Evidence for a pseudogap in underdoped $Bi_2Sr_2CaCu_2O_{8+\delta}$ and $YBa_2Cu_3O_{6.50}$ from in-plane optical conductivity measurements

TL;DR

This study provides optical evidence for the pseudogap in underdoped cuprates, revealing characteristic features in the optical self-energy that distinguish underdoped from optimally doped and overdoped samples.

Contribution

The paper introduces a theoretical analysis of optical self-energy data that identifies clear signatures of the pseudogap in underdoped cuprates, advancing understanding of pseudogap phenomena.

Findings

Detection of a pileup in density of states above the pseudogap energy

Rapid increase in optical scattering rate below the pseudogap

Distinct features in optical self-energy indicating pseudogap presence

Abstract

The real part of the in-plane optical self-energy data in underdoped Bi$_{2}$Sr$_{2}$CaCu$_{2}$O$_{8+\delta}$ (Bi-2212) and ortho II YBa$_{2}$Cu$_{3}$O$_{6.5}$ contains new and important information on the pseudogap. Using a theoretical model approach we find that the density of state lost below the pseudogap $\Delta_{pg}$ is accompanied with a pileup just above this energy. The pileup along with a sharp mode in the bosonic spectral function leads to an unusually rapid increase in the optical scattering rate and a characteristically sloped peak in the real part of the optical self-energy. These features are not found in optimally doped and overdoped samples and represent a clearest signature so far of the opening of a pseudogap in the in-plane optical conductivity.