Conference

In underdoped cuprate superconductors, a rich competition occurs between superconductivity and charge density wave order (CDW). Under debate, however, is whether rotational symmetry breaking (nematicity) also plays a central role -- whether it occurs intrinsically and generically or merely as a consequence of other orders. Here we employ resonant x-ray scattering in stripe-ordered (La,X)2CuO4 to probe the relationship between electronic nematicity of the Cu 3d orbitals, structural orthorhombicity of the (La,X)2O4 layers and CDW order. We find distinct temperature dependences of the structural orthorhombicity and the electronic nematicity, with the electronic nematicity, but no structural orthorhombicity enhancement below the onset of CDW order. These results indicate electronic nematicity is an order parameter that is distinct from a purely structural order parameter in underdoped cuprates.

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.