The search for noncentrosymmetric superconductors that may exhibit unusual physical properties and unconventional superconductivity has yielded the synthesis of a noncentrosymmetric phosphide ${\mathrm{Mg}}_2{\mathrm{Rh}}_3\mathrm{P}$ with an $\mathrm{A}{\mathrm{l}}_2\mathrm{M}{\mathrm{o}}_3\mathrm{C}$-type structure. Although stoichiometric ${\mathrm{Mg}}_2{\mathrm{Rh}}_3\mathrm{P}$ does not exhibit superconductivity at temperatures above 2 K, we found that an Mg deficiency of approximately 5 at.% in the ${\mathrm{Mg}}_2{\mathrm{Rh}}_3\mathrm{P}$-induced superconductivity at 3.9 K. Physical properties such as the lattice parameter $a=7.0881\AA$, Sommerfeld constant ${\gamma }_{\mathrm{n}}=5.36\mathrm{mJ}\mathrm{mo}{\mathrm{l}}^{-1}{\mathrm{K}}^{-2}$, specific heat jump $\mathrm{\Delta }{C}_{\mathrm{el}}/{\gamma }_{\mathrm{n}}{T}_{\mathrm{c}}=0.72$, electron–phonon coupling constant ${\lambda }_{\mathrm{e}-\mathrm{p}}=0.58$, upper critical field $H_{\mathrm{c}2}\left(0\right)=24.3\mathrm{kOe}$, and pressure effect $d{T}_{\mathrm{c}}/dP=-0.34\mathrm{K}/\mathrm{GPa}$ were measured for the superconducting ${\mathrm{Mg}}_{2-\delta }{\mathrm{Rh}}_3\mathrm{P}$ ($\delta \sim 0.1$). Band-structure calculations indicate that exotic fermions, which are not present in high-energy physics, exist in ${\mathrm{Mg}}_2{\mathrm{Rh}}_3\mathrm{P}$. Since Mg, Rh, and P are the first elements used at each crystal site of $\mathrm{A}{\mathrm{l}}_2\mathrm{M}{\mathrm{o}}_3\mathrm{C}$-type compounds, the discovery of ${\mathrm{Mg}}_2{\mathrm{Rh}}_3\mathrm{P}$ may guide the search for new related materials.

• Received 8 July 2019
• Revised 20 September 2019

DOI:https://doi.org/10.1103/PhysRevMaterials.3.124802