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Abstract Phases with spontaneous time-reversal ( $${{{{{{{\mathcal{T}}}}}}}}$$ T ) symmetry breaking are sought after for their anomalous physical properties, low-dissipation electronic and spin responses, and information-technology applications. Recently predicted altermagnetic phase features an unconventional and attractive combination of a strong $${{{{{{{\mathcal{T}}}}}}}}$$ T -symmetry breaking in the electronic structure and a zero or only weak-relativistic magnetization. In this work, we experimentally observe the anomalous Hall effect, a prominent representative of the $${{{{{{{\mathcal{T}}}}}}}}$$ T -symmetry breaking responses, in the absence of an external magnetic field in epitaxial thin-film Mn5Si3 with a vanishingly small net magnetic moment. By symmetry analysis and first-principles calculations we demonstrate that the unconventional d-wave altermagnetic phase is consistent with the experimental structural and magnetic characterization of the Mn5Si3 epilayers, and that the theoretical anomalous Hall conductivity generated by the phase is sizable, in agreement with experiment. An analogy with unconventional d-wave superconductivity suggests that our identification of a candidate of unconventional d-wave altermagnetism points towards a new chapter of research and applications of magnetic phases.

Abstract Cobalt monosilicide, CoSi, belongs to the new class of materials, featuring Weyl nodes in the bulk band structure, located very close to the Fermi energy. By shifting the chemical potential into these Weyl nodes using Fe‐doping, quantum effects like the chiral anomaly and weak anti localization have been evidenced. However, the behavior of these effects with respect to the doping concentration is largely unexplored. Crystal structure and the electrical transport properties in single crystalline CoSi micro‐ribbons with different Fe‐doping are studied to identify the characteristic temperatures of electronic quantum and correlation effects. For the crystal structure analysis, transmission electron microscopy and powder X‐ray diffraction analysis with a refined structural model is performed based on Le Bail fitting to analyze the lattice parameter. Hereby, the change of the lattice parameter of Co1−xFexSi is shown with increasing Fe content. In the electrical transport analysis, the occurrence of chiral anomaly and the weak anti localization effect in Fe‐doped CoSi are presented. It is shown that these effect can be tailored by Fe‐doping in CoSi.

Abstract Successful optimization of the thermoelectric (TE) performance of materials, described by the figure of merit zT, is a key enabler for its application in energy harvesting or Peltier cooling devices. While the zT value of bulk materials is accessible by a variety of commercial measurement setups, precise determination of the zT value for thin and thick films remains a great challenge. This is particularly relevant for films synthesized by electrochemical deposition, where the TE material is deposited onto an electrically conductive seed layer causing an in‐plane short circuit. Therefore, a platform for full in‐plane zT characterization of electrochemically deposited TE materials is developed, eliminating the impact of the electrically conducting seed layer. The characterization is done using a suspended TE material within a transport device which was prepared by photolithography in combination with chemical etching steps. An analytical model to determine the thermal conductivity is developed and the results verified using finite element simulations. Taken together, the full in‐plane zT characterization provides an inevitable milestone for material optimization under realistic conditions in TE devices.