The superconducting and normal state gaps in YBa2Cu4O8: an electronic Raman scattering study

Raman spectra of a high quality YBa2Cu4O8 single crystal grown in inert BaZrO3 crucible have been measured and changes in the electronic background have been studied at temperatures from 10 to 300 K. No temperature dependence has been observed in the XY (B2g) geometry. In X′Y′ (B1g) a clear superconductivity-related depletion of the electronic scattering at low frequencies is observed below Tc, from which we determine a maximum gap of approximately 650 cm−1. Furthermore, there is a depletion which takes place over a much larger frequency range and appears at higher temperature, which we associate with a normal-state gap.