Superconductivity-Induced Transfer of In-Plane Spectral Weight in Bi 2 Sr 2 CaCu 2 O 8+δ

Abstract

Optical data are reported on a spectral weight transfer over a broad frequency range of Bi ₂ Sr ₂ CaCu ₂ O _8+δ , when this material became superconducting. Using spectroscopic ellipsometry, we observed the removal of a small amount of spectral weight in a broad frequency band from 10 ⁴ cm ⁻¹ to at least 2 × 10 ⁴ cm ⁻¹ , due to the onset of superconductivity. We observed a blue shift of the ab -plane plasma frequency when the material became superconducting, indicating that the spectral weight was transferred to the infrared range. Our observations are in agreement with models in which superconductivity is accompanied by an increased charge carrier spectral weight. The measured spectral weight transfer is large enough to account for the condensation energy in these compounds.