Abstract

The superconducting gap represents a key parameter in the understanding of new high temperature superconductors. The magnitude of the gap relative to the superconducting transition temperature will determine the viability of a strong or a weak coupling theory. In spite of the importance of this parameter there is wide disagreement between infrared and tunneling results on its magnitude. We present Raman determinations of the superconducting gap in thallium 2223 single crystals which have the highest known transition temperature. Raman spectra taken from several well-characterized superconducting Tl₂Ca₂Ba₂Cu₃O₁₀ (2223) single crystals (T_c = 105 K) display the characteristic phonon spectrum of the 2223 phase on top of a broad background continuum interpreted as electronic scattering. The electronic scattering continuum decreases substantially below T_c for frequency shifts smaller than 400 cm^-1, indicating the formation of a superconducting gap. The gap does not show the expected abrupt onset but a linearly rising electronic scattering background possibly indicating a distribution of gaps or the presence of electronic excitations within the gap.

© 1989 Optical Society of America