Raman scattering in YBa2Cu4O8 and PrBa2Cu4O8:: Indications of pseudogap effects in nonsuperconducting PrBa2Cu4O8

By analysis of the Raman spectra of superconducting YBa2Cu4O8 (Y-124), we observe a suppression of low-energy electronic density of states that we link to changes in the Linewidth of the Ba-phonon mode. These effects occur at a temperature below 150 K, where also anomalies in resistivity and other physical properties take place. We argue that these changes in the Raman spectra of Y-124 are connected to the opening of a pseudogap. Analogous anomalies in resistivity and the Ba-phonon width in the nonsuperconducting homologue PrBa2Cu4O8 (Pr-124) below 150 K suggest that similar pseudogap effects can occur without a following transition to a superconducting state at st lower temperature.