We present the results of our comprehensive investigation on the antiferromagnetic heavy-fermion superconductor Ce3PtIn11 carried out by means of electrical transport, heat capacity and ac magnetic susceptibility measurements, performed on single-crystalline specimens down to 50 mK in external magnetic fields up to 9 T. Our experimental results elucidate a complex magnetic field – temperature phase diagram which contains both first- and second-order field-induced magnetic transitions and highlights the emergence of field stabilized phases. Remarkably, a prominent metamagnetic transition was found to occur at low temperatures and strong magnetic fields. In turn, the results obtained in the superconducting phase of Ce3PtIn11 corroborate an unconventional nature of Cooper pairs formed by heavy quasiparticles. The compound is an almost unique example of a heavy fermion system in which superconductivity may coexist microscopically with magnetically ordered state.

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We address the origin of the magnetic-field independent −|A| T 1/2 term observed in the lowtemperature resistivity of several As-based metallic systems of the PbFCl structure type. For the layered compound ZrAs1.58Se0.39, we show that vacancies in the square nets of As give rise to the low-temperature transport anomaly over a wide temperature regime of almost two decades in temperature. This low-temperature behavior is in line with the non-magnetic version of the twochannel Kondo effect, whose origin we ascribe to a dynamic Jahn-Teller effect operating at the vacancy-carrying As layer with a C4 symmetry. The pair-breaking nature of the dynamical defects in the square nets of As explains the low superconducting transition temperature Tc ≈ 0.14 K of ZrAs1.58Se0.39, as compared to the free-of-vacancies homologue ZrP1.54S0.46 (Tc ≈ 3.7 K). Our findings should be relevant to a wide class of metals with disordered pnictogen layers.

Single crystals of HfAs(1.7)Se(0.2) are grown by chemical transport reaction and their chemical composition characterized in detail by various analytical methods. Chemical analyses and crystal structure investigations by single-crystal X-ray diffraction as well as powder diffraction with synchrotron radiation reveal a tetragonal PbFCl structure type with strong disorder caused by a significant arsenic deficiency (As(0.9)) on the 2a site and mixed occupancy of the 2c site (As(0.8)Se(0.2)). HfAs(1.7)Se(0.2) is a diamagnetic metal which transforms into a superconducting state at T(c)=0.52 K. Similar to other PbFCl-type arsenide selenides, the title compound displays a magnetic-field-independent -AT(1/2) term in the low-temperature electrical resistivity. This unusual term presumably originates from the electron scattering of structural two-level systems. According to the experimental results, HfAs1.7Se0.2 appears to be a rare example of a nonmagnetic Kondo material.

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Magnetization, electrical-resistivity, specific-heat, and thermopower measurements were performed on single crystals of the filled skutterudite compound PrRu 4 As 12 . These measurements reveal a superconducting transition near 2.5 K that is quantified by: ͑1͒ magnetic susceptibility data which display an onset to a Meissner state at T c Ϸ 2.5 K and complete diamagnetic shielding as T → 2.0 K, ͑2͒ electrical-resistivity data which show a transition to a zero-resistance state at T c Ϸ 2.5 K, and ͑3͒ specific-heat and thermopower data which display "jumps" at T c Ϸ 2.5 K. Furthermore, the electronic contribution to the specific heat follows the BCS prediction for a superconductor. For temperatures above T c , magnetization measurements indicate local moment behavior where ef f = 3.52 B / Pr 3+ ion. Analysis of the data for T Ͼ T c , using a crystalline electric field model, suggests that PrRu 4 As 12 has a ⌫ 1 ground state with a ⌫ 4 first excited state at T ⌫ 4 Ϸ 95 K.

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