Pseudogap in Cuprates by Electronic Raman Scattering

TL;DR

This study uses electronic Raman scattering to investigate the pseudogap in Bi-2212 cuprate superconductors, revealing its distinct features in different momentum regions and its competition with the superconducting gap.

Contribution

It provides detailed experimental evidence of the pseudogap's behavior in both antinodal and nodal regions, highlighting its different structure and interaction with superconductivity.

Findings

Pseudogap appears in underdoped regime with depletion in Raman spectra.

Pseudogap energy is higher in B2g than in B1g spectra.

Nodal quasiparticle spectral weight increases with underdoping.

Abstract

We present Raman experiments on underdoped and overdoped Bi2Sr2CaCu2O(8+d) (Bi-2212) single crystals. We reveal the pseudogap in the electronic Raman spectra in the B1g and B2g geometries. In these geometries we probe respectively, the antinodal (AN) and nodal (N) regions corresponding to the principal axes and the diagonal of the Brillouin zone. The pseudogap appears in underdoped regime and manifests itself in the B1g spectra by a strong depletion of the low energy electronic continuum as the temperature decreases. We define a temperature T* below which the depletion appears and the pseudogap energy, omegaPG the energy at which the depeletion closes. The pseudogap is also present in the B2g spectra but the depletion opens at higher energy than in the B1g spectra. We observe the creation of new electronic states inside the depletion as we enter the superconducting phase. This leads us to conclude (as proposed by S. Sakai et al.) that the pseudogap has a different structure than the superconducting gap and competes with it. We show that the nodal quasiparticle dynamic is very robust and almost insensitive to the pseudogap phase contrary to the antinodal quasiparticle dynamic. We finally reveal, in contrast to what it is usually admitted,an increase of the nodal quasiparticle spectral weight with underdoping. We interpret this result as the consequence of a possible Fermi surface disturbances in the doping range p=0.1-0.2.