Carrier relaxation, pseudogap, and superconducting gap in high-Tccuprates: A Raman scattering study

Abstract

We describe the results of electronic Raman-scattering experiments in differently doped single crystals of YBa 2 Cu 3 O 6ϩx and Bi 2 Sr 2 (Ca x Y 1Ϫx )Cu 2 O 8 . The data in antiferromagnetic insulating samples suggest that at least the low-energy parts of the spectra of metallic samples originate predominantly from excitations of free carriers. We therefore propose an analysis of the data in terms of a memory function approach which has been introduced earlier for the current response. Dynamical scattering rates ⌫()ϭ1/() and mass-enhancement factors 1ϩ()ϭm*()/m of the carriers are obtained. It is found that a strong polarization dependence of the carrier lifetime develops towards low doping. In B 2g (xy) symmetry selecting predominantly electrons with momenta along the diagonals of the CuO 2 planes the Raman data compare well with the results obtained from dc and dynamical transport. In B 1g (x 2 Ϫy 2 ) symmetry projecting out momenta along the Cu-O bonds the dc scattering rates of underdoped materials become temperature independent and considerably larger than in B 2g symmetry. This increasing anisotropy is accompanied by a loss of spectral weight in B 2g symmetry in the range between the superconducting transition at T c and a characteristic temperature T* of the order of room temperature which compares well with the pseudogap temperature found in other experiments. The energy range affected by the pseudogap is doping and temperature independent. The integrated spectral loss is approximately 25% in underdoped samples and becomes much weaker towards higher carrier concentration. In underdoped samples, superconductivity-related features in the spectra can be observed only in B 2g symmetry. The peak frequencies scale with T c . We do not find a direct relation between the pseudogap and the superconducting gap.

Raman scattering versus infrared conductivity: Evidence for one-dimensional conduction inLa2−xSrxVenturini1, Zhang2, Hackl3 et al. 2002Phys. Rev. BSelf Cite449310View full textAdd to dashboardCite

“…Similarly as in previous studies no pair-breaking feature can be observed below T c at this doping level. 1,4,9 Completely unexpectedly, however, the low-energy response increases strongly for T < 100 K. Although the spectra are measured down to 15 cm −1 the linear decrease (inevitably present for causality) towards zero energy cannot be resolved any more. Consequently, the lifetime must become very long and exceed the one observed at B 2g symmetry by far.…”

“…At high energies,hω ≥ 400 cm −1 , the spectra are qualitatively similar to earlier results 4 and to those measured in Y123 and Bi2212. 1,8,9 Up to approximately 1500 cm −1 the continuum is essentially constant in B 2g symmetry ( Fig. 1 (b)) and increases linearly in B 1g symmetry ( Fig.…”

“…In spite of the strong correlations in high-T c superconductors such as YBa 2 Cu 3 O 6+y (Y123) or Bi 2 Sr 2 CaCu 2 O 8+y (Bi2212) the electron dynamics derived from IR and Raman spectroscopies agree quite reasonably as long as the selection rules are properly taken into account. 1 On the other hand, in low-T c cuprates such as La 2−x Sr x CuO 4+y (LSCO) the far-infrared conductivity σ(ω, T ) exhibits strong additional contributions 2,3 peaked between 100 and 500 cm −1 which do not have a counterpart in the Raman spectra. 4 In Bi 2 Sr 2 CuO 6 (Bi2201) a similar peak in σ(ω, T ) has been observed at low temperatures which is well separated from a conventional Drude term 5 having a width of only a few cm −1 .…”

“…In lowest order one obtains χ ′′ (ω, T ) ∝ ωσ(ω, T ) for the Raman response 1,17 . Hence, we determine…”

Fermi arcs in cuprate superconductors: Tracking the pseudogap belowTcand aboveT*

“…Below T c the SC gap opens up on the Fermi arcs thereby obscuring the details of how the PG further evolves with T , and in particular whether the PG itself becomes nodal at T = 0. Raman scattering allows the PG and SC gaps to be separately probed via the antinodal (B 1g ) and nodal (B 2g ) Raman response [10,11,12]. We calculate these for Bi-2212 using an ARPES derived energy-momentum dispersion.…”