Low frequency phonon model in YxPr1−xBa2Cu3O7 system

In order to explore how important the electron–phonon coupling is in high Tc superconductors, we calculate the phonon frequencies at Gamma-point of the YxPr1−xBa2Cu3O7 system by considering a special local structure in the YxPr1−xBa2Cu3O7, which is so called “fixed triangle”. It is found that a low frequency mode is possibly caused by the “fixed triangle” and roughly matches the experiment of Raman spectrum, which suggests that the coupling...