Superconducting high pressure CaSi2 phase with Tc up to 14 K

We have studied the occurrence of superconductivity under pressure in the CaSi2 family of compounds, namely the semimetallic trigonal phase and the alpha-ThSi2-type tetragonal one. Although only the latter is superconducting (T-c = 1.56 K) at ambient pressure, starting from the trigonal phase and applying high pressure (>12 GPa) we have found a new superconducting phase with T-c(onset) similar to 14 K, among the highest ever found in silicon based materials.