Dynamic conductivity and coherence peak inYBa2Cu3O7superconductors

Abstract

We measure directly both the real and imaginary parts of the sub-band-gap conductivity \ensuremath{\sigma} in ${\mathrm{YBa}}_{2}$${\mathrm{Cu}}_{3}$${\mathrm{O}}_{7}$ in the 15--80 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$ frequency range using coherent time-domain terahertz spectroscopy. We observe a peak in the real part ${\mathrm{\ensuremath{\sigma}}}_{1}$ similar to the coherence peak expected in an s-wave BCS superconductor. The absence of such a peak in NMR relaxation-rate experiments suggests that its origin lies in a strongly temperature-dependent inelastic-scattering rate rather in coherence factors.