Evolution of specific heat with controlled disorder in filled skutterudite superconductor LaRu₄As₁₂

In filled skutterudite compounds, the lanthanoid atoms are surrounded by cages of pnictogen atoms, often exhibiting characteristic motion in the anharmonic potential known as rattling. It is proposed that the rattling motion is related to the exotic heavy-fermion state or unconventional superconductivity in some filled skutterudite compounds containing 4f electrons[1,2]. However, it remains unclear how the rattling motion affects the normal-state and superconducting properties when the system does not possess 4f electrons. The filled skutterudite LaRu₄As₁₂ shows multigap superconductivity at T_c = 10.5 K and has relatively large Sommerfeld coefficient γ ~ 60 mJ/molK² in spite of the absence of 4f electrons. Here, we introduce defects of the guest atoms and cage atoms in LaRu₄As₁₂ single crystals using electron irradiation which allows us to investigate the impact of atomic defects in a controllable manner. We report on the evolution of specific heat with increasing atomic defects and discuss the superconducting gap structure and normal-state electronic properties.
[1]T.Hotta, J. Phys. Soc. Jpn. 77, 103711 (2008).
[2]T.Goto et al., Phys. Rev. B 69, 180511(R) (2004).