Theoretical studies on the observation of the low-frequency plasma oscillation and its coupling with the Carlson-Goldman mode in dirty quasi-two-dimensional superconductors

Abstract

The plasma oscillation in a superconductor is investigated for the case when the plasma energy is smaller than the superconducting gap. We show that the plasma energy has a temperature dependence in dirty superconductors. When the strength of the impurity scattering exceeds a critical value, the plasma disappears at the transition temperature TC as observed in high-TC cuprates (Bi2Sr2CaCu2O8+δ). We also study the coupling of the plasma with the Carlson-Goldman (CG) mode in a dirty superconductor. A pole analysis show that the coupling occurs just below TC. However, even in this situation, we find that two different modelike peak structures can be still observed in the spectra of the density-density correlation function [Π33(q,ω)] and the structure function of the pair field susceptibility [S(q,ω)]: The peak in Π33 is located at a finite energy at q∼0 corresponding to the low-frequency plasma, while the CG mode with a linear dispersion is found in S(q,ω).

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