Closing of the pseudogap in Sr-doped and Nd-codoped lanthanum cuprate (LSCO, Nd-LSCO)

Doping of La_2CuO_4 and La_{1.6}Nd_{0.4}CuO_4 with Sr gives rise to holes that locate pairwise at lattice-site O atoms. Such O atoms reside as lattice defects in the CuO_2 planes if the doping level x is below a watershed value, x < x^, but also the bracketing LaO layers if x > x^. The O atoms form a 2D charge order of incommensurability q^{CuO_2}(x) and q^{LaO}(x). At the doping x* (quantum critical point) that causes the closing of the pseudogap at T=0, q^{CuO_2}(x*) = 2q^{LaO}(x*) holds.