Effect of the metal-superconductor phase transition and Co doping on the phonon spectra of YBa2Cu3O7-δ

✍ Scribed by H.S. Obhi; E.K.H. Salje

• Publisher: Elsevier Science
• Year: 1990
• Tongue: English
• Weight: 444 KB
• Volume: 171
• Category: Article
• ISSN: 0921-4534
• DOI: 10.1016/0921-4534(90)90271-f

✦ Synopsis

The infrared-active phonon spectra of YBa2 ( CoxCu ~ _ x ) 307 _ ~ ( 0 < x < 0.07 ) have been studied between 35 K and room temperature. The mode near 580 cm-~ depends sensitively on Co doping and renormalizes due to the metal-superconductor phase transition. The excess phonon frequency and absorption cross-section scale as the square of the order parameter in the superconducting phase. This temperature evolution is in accordance with Landau-Ginzburg theory including saturation effects, which is numerically similar to BCS behaviour. Phonon contributions to the specific heat as a function of Co content correlate closely with observed anomalies in calorimetric measurements, indicating that phonons contribute intrinsically to the transition mechanism, e.g. via Bose condensation of structural bipolarons. The growth of a phonon doublet at ~ 657 cm-~ is attributed to effects of Co doping and discussed in view of the orthorhombic to tetragonal structural phase transitions at x~0.025 and J~0.