Low temperature specific heat of La₃Pd₄Ge₄ with U₃Ni₄Si₄-type structure

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Low temperature specific heat has been investigated in a novel ternary superconductor La₃Pd₄Ge₄ with an U₃Ni₄Si₄-type structure consisting of the alternating BaAl₄ (ThCr₂Si₂)- and AlB₂-type layers. A comparative study with the related ThCr₂Si₂-type superconductor LaPd₂Ge₂, one of the layers in La₃Pd₄Ge₄, is also presented. From the normal state specific heat, the Sommerfeld coefficient γₙ = 27.0 mJ/mol K² and the Debye temperature Θ D = 256 K are derived for the La₃Pd₄Ge₄, while those for the LaPd₂Ge₂ are γₙ =8.26 mJ/mol K² and Θ D = 291 K. The La₃Pd₄Ge₄ has moderately high electronic density of state at the Fermi level. Electronic contribution on the specific heat, C el, in each compound is well described by the BCS behavior, suggesting that both of the La₃Pd₄Ge₄ and the LaPd₂Ge₂ have fully opened isotropic gap in the superconducting state.