Density of States Modulations in Pseudo Gap of Bi2Sr2CaCu2O8+δ

Pseudo-Gap (PG) phase of the cuprates is believed to hold a key to the understanding of the mechanism of high Tc superconductivity. Recently, QPI, SDW, and PDW modulations were observed in BSCCO and especially CDW phase in PG have been reported. These modulations' detailed origin, however, is still not fully understood let alone the relation to the superconductivity. Our STM study on Bi2Sr_{2CaCu2O8+δ in PG phase revealed a density of states (DOS) modulation with properties different from conventional CDW or quasiparticle interference (QPI) : particle - hole asymmetric dispersion and non-locality. In this talk, we will present a quantitative analysis to estimate the correlation length of these density modulations in real space as well as momentum space and their possible origin. We will also discuss the relation of our observation to previously reported CDW and QPI features.}