  The temperature ($T$) and magnetic field ($H$) dependence of the magnetic
penetration depth, $\lambda(T,H)$, in Ca(Al$_{0.5}$Si$_{0.5}$)$_2$ exhibits
significant deviation from that expected for conventional BCS superconductors.
In particular, it is inferred from a field dependence of $\lambda(H)$ ($\propto
H$) at 2.0 K that the quasiparticle excitation is strongly enhanced by the
Doppler shift. This suggests that the superconducting order parameter in
Ca(Al$_{0.5}$Si$_{0.5}$)$_2$ is characterized by a small energy scale
$\Delta_S/k_B\le 2$ K originating either from anisotropy or multi-gap
structure.
