Comparative photoemission studies on the superconducting gap of the filled skutterudite superconductors LaPt ₄Ge ₁₂ and PrPt ₄Ge ₁₂

We performed a comparative study of the superconducting gap in the new filled skutterudite superconductors LaPt ₄Ge ₁₂ and PrPt ₄Ge ₁₂ using high-resolution photoemission spectroscopy. We succeeded in observing spectral changes across T _c that reflect the opening of the superconducting gap in both compounds and also in observing a noticeable difference in their respective superconducting spectral shapes near the Fermi level, pointing toward a more complex superconducting gap structure in PrPt ₄Ge ₁₂. In addition, we found that the two-gap model is more suitable for describing the superconducting-state spectrum of PrPt ₄Ge ₁₂ than the single-isotropic-gap and single-anisotropic-gap models, which suggests an explanation that multiband effects may possibly induce the anomalous superconducting properties of PrPt ₄Ge ₁₂.