Ultrasonic velocity studies on elastic properties and electron-phonon coupling in EuBa2Cu₁₃07‐δ superconductors / Nurul Nadia Muhamad

Longitudinal and shear ultrasonic velocities in Al substituted EuBa2(Cui-xAlx)307_5 (x = 0, 0 (quenched), 0.06 and 0.10) superconductors have been measured using the pulsed-echo-overlap (PEO) method at frequency 9MHz in the temperature ranges of 80 K-280 K (longitudinal) and 80 K-220 K (shear). Substitution of Al caused the step-like anomaly strongly suppressed and strongly indicates involvement of Cu-0 chains at the Cu-site of RE123. For x = 0, a step-like elastic anomaly indicate sudden lattice stiffening was observed at temperature 260 K. The characteristic Debye temperature, 0D and electron-phonon coupling constant were estimated using the standard BCS theory as well as two-dimensional van Hove scenario. The van Hove electron-phonon coupling constant is in the range of WH = 0.030-0.050 and Al substitution also has effect of lowering the calculated electron-phonon coupling constant (X). These finding shows that, the step-like elastic anomaly occurred when substitution of Al3+ into Cu-0 chain site and effectively destroys the oxygen ordering.