Observation of the predicted charge collective mode of the T _c = 45 K superconducting phase of La _2CuO _(4+δ)

摘要

We report the far-infrared (far-IR) observation of the Goldstone mode at ～ 72 cm ~(-1) (～ 9 meV) predicted to exist in the superconducting phase of the transition temperature (T c) at 45 K in the La _2CuO _4-based superconductors. Our observation furthers the experimental support for the two-component picture where the localized charge texture, formed at a specific planar hole density (P _(pl)), is tied to the high temperature super-conductivity (HTS) at T _c = 15 K, 30 K, and 45 K in a hierarchical fashion at the so-called "magic" doping level at P _(pl) = 1/16, 2/16, and 3/16 respectively.