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Boron-rich materials combine chemical stability with refractory properties and, consequently, are interesting for high-temperature thermoelectric applications. Therefore, the magnetic, electrical, and thermal transport properties of the ${\mathrm{Y}}_{1\ensuremath{-}x}{\mathrm{Ce}}_{x}{\mathrm{CrB}}_{4}$ series have been investigated here to employ the concept of correlation-enhanced thermoelectric properties. Combining x-ray diffraction and energy- or wavelength-dispersive spectrometry, we find a rather narrow stability range of ${\mathrm{Y}}_{1\ensuremath{-}x}{\mathrm{Ce}}_{x}{\mathrm{CrB}}_{4}$, only samples on the Y- and Ce-rich substitution limits $(x=0,\phantom{\rule{0.28em}{0ex}}0.05,\phantom{\rule{0.28em}{0ex}}0.95,\phantom{\rule{0.28em}{0ex}}\mathrm{and}\phantom{\rule{0.28em}{0ex}}1)$ were obtained. Electrical resistivity data show a change from semiconducting $(x=0)$ to metallic behavior upon Ce substitution $(x\ensuremath{\ge}0.95)$. From magnetic susceptibility measurements and x-ray absorption spectroscopy, we find a temperature-dependent intermediate valence state of Ce of about $+3.5$. However, a fit of the magnetic susceptibility data to the Coqblin-Schrieffer model yields a surprisingly high Kondo temperature of about 1100 K. Together with the good thermal conductivity for the studied substitution series this impedes a suitable thermoelectric performance. Electronic structure calculations for ${\mathrm{YCrB}}_{4}$ support its narrow gap semiconducting nature in contrast to previous studies. Surprisingly, its electronic structure is characterized by pronounced van Hove singularities very close to the Fermi-level ${E}_{\mathrm{F}}$. They originate from nearly dispersionless Cr $3{d}_{{z}^{2}\ensuremath{-}{r}^{2}}$-derived bands in a large part of the Brillouin zone, suggesting the appearance of electronic instabilities upon rather small electron doping into these states.

${\mathrm{TaSnS}}_{2}$ single crystal and polycrystalline samples are investigated in detail by magnetization, electrical resistivity, and specific heat as well as Raman spectroscopy and nuclear magnetic resonance (NMR). Studies are focused on the temperature and magnetic field dependence of the superconducting state. We determine the critical fields for both directions $B\ensuremath{\parallel}c$ and $B\ensuremath{\perp}\phantom{\rule{0.16em}{0ex}}c$. Additionally, we investigate the dependence of the resistivity, the critical temperature, and the structure through Raman spectroscopy under high pressure up to 10 GPa. At a pressure of $\ensuremath{\approx}3\phantom{\rule{0.28em}{0ex}}\mathrm{GPa}$ the superconductivity is suppressed below our minimum temperature. The Sn NMR powder spectrum shows a single line which is expected for the ${\mathrm{TaSnS}}_{2}$ phase and confirms the high sample quality. Pronounced de Haas-van Alphen oscillations in the ac susceptibility of polycrystalline sample reveal two pairs of frequencies indicating coexisting small and large Fermi surfaces. The effective mass of the smaller Fermi surface is $\ensuremath{\approx}0.5{m}_{\mathrm{e}}$. We compare these results with the band structures from DFT calculations. Our findings on ${\mathrm{TaSnS}}_{2}$ are discussed in terms of a quasi-two-dimensional BCS superconductivity.

${\mathrm{LaPtGe}}_{3}$ and ${\mathrm{CePtGe}}_{3}$ crystallize with a noncentrosymmetric body-centered tetragonal (space group $I4mm$)$\phantom{\rule{4pt}{0ex}}{\mathrm{BaNiSn}}_{3}$-type of structure. ${\mathrm{LaPtGe}}_{3}$ is a weakly coupled BCS-like $s$-wave type-I superconductor with ${T}_{\mathrm{c}}=0.55$ K, ${B}_{\mathrm{c}}\ensuremath{\simeq}14$ mT, and Ginzburg-Landau parameter ${\ensuremath{\kappa}}_{\mathrm{GL}}=0.021l1/\sqrt{2}$. ${\mathrm{CePtGe}}_{3}$ is a nonsuperconducting (${T}_{\mathrm{nsc}}=0.35$ K) metal with an effective magnetic moment ${\ensuremath{\mu}}_{\mathrm{eff}}=2.46{\ensuremath{\mu}}_{\mathrm{B}}$. The Ce moments show two antiferromagnetic ordering transitions at ${T}_{\mathrm{N}1}\ensuremath{\approx}3.7$ K and ${T}_{\mathrm{N}2}\ensuremath{\approx}2.7$ K and a ground-state multiplet $J=5/2$ splitting into three doublets (energy splittings from the ground state ${\mathrm{\ensuremath{\Delta}}}_{1}=46$ K and ${\mathrm{\ensuremath{\Delta}}}_{2}=137$ K). The moderately enhanced Sommerfeld coefficient ${\ensuremath{\gamma}}_{0}$ and the observation of almost the full critical magnetic entropy at ${T}_{\mathrm{N}1}$ suggest that magnetic Ruderman-Kittel-Kasuya-Yosida-type interactions are dominant in ${\mathrm{CePtGe}}_{3}$, leading to a magnetically ordered ground state.

Mixed spin-singlet and spin-triplet pairing can occur in noncentrosymmetric superconductors. In this respect, a comprehensive characterization of the noncentrosymmetric superconductor BeAu was carried out. It was established that BeAu undergoes a structural phase transition from a low-temperature noncentrosymmetric FeSi structure type to a high-temperature centrosymmetric structure in the CsCl type at ${T}_{\text{s}}=860$ K. The low-temperature modification exhibits a superconducting transition below ${T}_{\text{c}}=3.3$ K. The values of lower (${H}_{\text{c1}}=32$ Oe) and upper (${H}_{\text{c2}}=335$ Oe) critical fields are rather small, confirming that this type-II (${\ensuremath{\kappa}}_{\text{G-L}}=2.3$) weakly coupled (${\ensuremath{\lambda}}_{\text{e-p}}=0.5,\phantom{\rule{0.28em}{0ex}}\mathrm{\ensuremath{\Delta}}{C}_{\text{e}}/{\ensuremath{\gamma}}_{\text{n}}{T}_{\text{c}}\ensuremath{\approx}1.26$) superconductor can be well understood within the Bardeen-Cooper-Schrieffer theory. The muon spin relaxation analysis indicates that the time-reversal symmetry is preserved when the superconducting state is entered, supporting conventional superconductivity in BeAu. From the density functional band structure calculations, a considerable contribution of the Be electrons to the superconducting state was established. On average, a rather small mass renormalization was found, consistent with the experimental data.

Unusual physical properties like large magnetoresistance (MR) and superconductivity occurring in semimetals with Dirac or Weyl points are often linked to their topologically nontrivial band structures. However, there is an increasing number of reports on semimetals that show large MR in the absence of Dirac or Weyl points. Herein we report an experimental and theoretical study on the layered transition-metal dichalcogenide (TMDC) $\mathrm{HfT}{\mathrm{e}}_{2}$ that shows a large MR of $1350%$ at $T=2$ K and ${\ensuremath{\mu}}_{0}H=9\phantom{\rule{0.16em}{0ex}}\mathrm{T}$ in the absence of Dirac or Weyl points. Moreover, the structure and electrical resistivity under pressure reveal a unique structural transition. These results clearly distinguish $\mathrm{HfT}{\mathrm{e}}_{2}$ from TMDCs like $\mathrm{MoT}{\mathrm{e}}_{2}$ or $\mathrm{WT}{\mathrm{e}}_{2}$ which both exhibit larger MR and are viewed as Weyl semimetals. $\mathrm{HfT}{\mathrm{e}}_{2}$ is an appealing platform for future investigations on the interplay of particular band-structure features and their connection to emerging physical properties.

The crystallographic structures of decagonal quasicrystals and their periodic approximants are traditionally described as a periodic stacking of atomic planes. By performing a A 27 l NMR spectroscopic study of the Al13 M4 (M=transition metal) family of four-layer decagonal approximants, including the orthorhombic o-Al13 Co4, the monoclinic Al13 Fe4, its ternary derivative Al13 (Fe,Ni) 4, and the monoclinic Al13 Ru4, we show that all these phases contain structural detail of a nearly linear M-Al-M atomic group trapped inside an elongated cage, resembling the three-dimensional (3D) \"cage-compound\" structure of the intermetallic clathrates. We determined the electric-field-gradient- (EFG) and the magnetic-shielding tensors at the Al site of the M-Al-M groups. The asymmetry parameter of the EFG tensor was estimated theoretically by a point-charge model, taking into account the charges of both the M-Al-M atoms and the surrounding cage atoms. The calculations support ionic bonding of the M-Al-M group to the cage atoms and the existence of a 3D chemical bonding network in the Al13 M4 phases. The above results show that the traditional description of the Al13 M4 decagonal approximant phases in terms of two-dimensional (2D) atomic layers stacked along the pseudotenfold crystallographic direction is a convenient geometrical approach to describe their complex structures but is not appropriate for the description of their physical properties, which should be analyzed by taking into account the full 3D nature of the chemical bonding framework. This favors the 3D cage-compound structural description of the Al13 M4 phases over the pseudo-2D stacked-layer description.

We present a detailed study of $^{75}\text{A}\text{s}$ nuclear magnetic resonance Knight shift and spin-lattice relaxation rate in the normal state of stoichiometric polycrystalline LiFeAs. Our analysis of the Korringa relation suggests that LiFeAs exhibits strong antiferromagnetic fluctuations, if transferred hyperfine coupling is a dominant interaction between $^{75}\text{A}\text{s}$ nuclei and Fe electronic spins, whereas for an on-site hyperfine coupling scenario, these are weaker, but still present to account for our experimental observations. Density-functional calculations of electric field gradient correctly reproduce the experimental values for both $^{75}\text{A}\text{s}$ and $^{7}\text{L}\text{i}$ sites.