Wigner Lattice Order, Collective Mode, and Superconductivity in La1.985Sr0.015CuO4+delta System

We have studied far-infrared charge dynamics of Sr- and O- co-doped La1.985Sr0.015CuO4+delta with delta = 0.024 (p = 0.063 per Cu) and delta = 0.032 (p = 0.07). We found that two-dimensional Wigner lattice order is the ground state of cuprates away from half-filling. We found that the presence of 2D Wigner lattice and the pinned Goldstone mode is essential for the cuprate physics and superconductivity. We propose that all the high Tc physics are based on the existence of these peculiar 2D electron lattices.