Superconductivity induced by Mg deficiency in non-centrosymmetric phosphide Mg${}_2$Rh${}_3$P

The search for non-centrosymmetric superconductors that may exhibit unusual physical properties and unconventional superconductivity has yielded the synthesis of a non-centrosymmetric phosphide Mg${}_2$Rh${}_3$P with an Al${}_2$Mo${}_3$C-type structure. Although stoichiometric Mg${}_2$Rh${}_3$P does not exhibit superconductivity at temperatures above 2 K, we found that an Mg deficiency of approximately 5 at.% in the Mg${}_2$Rh${}_3$P induced superconductivity at 3.9 K. Physical properties such as the lattice parameter a = 0.70881 nm, Sommerfeld constant ${\gamma }_n$ = 5.36 mJ mol${}^{-1}$ K${}^{-2}$, specific heat jump $\mathrm{\Delta }$C${}_{el}$/${\gamma }_n$Tc = 0.72, electron-phonon coupling constant $\lambda$${}_{e-p}$ = 0.58, upper critical field H${}_{c2}$(0) = 24.3 kOe, and pressure effect dTc/dP = -0.34 K/GPa were measured for the superconducting Mg${}_{2-\delta }$Rh${}_3$P ($\delta$ $\sim$ 0.1). Band-structure calculations indicate that exotic fermions, which are not present in high-energy physics, exist in Mg${}_2$Rh${}_3$P. Since Mg, Rh, and P are the first elements used at each crystal site of Al${}_2$Mo${}_3$C-type compounds, the discovery of Mg${}_2$Rh${}_3$P may guide the search for new related materials.