We study the energy spectrum of Bi2223 (Bi1.6Pb0.4Sr1.8Ca2.2Cu 3Ox) at high hydrostatic pressures by Andreev- and tunneling-spectroscopy methods. We determine the gap anisotropy in the basal ab plane and find the following values for the parameters Δ(φ): Δmax=42mV, and Δmin= 19.5 mV (Tc = 110 K and dTc/dP = 0.16 K/kbar). We detect an increase in the ratio R = 2Δmax/kTc with pressure P; for Bi2223 cuprate, dR/dP≈0.017 kbar-1. In the phonon-frequency region we detect a "softening," due to pressure, of the high-frequency part of the phonon spectrum corresponding to "breathing" modes of oxygen, as well as other optical modes of Cu-O. The characteristic frequencies of the spectrum for ℏΩ>60 mV are found to decrease, with increasing pressure, at a rate d ln(ℏΩ)/dP≈-6.5±0.5×10-3 kbar-1. This result explains the observed increase in the ratio 2Δ/kTc(P) in the model of strong electron-phonon interaction.
ASJC Scopus subject areas
- Physics and Astronomy(all)