Possibility of Pomeranchuk instability in staggered flux state

In connection with the symmetry-breaking phenomena found in cuprate superconductors, the instability toward x-y and (x + y)-(x - y) anisotropy (Pomeranchuk instability) is studied for a strongly correlated Hubbard model (U/t = 12) on a square lattice with the next-nearest-neighbor transfer t′ using a variational Monte Carlo method. As a variational function, a staggered flux state Ψ_SF is considered, which is a candidate for the pseudogap state in cuprates. Ψ_SF is stabilized in a underdoped regime and reduced to the normal state (projected Fermi sea) for larger doping area. By analyzing Ψ_SF for t′/t = 0, ±0.3, we argue that the appearance of Pomeranchuk instability is limited to the normal state with t′/t = 0 and 0.08 ≤ δ ≤ 0.20 (σ: doping rate) in the x-y anisotropy. Band-renormalization effects (Fermi-surface modification) owing to strong correlations play a crucial role for the argument.