Anomalous angular dependence of Hc2 in CaAlSi

We have studied detailed anisotropic superconducting properties of a new layered intermetallic compound CaAlSi with AlB 2 structure grown by the floating-zone method. The anisotropy parameter γ (= H c2 ab / H c2 c ) determined from both magnetic and transport measurements is about 2.0. Despite the small value of γ , angular dependence of H c2 shows cusp-like feature for fields parallel to the superconducting plane, suggesting the presence of two-dimensional superconducting units. These apparently contradictory results can be partly explained by the presence of superstructure along c -axis. The resistivity anisotropy ( ρ c / ρ ab ) is 3.1 at room temperature, consistent with that estimated from H c2 .