Comparative study of anisotropic superconductivity in CaAlSi and CaGaSi

In order to get some insight into the origin of the anomalous angular dependence of Hc2 in a layered intermetallic compound CaAlSi, electronic, superconducting, and structural properties are compared between CaAlSi and CaGaSi. The angular dependence of Hc2 in CaGaSi is well described by the anisotropic GL model. Parallel to this finding, the pronounced lattice modulation accompanying the superstructure along the c-axis in CaAlSi is absent in CaGaSi. A relatively large specific heat jump at the superconducting transition in CaAlSi compared with CaGaSi indicates the presence of strong electron-phonon coupling in CaAlSi, which may cause the superstructure and the anomalous angular dependence of Hc2.