Quasiparticle damping in Bi2Sr2CaCu2O8 and Bi2Sr2CuO6

Abstract

The low-frequency conductivity ${\mathrm{\sigma }}_1$(ω) of ${\mathrm{Bi}}_2$ ${\mathrm{Sr}}_2$ ${\mathrm{CaCu}}_2$ ${\mathrm{O}}_8$ has a Drude-like component below ${\mathit{T}}_{\mathit{c}}$. Interpreting the width of this component as the quasiparticle relaxation rate (${\mathrm{\tau }}^{\mathrm{-}1}$), we find that ${\mathrm{\tau }}^{\mathrm{-}1}$ decreases dramatically just below ${\mathit{T}}_{\mathit{c}}$, in sharp contrast with the T-linear ${\mathrm{\tau }}^{\mathrm{-}1}$ above ${\mathit{T}}_{\mathit{c}}$ and ${\mathrm{Bi}}_2$ ${\mathrm{Sr}}_2$ ${\mathrm{CuO}}_6$. This decrease causes a peak in ${\mathrm{\sigma }}_1$(ω→0,T) for T just below ${\mathit{T}}_{\mathit{c}}$, a peak which is due to the scattering rate and not to pair coherence effects, consistent with the lack of a coherence peak in the NMR relaxation rate. This result implies that the excitations which scatter the carriers are suppressed below ${\mathit{T}}_{\mathit{c}}$.