STM/STS studies for interplane disorder effects on the electronic states of the Cu–O plane in Bi2201

STM/STS experiments have been performed in Bi2Sr1.7R0.3CuO6+δ (R-Bi2201) systems with R = La and Eu, which are of a nearly optimal doping level po but have different Tc values, 35 K and 20 K, respectively, to examine interplane disorder effects on the superconducting (SC) gap and the pseudogap (PG) that is accompanied by a checkerboard-type charge order (CCO). We report that as interplane disorders are strengthened by replacing La with Eu in optimal Bi2201, the antinodal PG size Δ∗ increases from ∼ 30meV to ∼ 60meV, which is comparable to the value for an underdoping level p∕po ∼ 0.5 in La-Bi2201. On the other hand, the period of CCO in optimal Eu-Bi2201 is the same as in optimal La-Bi2201, about five times lattice constant ∼ 5a along the Cu–O bond directions; it remains unchanged even if the PG develops markedly to the same degree as for p∕po ∼ 0.5 in La-Bi2201, whose period is ∼ 4a.