Observation of superconductivity and its enhancement at the charge density wave critical point in LaAgSb2

We discover superconductivity (SC) in LaAgSb2 at ambient pressure and its close correlation with a charge density wave (CDW) under pressure. The superconducting transition temperature (Tc) exhibits a sharp peak at a CDW critical pressure of 3.2 GPa. We demonstrate that the carriers inhabiting the Sb-square net are crucial not only in the formation of CDW but also in SC for their relatively strong electron-phonon coupling (EPC). Furthermore, theoretical EPC strength in pristine LaAgSb2 cannot explain the observed peak with Tc∼1 K, which indicates that an additional mechanism reinforces SC only around the CDW critical pressure.