Interplay of Lattice and Charge Density Waves in Cuprates

A now famous charge density wave (CDW) state emerges with moderate hole doping into CuO₂ layer of cuprates. To describe the CDW state, two different pictures on two sides of electron-phonon coupling strength are proposed. In the weak coupling limit, the CDW state occurs when Fermi surface are scattered by the phonon with the same wavevector Q. While in the strong coupling case, larger lattice distortion amplitude maximally separates the strong interacting charges in real-space which is also indicated by the prominent broadening width of the Kohn anomaly around the same wavevector Q. Hence, in the simplest case of 1-dimensional state, one might expect Q = p for a strong coupling CDW and Q ∝1 - p for a weak coupling CDW. However, in hole-dope Bi₂Sr₂CaCu₂O₈ when p «1, the dependence of Q(p) observed remains constant until the CDW state disappears at p ≥ 0.2. We attempt to explore the issue by combining lattice displacement and CDW imaging.