Quantum spin liquid near Mott transition with fermionized π-vortices.

In this paper, we study the non-magnetic insulator state near Mott transition of 2D π-flux Hubbard model on square lattice and find that such non-magnetic insulator state is quantum spin liquid state with nodal fermionic excitations - nodal spin liquid (NSL). When there exists small easy-plane anisotropic energy, the ground state becomes Z topological spin liquid (TSL) with full gapped excitations. The U(1) × U(1) mutual-Chern-Simons (MCS) theory is obtained to describe the low energy physics of NSL and TSL. [ABSTRACT FROM AUTHOR]