ARPES EVIDENCE FOR A QUASIPARTICLE LIQUID IN OVERDOPEDBi2Sr2CaCu2O8+δ

High resolution angle-resolved photoemission spectroscopy of highly overdopedBi2Sr2CaCu2O8+δwithTc= 51Kindicates that the basic transport processes in this material are fundamentally different from both the lesser-doped cuprates and model metallic compounds. The overdoped sample has sharp ARPES peaks at the Fermi energy throughout the Brillouin zone even in the normal state, unlike the lesser-doped compounds. In particular, the spectra near the(π, 0)point show the presence of a sharp peak well aboveTc. The ARPES line shapes, and thus the self-energy, at a given energy are almost independent ofk. 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 overdopedBi2Sr2CaCu2O8+δis 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 a typical metal.