Direct observation of charge order in underdoped and optimally doped Bi2(Sr,La)2CuO6+delta by resonant inelastic x-ray scattering

Charge order in underdoped and optimally doped high-Tc superconductors Bi2Sr2-xLaxCuO6+? (Bi2201) is investigated by Cu L3 edge resonant inelastic x-ray scattering. We have directly observed charge density modulation in the optimally doped Bi2201 at momentum transfer Q?0.23 reciprocal lattice units, with smaller intensity and correlation length with respect to the underdoped sample. This demonstrates the short-range charge order in Bi2201 persists up to optimal doping, as in other hole-doped cuprates. We explored the nodal (diagonal) direction and found no charge order peak, confirming that charge density modulates only along the Cu-O bond directions. We measured the out-of-plane dependence of charge order, finding a flat response and no maxima at half integer L values. This suggests there is no out-of-plane phase correlation in single layer Bi2201, at variance from YBa2Cu3O6+x and La2-x(Ba,Sr)xCuO4. Combining our results with data from the literature we assess that charge order in Bi2201 exists in a large doping range across the phase diagram, i.e., 0.07p0.16, demonstrating thereby that it is intimately entangled with the antiferromagnetic background, the pseudogap, and superconductivity.