Superstructure-dependent electronic states in CaAlSi superconductors studied by angle-resolved photoemission spectroscopy.

We have performed high-resolution angle-resolved photoemission spectroscopy on layered polymorph series of 1H-, 5H-, and 6H-CaAlSi, which exhibit superconductivity below 6.5, 5.7, and 7.7 K, respectively. While the overall band structure in the valence-band region is similar among these compounds, the volume of the Fermi surface at the M point and the magnitude of the superconducting gap are markedly different from each other. Implications of such variation in the electronic structure due to the superstructure along the c axis are discussed in relation to the physical properties of CaAlSi. [ABSTRACT FROM AUTHOR]