The in-plane electrodynamics of the superconductivity in Bi2Sr2CaCu2O8+d: energy scales and spectral weight distribution

TL;DR

This study investigates the in-plane electrodynamics of Bi2Sr2CaCu2O8+d superconductors across doping levels, revealing different spectral weight transfer mechanisms and energy scales involved in the superconducting transition.

Contribution

It provides detailed measurements of optical conductivity and spectral weight transfer in Bi-2212, highlighting the differences between underdoped and overdoped regimes and addressing the kinetic energy change.

Findings

Spectral weight shifts from below 60 meV in overdoped samples.

Spectral weight shifts up to 2 eV in underdoped samples.

Kinetic energy change in superconducting transition is about 1 meV.

Abstract

The in-plane infrared and visible (3 meV-3 eV) reflectivity of Bi2Sr2CaCu2O8+d (Bi-2212) thin films is measured between 300 K and 10 K for different doping levels with unprecedented accuracy. The optical conductivity is derived through an accurate fitting procedure. We study the transfer of spectral weight from finite energy into the superfluid as the system becomes superconducting. In the over-doped regime, the superfluid develops at the expense of states lying below 60 meV, a conventional energy of the order of a few times the superconducting gap. In the underdoped regime, spectral weight is removed from up to 2 eV, far beyond any conventional scale. The intraband spectral weight change between the normal and superconducting state, if analyzed in terms of a change of kinetic energy is ~1 meV. Compared to the condensation energy, this figure addresses the issue of a kinetic energy driven mechanism.