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

Abstract

We performed STM/STS experiments at 8 K in Bi2Sr1.7R0.3CuO6+δ (R-Bi2201) systems that had optimal (OP) hole-doping levels (∼0.17) but different Tc values, 35 K for R = La and 20 K 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 ΔPG increases from ∼30 to ∼60 meV, the nodal SCG size ΔSC seems to decrease from ∼7 to ∼4 meV, and the pairing gap amplitude Δ0 or d-wave gap size at the antinodes is almost unchanged (Δ0 ∼ 15 meV). These gap sizes for OP doping in Eu-Bi2201 are comparable to those for an underdoping level of ∼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...