Effect of Order Parameter Collective Mode on Electronic Raman Spectra of Spin-Triplet Superconductor Sr_2RuO_4(Condensed matter: electronic structure and electrical, magnetic, and optical properties)

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We discuss the electronic Raman spectra of the quasi-two-dimensional spin-triplet superconductor Sr_2RuO_4. The order parameter is assumed to have the orbital symmetry k_x ± ik_y and sin k_x ± i sin k_y. The Raman spectra are calculated using the Keldysh Green's function theory taking into account the order parameter collective mode. We also take into account the effect of impurity scattering. The order parameter collective modes in the two paring states give sizable contribution to the Raman spectra for the B_<1g> and B_<2g> modes. In the k_x ± ik_y state, since the energy gap is isotropic, the B_<1g> and B_<2g> spectra are the same. In the sin k_x ± i sin k_y state, the anisotropy of the gap yields significant mode dependence in the Raman spectra. The impurity scattering gives rise to considerable modification of the contribution from the quasiparticle excitations to the Raman spectra and simultaneously to the broadening of the collectivemode resonance peak and the shift of the peak position.
2007-03-15