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We report superconductivity in the novel 112-type iron-based compound Ca1-xLaxFeAs2. Single-crystal X-ray diffraction analysis revealed that the compound crystallizes in a monoclinic structure (space group P21), in which Fe2As2 layers alternate with Ca2As2 spacer layers such that monovalent arsenic forms zigzag chains. Superconductivity with a transition temperature (Tc) of 34 K was observed for the x = 0.1 sample, while the x = 0.21 sample exhibited trace superconductivity at 45 K. First-principles band calculations demonstrated the presence of almost cylindrical Fermi surfaces, favorable for the high Tc in La-doped CaFeAs2.
Katayama et al. (Wed,) studied this question.