Doping dependence of the pseudogap in theabplane infrared spectra ofBi2Sr2Ca

Abstract

The ab plane optical spectrum of underdoped Bi 2 Sr 2 Ca 1Ϫx Y x Cu 2 O 8ϩ␦ has been studied as a function of temperature. The gaplike suppression in scattering rate 1/͑͒ observed below and above T c is found to be related to the shoulder structure in reflectivity R() and the broad peak or downward suppression from Drude-like shape in conductivity 1 (). We conclude that the superconducting gap, which is visible in 1 (), evolves smoothly into the pseudogap. The results obtained are consistent with recent electron tunneling and photoemission measurements. ͓S0163-1829͑99͒05201-7͔

The pseudogap in La_2–<i>x</i>Sr_<i>x</i>CuO₄: A Raman viewpoint

“…The results shown in Fig. 5 are consistent with the depression of low-energy scattering rates that have been obtained from FIR spectra [8][9][10]. This observation is also consistent with the suggestion [3,5,27] that FIR spectra are determined by the properties of B 2g or "cold" quasiparticles.…”

“…The spectra also show that this spectral weight appears to be transferred from the lowenergies region to the higher energy (ω > 1500 cm −1 ) spectral region normally occupied by multi-magnon scattering. The observed temperature dependence of the scattered intensity in the B 1g channel is found to be correlated with a depression of the scattering rate Γ(ω,T) in the B 2g channel, similar to that derived from measurements [8][9][10] of the infrared conductivity. The suppression of Γ(ω,T) is characterized by an energy scale ω Γ (x) ∼ 800 cm −1 which is the same [2,3] as the energy scale associated with the doping induced depletion of spectral weight.…”

“…1 for the x = 0.08, 0.11, 0.13 crystals are in qualitative agreement with estimates obtained for T * from FIR [8] and NMR [16] measurements in La214. Our results thus suggest that the PG is reflected in NMR [16,17] and FIR [8][9][10] measurements only in terms of the weaker temperature dependent depletion that occurs at T * . The results also provide a reconciliation with specific heat measurements [11], in which no clear evidence for T * is obtained.…”

“…In an attempt to resolve these questions many recent experiments have attempted to determine the energy scale E g , doping dependence, and symmetry associated with the PG. The experimental situation remains unclear, however, in that Raman [2][3][4][5][6][7], far infrared reflectivity (FIR) [8][9][10], specific heat [11] and some recent [12] angle resolved photoemission spectroscopy (ARPES) experiments yield E g ∼ J, where J is the antiferromagnetic (AFM) exchange energy, while tunneling [13] and earlier ARPES experiments [14,15] on Bi 2 Sr 2 CaCu 2 O z (Bi2212) found E g ∼ ∆, the superconducting gap energy. The results of ARPES experiments [14,15] also suggest that the PG has conventional d-wave symmetry while Raman results [3,5] indicate that the gap is more localized to regions of the Fermi surface (FS) located near the axes in reciprocal space.…”

Phonon Self-Energy in the Presence of Charge and Spin-Density Waves

“…Moreover, results discussed in Ref. [9] suggest that the pseudogap evolves smoothly into the superconducting gap. These features speak in favor of the hypothesis, that the pseudogap can act as a precursor of the superconducting gap [10].…”