primarily in the higher temperature metallic "normal" states from which the superconductors descend, and in competing low temperature states with density wave order. I will review recent experimental and theoretical progress in understanding these states. The experimental evidence is compatible with the presence of a metal with topological order in the 'pseudogap' regime of low carrier density.