Field-Induced Quasiparticle Excitation in Ca(Al$_{0.5}$Si$_{0.5}$)$_2$:   Evidence for unconventional Superconductivity
  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. 
S. Kuroiwa, H Takagiwa, M. Yamazawa, J. Akimitsu, K. Ohishi, A. Koda,   W. Higemoto and R. Kadono