Superconductivity-induced resonant Raman scattering in multilayer high-Tcsuperconductors

Abstract

Resonant Raman scattering below T c has been discovered in several Bi-, Hg-, Tl-based high-Tc superconductors with three or four CuO2-layers. For Bi 2 Si 2 Ca 2 Cu 3 O 10+ δ , we found an unexpected crossover of the pair-breaking peak in the A 1g -spectrum from a broad bump at hω = 6k B T c for E exc = 2.54eV to a sharp peak at hω = 8kBTc for Eexc = 2.18eV, together with a strong enhancement of the Ca-phonons. Under resonant conditions, the relative positions of the pair breaking peaks in A 1g , B 1g , and B 2g channels are 2∆(A 1g ) = 2∆(B 1g ) > 2∆ (B 2g ). This relation implies that the A 1g Raman channel is free from the Coulomb screening effect, just as predicted theoretically for a d-wave multi-layer superconductor but have never been observed experimentally thus far. The observed resonance effect is the evidence that the electronic state in the inner CuO 2 -planes is different from that of the outer CuO 2 -planes.

Superconducting gap of overdoped Tl2Ba2CuO6+δ observed by Raman scattering

“…In the optimally doped regime, as it has d wave symmetry, the (B 1g ). Actually in the three layer compounds such as Bi 2223, this behavior is observed due to the loss of screening effects [14]. However, since the A 1g peak intensity is strongly suppressed in the heavily overdoped case, we conclude that the screening effect does exist in the present crystals.…”

Electronic and phononic Raman scattering in detwinnedYBa2Cu3O6.95andBakr1, Schnyder2, Klam3 et al. 2009Phys. Rev. B343340View full textAdd to dashboardCite

“…55͒ and Bi 2 Sr 2 CaCu 2 O 8 . 59,60 Within the error bars of ϳ0.8 cm −1 in ͑a͒-͑c͒ and 2.0 cm −1 in ͑d͒, the phonon peak position and linewidth of the 340 cm −1 mode is the same for the xx and yy polarizations ͑see Fig. 7͒.…”

c-axis lattice dynamics in Bi-based cuprate superconductors

“…Our data clearly demonstrate the superconductivity-induced enhancement of the phonon bands at 260 and 390 cm −1 and a broad band peaking around 550 cm −1 . There are two alternative explanations of these superconductivity-induced anomalies in multilayer high-T c compounds; one considers the broad excitation band as a "pair-breaking" peak at 2∆ [52], and the another refer it to a Raman-active c axis plasmon [53]. A more detailed study of the doping effect on the resonance peak position is required to clarify its origin.…”