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.

The electrical transport in the half-Heusler phases LuNiSb and YPdSb was measured in a temperature range 2–300 K. For both compounds, the electrical resistivity was found to decrease with increasing temperature, showing a linear-in-$T$ behavior over an extended temperature interval. In order to interpret the experimental data, a two-channel conductivity model was applied, which revealed that not only the semiconducting-like transport but also the metallic-like one exhibit negative temperature coefficients. The unusual behavior in the metallic channel was described within the Cote-Meisel formalism based on the diffraction model of strongly disordered metals. In addition, a weak localization scenario was considered including spin-orbit scattering and Coulomb interaction between conducting electrons. The electron-electron interaction was found most important at the lowest temperatures, where the semiconducting channel becomes ineffective, reminiscent of charge transport confined to a narrow yet finite-size metallic band located inside the semiconducting energy gap. The low-temperature resistivity of YPdSb appeared fully describable in terms of the Altshuler-Aronov quantum correction due to interacting electrons. In turn, the electronic transport in LuNiSb was found affected by the Kondo effect associated with a small amount of paramagnetic impurities present in the specimen investigated. The approach developed for LuNiSb and YPdSb can be applied to other half-Heusler compounds that exhibit atom disorder in their crystal structures.

Single crystals of the ternary cerium arsenide CeAgAs₂ were grown by chemical vapor transport. They were studied by means of x-ray diffraction, magnetization, heat capacity and electrical transport measurements. The experimental research was supplemented with electronic band structure calculations. The compound was confirmed to order antiferromagnetically at the Néel temperature of 4.9 K and to undergo metamagnetic transition in a field of 0.5 T at 1.72 K. The electrical resistivity shows distinct increase at low temperatures, which origin is discussed in terms of pseudo-gap formation in the density of states at the Fermi level and quantum corrections to the resistivity in the presence of atom disorder due to crystal structure imperfections.

We systematically investigate three body-centred cubic (bcc) high-entropy alloys (HEAs) with an identical valence electron count (VEC = 4.375): ( NbHf ) 0.75 ( TiZr ) 0.25 , ( NbZr ) 0.75 ( TiHf ) 0.25 , and ( NbTi ) 0.75 ( ZrHf ) 0.25 . Despite their isoelectronic nature, it was found that these alloys exhibit markedly different superconducting properties. Critical temperatures T c range from 7.14(5) K to 8.17(5) K, while upper critical fields μ 0 H c 2 ( 0 ) exceed 12 T, reaching 14.0(9) T for the Ti-rich alloy ( NbTi ) 0.75 ( ZrHf ) 0.25 . These variations highlight the limited predictive power of the Matthias rule in HEA design. Furthermore, the exceptional properties observed in the Ti-rich composition suggest that Nb and Ti are critical elements for the development of new HEAs for next-generation superconducting magnets.

Hybridization between $f$ electrons and conduction bands (c-f hybridization) is a driving force for many unusual phenomena. To provide insight into it, systematic studies of ${\mathrm{CeCoIn}}_5$ heavy fermion superconductor have been performed by angle-resolved photoemission spectroscopy (ARPES) in a large angular range at temperature of $T=6$ K. The used photon energy of 122 eV corresponds to Ce $4d\text{−}4f$ resonance. Calculations carried out with the relativistic multiple scattering Korringa-Kohn-Rostoker method and one-step model of photoemission yielded realistic simulation of the ARPES spectra, indicating that Ce-In surface termination prevails. Surface states, which have been identified in the calculations, contribute significantly to the spectra. Effects of the hybridization strongly depend on wave vector. They include a dispersion of heavy electrons and bands gaining $f$-electron character when approaching Fermi energy. We have also observed a considerable variation of $f$-electron spectral weight at $E_F$, which is normally determined by both matrix element effects and wave vector dependent c-f hybridization. Fermi surface scans covering a few Brillouin zones revealed large matrix element effects. A symmetrization of experimental Fermi surface, which reduces matrix element contribution, yielded a specific variation of $4f$-electron enhanced spectral intensity at $E_F$ around $\overline{\mathrm{\Gamma }}$ and $\overline{\mathrm{M}}$ points. Tight-binding approximation calculations for Ce-In plane provided the same universal distribution of $4f$-electron density for a range of values of the parameters used in the model.