Anisotropies in insulating La(2-x)Sr(x)CuO(4): Angle-resolved photoemission and optical absorption

Due to the orthorhombic distortion of the lattice, the electronic hopping integrals along the a and b diagonals, the orthorhombic directions, are slightly different. We calculate their difference in the local density approximation and find t(a)'-t(b)'approximate to 8 meV. We argue that electron correlations in the insulating phase of La(2-x)Sr(x)CuO(4), i.e., at doping x <= 0.055, dramatically enhance the (t(a)'-t(b)')-splitting between the a- and b-hole valleys. In particular, we predict that the intensity of both angle-resolved photoemission and optical absorption is very different for the a- and b-nodal points.