Temperature dependence of c-axis Josephson plasma oscillation in high superconductors

We present a microscopic theory for the c-axis transverse Josephson plasma oscillation in quasi-two-dimensional d-wave superconductors. In our model, the incoherent motion of electrons along the c axis are introduced by potential scattering with arbitrary scattering strength, and their depairing effect on superconductivity is determined self-consistently. We show that the plasma frequency decreases with increasing temperature in the presence of the scattering. In particular, when the scattering strength exceeds a critical value, it vanishes at the transition temperature (Formula presented) as is observed in (Formula presented) In this case, when the scattering is in the Born limit, the V-shaped superconducting density of states (DOS) can be obtained in spite of the impure system. This result can explain why the V-shaped DOS is observed in this material by tunneling experiment although the temperature-dependent plasma indicates the presence of a scattering. Our model also produces a good fit to experimental data on (Formula presented) From the fit, we find that both the superfluid and the normal electrons contribute to the plasma oscillation in this material. This feature is different from the ordinary Josephson plasma, which is the oscillation of only the superfluid component.