Charge order and two pseudogap structures of Bi-based high-T_c superconductor studied by STM・STS

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To investigate the nature of the charge order associated with the large pseudogap, dI/dV images as well as LDOS were measured by using STM/STS technique on Bi-based high Tc cuprates. The present work leads to the following findings; 1) the charge order coexists with the quasiparticle interference patterns at low energies within the energy gap, 2) the period of the charge order tends to increase discontinuously by multiples of a lattice constant as the doping level is increased, and 3) the doping level is enhanced in the bright region of the charge order compared with the dark region. These results indicate that the charge order will originate in the redistribution of holes within the Cu-O planes, as that illustrated in the stripe model. Relationship between the small pseudogap and the superconductivity was also examined in the present work.