Electronic Raman scattering in YBa2Cu4O8 at high pressure

We have investigated the electronic Raman scattering in YBa2Cu4O8 at hydrostatic pressures up to 9 GPa. At pressures below 1.5 GPa, the continuum in the normal state is strongly temperature dependent in all three polarization configurations measured. This temperature dependence follows a Bose-Einstein form, consistent with the earlier report of Donovan et al. With increasing pressure, the temperature dependence implied by the Bose-Einstein factor gradually decreases, and above 6 GPa the electronic continuum of the normal state becomes very weakly temperature dependent in all three configurations, an effect which is also observed in YBa2Cu3O7 at ambient pressure. With increasing pressure, YBa2Cu4O8 is generally believed to be tuned from underdoped to optimally doped. Given this scenario, we can explain our results within a model recently proposed by Varma, who suggests there is a crossover from the Fermi-Liquid to the so-called Marginal-Fermi-Liquid when the superconducting cuprates are tuned toward optimal doping. Additionally, we report on the pressure dependent rearrangement of the continuum which occurs below T-c. Copyright (C) 1996 Elsevier Science Ltd.