Out-of-Plane Disorder Effects on the Energy Gaps and Electronic Charge Order in Bi2Sr1.7R0.3CuO6+δ (R = La and Eu)

We performed STM/STS experiments at 8K in Bi2Sr1.7R0.3CuO6+delta (R-Bi2201) systems that had optimal (OP) holedoping levels (similar to 0.17) but different T-c values, 35K for R = La and 20K for R = Eu, and examined out-of-plane disorder effects on the superconducting (SC) gap (SCG) and the pseudogap (PG) which is associated with the so-called "checkerboard charge order" (CCO). As out-of-plane disorders are strengthened by replacing La with Eu in OP R-Bi2201, the antinodal PG size Delta(PG) increases from similar to 30 to similar to 60 meV, the nodal SCG size Delta(SC) seems to decrease from similar to 7 to similar to 4 meV, and the pairing gap amplitude Delta(0) or d-wave gap size at the antinodes is almost unchanged (Delta(0) similar to 15 meV). These gap sizes for OP doping in Eu-Bi2201 are comparable to those for an underdoping level of similar to 0.1 in La-Bi2201. Although out-of-plane disorders strongly affect the electronic system of the Cu-O plane, they have no effect on the period of the CCO, which is five times the lattice constant (5a) along the Cu-O bond directions for OP doping and 4a for p similar to 0.1. We suggest that the concentration of holes doped into the Cu-O plane may be an essential factor for determining the period of the CCO.