Phonon density of states in YBa 2 Cu 3 O x

Temperature dependence of the EPR linewidth of Yb3+ ions in Y0.99Yb0.01Ba2Cu3OX (6 ≤ X ≤ 7) compounds: evidence for an anomaly near the superconducting transition

“…The anomaly of the spin-lattice relaxation rate near T C can be associated with the differences of the phonon spectrum of the YBaCuO host matrix in the superconducting and non-superconducting states. For example, as it is shown in [20], phonon spectra density of the superconducting sample with X = 6.95 at T = 80 K drastically differs from that at T = 290 K, while there is no great difference for the sample with X = 6.35. It is sensible for Yb 3+ ions because practically whole phonon spectrum is involved into the usual Raman relaxation process.…”

“…The line broadening of Er 3+ ions with temperature is caused by the two-step resonance fluorescence SLR process. The phonon density for the phonons with energy of 9-12 meV (corresponding to Stark exitation energy Δ for Er 3+ ) involved into the relaxation mechanism is approximately constant below and above T C [20].…”

“…For example, as it is shown in [20], phonon spectra density of the superconducting sample with X = 6.95 at T = 80 K drastically differs from that at T = 290 K, while there is no great difference for the sample with X = 6.35. It is sensible for Yb 3+ ions because practically whole phonon spectrum is involved into the usual Raman relaxation process.…”

“…It is sensible for Yb 3+ ions because practically whole phonon spectrum is involved into the usual Raman relaxation process. In addition, we have to note again that a local peak in the vicinity of 40 meV (≈ 460 K) also observed in [20] for the superconducting species.…”