Particle-hole asymmetric QPI in the pseudogap phase of underdoped Bi-2212

Quasi-Particle Interference (QPI) measured by STM revealed many interesting phenomena in Correlated Electron Systems. Particle-hole (p-h) symmetric QPI observed in the superconducting Bi$_{2}$Sr$_{2}$CaCu$_{2}$O$_{8+\delta}$ disappears around the reduced zone boundary [1], while p-h asymmetric QPI's on non-superconducting Sr$_{3}$Ru$_{2}$O$_{7}$ [2] and Ca(Fe$_{x}$Co$_{1-x}$)$_{2}$As$_{2}$ [3] identified dominant band structures, suggesting electronic nature of the nematic phases. In light of these discoveries, here we report the observation of p-h asymmetric QPI of underdoped Bi$_{2}$Sr$_{2}$CaCu$_{2}$O$_{8+\delta}$ in the pseudogap phase continuously dispersing through E$_{F}$. The Fermi velocity measured from this dispersion is $\sim$0.12$\times$10$^{6}$ m/s. We will discuss the possible origin and implications by comparing its symmetry and dispersion using theoretical model and currently available experimental data from other probes.\\[4pt] [1] Y. Kohsaka et al., Nature 454, 1072 (2008)\\[0pt] [2] Jinho Lee et al., Nature Physics 5, 800 (2009)\\[0pt] [3] Chuang et al., Science 327, 181 (2010)