In-plane polarized collective modes in detwinned YBa2Cu3O6.95 observed by spectral ellipsometry

Abstract The in-plane dielectric response of detwinned YBa 2 Cu 3 O 6.95 has been studied by far-infared ellipsometry. A surprisingly large number of in-plane polarized modes are observed. Some of them correspond to pure phonon modes. Others possess a large electronic contribution which strongly increases in the superconducting state. The free carrier response and the collective modes exhibit a pronounced a – b anisotropy. We discuss our results in terms of a charge density wave state in the 1-D CuO chains and induced charge density fluctuations within the 2-D CuO 2 planes.