ARPES evidence for a Quasiparticle Liquid in overdoped Bi&k2CaCu208+d

High resolution angle-resolved photoemission spectroscopy of highly overdoped Bi2Sr2CaCu208+6with a T. = 5lK indicates that the basic transport processes in this material are fundamentally different from both the lesser doped cuprates as well as model metallic compounds. The overdoped sample has sharp AWES peaks at the Fermi energy throughout the Brillouin zone even in the normal state, unlike the lesser-doped compounds. In particular, the spectra near (z,O) point show the presence of a sharp peak well above l“.. The ARPES lineshapes, and thus the self energy, at a given energy are almost independent of k. Further, the quasiparticle scattering rate at the Fermi energy seems to be closely tied to direct resistivity measurements. This leads us to the conclusion that overdoped Bi2Sr2CaCu208+6is best described as a quasiparticle liquid. However, the energy dependence of the scattering rates is quite similar to that found in the lesser-doped compounds and quite different from that seen in atypical metal.