Effect of pressure on superconductivity in NaAlSi

The ternary superconductor NaAlSi, isostructural with LiFeAs, the ``111'' iron pnictide superconductor, is investigated under pressure. The structure remains stable up to 15 GPa. Resistivity and susceptibility measurements show an increase of ${T}_{c}$ up to 2 GPa, followed by a decrease until superconductivity disappears at 4.8 GPa. Band structure calculations show that pressure should have a negligible effect on the electronic structure and the Fermi surface and thus the disappearance of superconductivity under pressure must have a different origin. We compare the electronic structure of NaAlSi under pressure with that of nonsuperconducting isostructural NaAlGe.