Phonon density of states of superconducting YBa2Cu3O7 and the nonsuperconducting analog YBa2Cu3O6

Derivative Analysis of the High Temperature Superconducting Transition

The shape of the normalized temperature derivative of the dc susceptibility provides useful information about superconducting materials. We propose that the position of the derivative peak be defined as the transition temperature Tc and the width of this peak define its sharpness.

Laser Raman evidence for enhanced electron–phonon coupling in a Y–Ba–Cu-oxide superconductor below T c : an application of the maximum entropy method of spectral estimation

This report discusses Raman spectra, recorded at various temperatures from 4.2 to 100 K, of the high-temperature oxidic superconducting material YBa 2 Cu 3 O 7 ( T c = 90 K). By utilizing the maximum entropy method (MEM) the Raman bands were separated from the luminescent background. Our results clearly demonstrate significant enhancement of Raman activity, indicative of strong electron–phonon coupling, below the superconducting transition temperature, together with low-temperature ordering of the copper ions in their lattice sites. Several bands may also be attributed to defects of the oxygen lattice, some of which disappear as the reordering occurs.