Condensate pair fluctuations in a two-dimensional d-wave superconductor and Raman scattering

Wen-Chin Wu, A. Griffin

Research output: Contribution to journalArticle

16 Citations (Scopus)

Abstract

The condensate pair fluctuations in the frequency region ω 2Δ and the associated Raman-scattering intensity of a two-dimensional (2D) d-wave weak-coupling BCS superconductor are investigated. Our model includes a dominant dx2-y2 (L=2) and a weaker s-wave (L=0) pairing interaction. All response functions involving density and pair operators are evaluated (in the low-q limit). For neutral d-wave superconductors (no Coulomb interaction), the expected phononlike phase mode is obtained in the L=0 channel (which couples to density fluctuations). In contrast, excitonlike modes corresponding to excited Cooper pair states are obtained in the L=2 channel. We find an amplitude fluctuation mode with frequency 3 Δ. For charged d-wave superconductors, the L=0 phonon is renormalized into a 2D plasmon, but the L=2 excitonlike mode remains unaffected by the Coulomb interaction. At T=0, the latter is shown to be completely washed out in the Raman scattering spectrum (q=0) due to large p-h damping (which arises in the absence of a finite pair-breaking gap in d-wave superconductors). However, at finite temperatures, we find the energy of the excitonlike mode is drastically lowered [relative to 2Δ(T)] when the s-wave attraction is comparable to the d-wave pairing. This leads to a decrease in the damping and, as a result, the mode shows up as a low-frequency resonance in the Raman cross section. Due to the anisotropy of the d-wave order parameter, the quasiparticle excitation spectrum and the noninteracting two-particle spectrum are strongly dependent on the direction of q. We also find that the excitonlike mode frequency becomes anisotropic for wave vectors of the order of Δ/vF.

Original languageEnglish
Pages (from-to)1190-1205
Number of pages16
JournalPhysical Review B
Volume51
Issue number2
DOIs
Publication statusPublished - 1995 Jan 1

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Superconducting materials
condensates
Raman scattering
Raman spectra
scattering
Coulomb interactions
Damping
damping
interactions
Probability density function
attraction
Mathematical operators
Anisotropy
low frequencies
operators
anisotropy
cross sections
excitation

ASJC Scopus subject areas

  • Condensed Matter Physics

Cite this

Condensate pair fluctuations in a two-dimensional d-wave superconductor and Raman scattering. / Wu, Wen-Chin; Griffin, A.

In: Physical Review B, Vol. 51, No. 2, 01.01.1995, p. 1190-1205.

Research output: Contribution to journalArticle

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