Superconductivity induced by hole-doping in the nodal-line semimetal NaAlGe

Recently, correlated Dirac electron system have attracted much attention in the material research field. It is predicted that correlation effects in the nodal line bands will lead to the various ground states such as antiferromagnetic, exciton, and superconducting phases, but there are few candidate materials [1,2]. In this context, we focus on the nodal line semimetal NaAlGe which has a nodal line band near Fermi energy and an anomalously large Wilson ratio of 10. Moreover, NaAlGe exhibits semiconductive electrical conductivity at low temperatures, indicating the formation of a pseudogap at approximately100 K; the origin of the pseudogap in NaAlGe may be associated with excitonic instability [3].

In this work, we investigated hole-doping effects on the ground state of the solid solution Na(Al_1–xZn_x)Ge by electrical resistivity, magnetic susceptibility, and heat capacity measurements. It found that the pseudogap is suppressed continuously with increasing Zn content, followed by the appearance of a superconducting dome with the highest transition temperature of 2.8 K. This superconductivity most likely results from excitonic fluctuations.