Collective phase oscillation in two-dimensional d-wave superconductors

Y. Ohashi; S. Takada

doi:10.1103/PhysRevB.62.5971

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Collective phase oscillation in two-dimensional d-wave superconductors

Y. Ohashi, S. Takada

DOI 10.1103/PhysRevB.62.5971 · Physical Review B

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Abstract

We theoretically investigate the Carlson-Goldman (CG) mode in two-dimensional dx2−y2-wave superconductivity. In conventional s-wave superconductors, it is known that the CG mode is observed as a peak in the structure function of the pair field susceptibility S(q,ω) only just below the transition temperature Tc and only in dirty systems. On the other hand, in the d-wave state, we show that the peak structure can be observed down to T≃0.2Tc in clean systems. Furthermore, we also show that the peak splits into two when the direction of the momentum q deviates from the qx or qy axes, or nodal directions of the order parameter. These features originate from a singularity in the charge-density fluctuation due to the presence of the nodes of the d-wave order parameter: It enhances the screening of the long-range Coulomb interaction so that the CG mode can exist far below Tc. We also investigate a quasi-two-dimensional system, and show that the Josephson plasma can be observed in S(q,ω) when q is parallel to the c direction.