[en] The competition between the Kondo effect and the Ruderman-Kittel-Kasuya-Yosida exchange interaction determines the ground state of most heavy-fermion compounds. By employing non-thermal tuning parameters like pressure and magnetic field, Fermi liquids and magnetically ordered phases can be tuned smoothly to each other in these compounds, offering an ideal playground for quantum criticality. On the other hand, spin frustration is an effective approach to produce novel quantum phenomena such as spin liquids in insulating quantum magnets. Introducing spin frustration into heavy fermion systems will profoundly affect their ground state, and is emerging as a new research direction. Following a brief introduction to frustrated heavy-fermion compounds, we will first describe our recent work on frustrated CePdAl, and then discuss the observed quantumcritical phase that is intimately related to spin frustration. (authors)

[en] Needle-like single crystals of CeAu₂In₄ have been grown from In flux and characterized as a new candidate of quasi-one-dimensional Kondo lattice compound by crystallographic, magnetic, transport, and specific-heat measurements down to very low temperatures. We observe an antiferromagnetic transition at T _N ≈ 0.9 K, a highly non-mean-field profile of the corresponding peak in specific heat, and a large Sommerfeld coefficient γ = 369 mJ⋅mol⁻¹⋅K⁻². The Kondo temperature T _K is estimated to be 1.1 K, being low and comparable to T _N. While Fermi liquid behavior is observed deep into the magnetically ordered phase, the Kadowaki–Woods ratio is much reduced relative to the expected value for Ce compounds with Kramers doublet ground state. Markedly, this feature shares striking similarities to that of the prototypical quasi-one-dimensional compounds YbNi₄P₂ and CeRh₆Ge₄ with tunable ferromagnetic quantum critical point. Given the shortest Ce–Ce distance along the needle direction, CeAu₂In₄ appears to be an interesting model system for exploring antiferromagnetic quantum critical behaviors in a quasi-one-dimensional Kondo lattice with enhanced quantum fluctuations. (rapid communication)

[en] Kondo semimetal CeRu₄Sn₆ is attracting renewed attention due to the theoretically predicted nontrivial topology in its electronic band structure. We report hydrostatic and chemical pressure effects on the transport properties of single- and poly-crystalline samples. The electrical resistivity ρ(T) is gradually enhanced by applying pressure over a wide temperature range from room temperature down to 25 mK. Two thermal activation gaps estimated from high- and low-temperature windows are found to increase with pressure. A flat ρ(T) observed at the lowest temperatures below 300 mK appears to be robust against both pressure and field. This feature as well as the increase of the energy gaps calls for more intensive investigations with respect to electron correlations and band topology. (paper)

[en] We report on anisotropic electrical, thermal as well as thermoelectric properties of the prototypical Weyl semimetal TaAs. Compared to the normal metallic behavior along a axis, TaAs is more electrically resistive along c axis and exhibits a semiconductor-like resistivity upturn below $T\approx <!--\; ???\; -->25$ K. In the same temperature range, the thermal conductivity along c axis shows a pronounced maximum of 183 ${\mathrm{W}\mathrm{K}\mathrm{m}}^{-<!--\; ???\; -->1}$ characteristic of a crystalline solid, three times higher than that of a axis. The thermoelectric power, while exhibiting enhanced values around room temperature, becomes diminished in a substantial range of temperature ($T<50$ K) for both axes. Together with the enhanced Nernst signals, this hints at a dominating ambipolar diffusion as is frequently seen in a compensated semimetal. An in-depth investigation of the anisotropic transport quantities is expected to yield deep insights into the propagating Weyl fermions in TaAs. (paper)