Electronic and magnetic properties of the topological semimetal SmMg${}_2$Bi${}_2$

Abstract

Dirac semimetals show nontrivial physical properties and can host exotic quantum states like Weyl semimetals and topological insulators under suitable external conditions. Here, by combining angle-resolved photoemission spectroscopy measurements (ARPES) and first-principle calculations, we demonstrate that Zintl-phase compound SmMg${}_2$Bi${}_2$ belongs to the close proximity to a topological Dirac semimetallic state. ARPES results show a Dirac-like band crossing at the zone-center near the Fermi level ($E_{\mathrm{F}}$) which is further confirmed by first-principle calculations. Theoretical studies also reveal that SmMg${}_2$Bi${}_2$ belongs to a $Z_2$ topological class and hosts spin-polarized states around the $E_{\mathrm{F}}$. Zintl's theory predicts that the valence state of Sm in this material should be Sm${}^{2+}$, however we detect many Sm-4$f$ multiplet states (flat-bands) whose energy positions suggest the presence of both Sm${}^{2+}$ and Sm${}^{3+}$. It is also evident that these flat-bands and other dispersive states are strongly hybridized when they cross each other. Due to the presence of Sm${}^{3+}$ ions, the temperature dependence of magnetic susceptibility $\chi (T)$ shows Curie-Weiss-like contribution in the low temperature region, in addition to the Van Vleck-like behaviour expected for the Sm${}^{2+}$ ions. The present study will help in better understanding of the electronic structure, magnetism and transport properties of related materials.

11 pages, 7 figures

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