LOW-ENERGY RAMAN CONTINUUM IN OVERDOPED Y1−xCaxBa2Cu3O7 FILMS

Abstract We investigate Y 1− x Ca x Ba 2 Cu 3 O 7 films on SrTiO 3 (100) substrates which are overdoped due to high oxygen contents and Ca substitution. The good in-plane orientation of the c -axis-oriented films allows us to study excitations with A 1g and B 1g symmetry. Our analysis reveals that at high doping the B 1g Raman-active phonon at 340 cm −1 behaves significantly differently from what has been observed so far, showing vanishing softening as well as strong broadening and no increasing intensity below T c . The observed behavior correlates with the fact that the energy of the so-called “2 Δ peak” that forms out of the continuum in B 1g symmetry is below the phonon energy at higher doping.