Light-scattering study of the superconducting energy gap in YBa2Cu3

Abstract

Raman scattering experiments have been performed on single-crystal samples of YBa2Cu307 in order to investigate superconducting gap excitations. The electronic contribution to the total scattering intensity can be fitted well by a theoretical model of light scattering from quasiparticle pairs. Depending on the measuring symmetry, mean gap energies are found ranging from 3.0 to 5.5 kgTc The discovery of the new high-T, superconductors' has initiated unprecedented experimental and theoretical efforts in trying to understand the coupling mechanism. ' While pair correlations of charge carriers seems to follow from the observed quantum of flux (@n h/2e) and from Andreev scattering, experiments on the determination of the energy gap, 2h, still disagree widely. 6 may show considerable anisotropy, as was suggested from the beginning by both the structural and the superconducting properties of YBa2Cu307. A recent tunneling study on single crystals reported gap values of 3.6 and 5.9 ktt T, for wave vectors parallel and perpendicular to the CuO a bplanes-, respectively. As was shown first b Dierker, Klein, Webb, and Fisk in the 815 compounds, Raman scattering may

Study of the superconducting gap inRNi2B2C(R=Yang1, Klein2, Cooper3 et al. 2000Phys. Rev. B514330View full textAdd to dashboardCite

“…15 The lack of the complete suppression of the Raman response below the 2∆ peak has been regarded as evidence that the superconducting gap function of cuprates has nodes where the gap vanishes. 22 In simple BCS picture no density of states is allowed below the superconducting gap; thus, no Raman scattering beyond small smearing effects is expected below the gap in BCS-type superconductors.…”

“…13 Raman spectroscopy studies have played an important role in understanding superconductivity of conventional 14 and exotic superconductors. 15 For example, superconductivity-induced redistribution of the electronic continua of the high-T c superconductors led to important clues as to the d-wave nature of the order parameter. However, there remain unsolved puzzles regarding different values of the 2∆ peak positions in different scattering geometries, the power-law behavior of the scattering response below 2∆ and its relation to the d-wave nature of the order parameter, and to the role of impurities.…”

Electronic Raman scattering in the single-CuO2layered superconductorTl2Gasparov1, Lemmens2, Brinkmann3 et al. 1997Phys. Rev. B301182View full textAdd to dashboardCite

“…In high temperature superconductors, the first measurements of electronic Raman scattering were reported in Refs. [16][17][18][19]. But in this case the behavior of the electronic scattering differs from that in conventional superconductors: A pair breaking peak develops in the spectra below T c , but the scattering intensity at frequencies below 2∆ does not show the usual sharp decrease.…”

“…Instead, a monotonic decrease toward zero frequency is found. Moreover, for different symmetry components (A 1g , B 1g and B 2g ) the renormalization of the scattering intensity for T<T c is different and they exhibit peaks at different frequencies [18][19][20][21][22][23][24][25][26][27]29,30 . These facts have been explained by Devereaux et al 26,27 in terms of d x 2 −y 2 -wave pairing.…”

Resonant Raman scattering from superconducting single crystals of (BEDT-TTF)2I3

“…Raman scattering spectra of the HTSC above T~ consist of an almost constant background attributed to electron-ic excitations and superimposed structures due to scattering from phonons. In the superconducting state the electronic scattering strength decreases for low frequencies, overshoots the normal conducting one in the middle frequency region, and asymptotically approaches unity for high energy transfers [, [13][14][15][16].…”