The noncentrosymmetric ferromagnetic Weyl semimetal CeAlSi with simultaneous space-inversion and time-reversal symmetry breaking provides a unique platform for exploring novel topological states. Here, by employing multiple experimental techniques, we demonstrate that ferromagnetism and pressure can serve as efficient parameters to tune the positions of Weyl nodes in CeAlSi. At ambient pressure, a magnetism-facilitated anomalous Hall/Nernst effect (AHE/ANE) is uncovered. Angle-resolved photoemission spectroscopy (ARPES) measurements demonstrated that the Weyl nodes with opposite chirality are moving away from each other upon entering the ferromagnetic phase. Under pressure, by tracing the pressure evolution of AHE and band structure, we demonstrate that pressure could also serve as a pivotal knob to tune the positions of Weyl nodes. Moreover, multiple pressure-induced phase transitions are also revealed. These findings indicate that CeAlSi provides a unique and tunable platform for exploring exotic topological physics and electron correlations, as well as catering to potential applications, such as spintronics.

The binary phase SrSi₆ was prepared at a pressure of 10(1) GPa and a temperature of 1520(150) K. Single crystal refinements and powder diffraction data reveal that the compound crystallizes in the orthorhombic crystal system (Cmcm, a=4.4692(4), b=10.256(1), c=11.698(1)Å ) and is isopointal to EuGa₂Ge₄ and EuSi₆. Exothermic decomposition of the compound into SrSi₂ and Si at 797 K and ambient pressure indicates that the compound is a metastable high-pressure phase. Analysis of the chemical bonding using the electron localization function and calculated charge densities reveals covalent bonding within the polyanion of four-bonded silicon atoms. Strontium cations are enclosed in the 3D net resulting in an electron balance Sr²⁺[Si⁰]²⁻ ₆ . In the electronic density of states the excess electrons of the framework are assigned to a filling of antibonding bands. SrSi₆ is a metallic conductor with an electrical resistivity of ρ ≈ 250 μΩ·cm at 300 K. Magnetization measurements indicate diamagnetic behaviour (χ₀ = −50 · 10⁻⁶ emu·mol⁻¹).

The absence of centrosymmetry in chiral and polar crystal structures is the reason for many technical relevant physical properties like optical birefringence or ferroelectricity. Other chirality related properties that are actually intensively investigated are unconventional superconductivity or unusual magnetic ordering like skyrmions in materials with B20 structure. Despite the often close crystal structure - property relation, its detection is often challenging due to superposition of domains with different absolute structure e.g. chirality. Our investigations of high quality CoSi crystals with B20 structure by both complementary methods X- ray (volume sensitive) and electron backscatter diffraction (EBSD) (surface sensitive) results the consistent assignment of the chirality and reveal fundamental differences in their sensitivity to chirality. The analysis of the surface of a CoSi crystal with domains of different chirality show the high spatial resolution of this method which opens the possibility to analyze the chirality in microstructures of technical relevant materials like thin films and catalysts.

The assignment of enantiomorphs by diffraction methods shows fundamental differences for x-rays and electrons. This is particularly evident for the chiral allotrope of β-Mn. While it is not possible to determine the sense of chirality of β-Mn with established x-ray diffraction methods, Kikuchi pattern simulation of the enantiomorphs reveals differences, if dynamical electron diffraction is considered. Quantitative comparison between experimental and simulated Kikuchi patterns allows the spatially resolved assignment of the enantiomorph in polycrystalline materials of β-Mn, as well as the structurally strongly related phase Pt₂Cu₃B. On the basis of enantiomorph distribution maps, crystals were extracted from enantiopure domains by micropreparation techniques. The x-ray diffraction analyses confirm the assignment of the Kikuchi pattern evaluations for Pt₂Cu₃B and do not allow to distinguish between the enantiomorphs of β-Mn.

Single crystals of $\mathrm{Ce}{\mathrm{Pt}}_4\mathrm{In}$ were studied by means of magnetic susceptibility and Seebeck coefficient measurements. Moreover, $\mathrm{Ce}\text{−}{\mathrm{L}}_{\mathrm{III}}$ edge x-ray absorption near-edge structure experiments were performed on polycrystalline samples. The results show that the $4f$ electrons in this compound have fairly localized character, with rather stable $4f^1$ configuration. These findings supplement previous literature reports on $\mathrm{Ce}{\mathrm{Pt}}_4\mathrm{In}$ being a valence fluctuation system.

A valence instability of Eu in ${\text{EuPd}}_3{\text{B}}_x$ $\left(0\le x\le 1\right)$ was discussed controversially in the past. In a joint theoretical and experimental study we investigate a large series of ${\text{EuPd}}_3{\text{B}}_x$ and ${\text{GdPd}}_3{\text{B}}_x$ compounds. Characterization by x-ray diffraction, metallography, energy-, and wavelength-dispersive x-ray spectroscopy as well as chemical analysis determine an existence range of ${\text{EuPd}}_3{\text{B}}_x$ up to $x\le 0.53$ and $x\le 0.42$ for the ${\text{GdPd}}_3{\text{B}}_x$ compounds, respectively. Our density-functional-based electronic structure calculation predict a valence change in ${\text{EuPd}}_3{\text{B}}_x$ above $x_c^{\text{DFT}}=0.19\pm 0.02$ from a nonmagnetic ${\text{Eu}}^{3+}$ state into a magnetic ${\text{Eu}}^{2+}$ state which is reflected in a discontinuity of the lattice parameter. In contrast, the related Gd compounds with a stable ${\text{Gd}}^{3+}$ state exhibit an almost linear behavior of the lattice parameter following Vegard’s law. Consistent with the calculations, the x-ray diffraction data show a kink in the lattice parameter for ${\text{EuPd}}_3{\text{B}}_x$ at $x_c^{\text{XRD}}=0.22\pm 0.02$. X-ray absorption spectroscopy measurements assign this kink to a transition into a heterogeneous mixed valence state for Eu with a critical B content $x_c^{\text{XAS}}=0.22\pm 0.03$. The observed change in the mean Eu valence from ${\text{Eu}}^{3+}$ $\left(x\le 0.2\right)$ toward ${\text{Eu}}^{2.5+}$ $\left(x=0.5\right)$ is supported by magnetic susceptibility and specific-heat data.