Electrodynamics of the Superconducting State in CeRu2.

We have studied the complex conductivity in superconducting and normal metallic states of CeRu 2 by the surface impedance measurements at millimeter-wave frequency of 45.4 GHz. The temperature dependence of the complex conductivity below T c = 6.2 K exhibits the characteristic behaviors as seen in a conventional superconductor. The coherence peak observed in the real part σ 1 provides a strong evidence for a conventional s -wave superconductivity as well as the previous NQR measurements. The temperature dependence of the penetration depth evaluated from the surface reactance at low temperatures has revealed the ratio of 2 Δ(0)/ k B T c = 4.4. The strong-coupling theories suggest the electron-phonon coupling strength with λ ep < 2. These results indicate that CeRu 2 is an intermediate strong-coupling superconductor in a clean limit.

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