Superconducting Properties of Pr-Based Filled Skutterudite PrRu₄As₁₂

Abstract

We report on a systematic study of the superconducting characteristics and Pr crystallineelectric-field (CEF) levels of the filled skutterudite PrRu4As12 (Tc = 2.33 K). The temperature dependences of the upper critical field Hc2 and the Ginzburg-Landau (Maki) parameter κ2 suggest s-wave clean-limit superconductivity. The electronic specific heat coefficient γ ∼ 95 mJ/K 2 mol, which is ∼ 1.5 times larger than that of LaRu4As12, indicates 4f -originating quasiparticle mass enhancement. The magnetic susceptibility χ(T ) indicates that the CEF ground state is a Γ1 singlet and a Γ (1) 4 triplet first excited state lies at ∆CEF ∼ 30 K above. A systematic comparison among PrOs4Sb12, PrRu4Sb12, PrRu4As12, and La-based reference compounds suggests that the inelastic exchange scattering and aspherical charge scattering of conduction electrons from CEF-split 4f levels play an essential role in the quasiparticle mass enhancement and in determining the value of Tc in the Pr-based filled skutterudites.

Crystal Growth and Properties of the Filled Skutterudite Arsenides

“…[3][4][5][6][7][8] The limited research in this direction may be due to materials difficulties related to the elevated vapor pressure of arsenic. In contrast, crystals of both the phosphides 9 and the antimonides 10 can be grown by low pressure flux techniques.…”

Superconducting Properties of LaRu4As12Synthesized at High Pressure

“…µ 0 H c2 (0) value is estimated to be ∼ 9.6 T by the WHH fitting. There appears a possibility of the slight upward deviation in the µ 0 H c2 curve below 2 T, leading to an enhancement in T c by ∼ 10 % in zero field compared with the best-fit WHH curve for µ 0 H c2 (T ) > 2 T. This behavior is also observed in PrRu 4 As 12 13 and PrOs 4 Sb 12 , 24 suggesting that the upward deviation in T c may come from the multiband effect. This multiband effect is also suggested by NQR measurement.…”

“…[8][9][10][11] On the other hand, PrRu 4 As 12 and PrRu 4 Sb 12 show BCS-type SC properties. 12,13 It is suggested that crystal electric field plays an important role to the heavy ferimon SC properties of PrOs 4 Sb 12 .…”

“…In addition, its substituted compound PrRu 4 As 12 is pointed out the possibility of the multiband SC of LaRu 4 As 12 . 13,19 It is also important to realize the origin of the multiband effect observed in PrRu 4 As 12 13 by studying the superconducting properties of the isostructural compound LaRu 4 As 12 . Systematic understanding for such variety in the SC properties of filled skutterudites is one of the important issues.…”

75As-NQR Studies of Filled-Skutterudites PrRu4As12and LaRu4As12

“…8 The X-ray analysis shows that the samples contain some impurity phase, which is mainly RuAs 2 . The samples are powdered for the NQR measurements.…”