Crystal Growth and Characterization of the Topological Superconductor Candidate RhPb₂ and its Related Compounds

Until now, there have been only few reports on the binary compound RhPb₂ [1-3]. Havinga <i>et al.</i> suggested the Pb deficient structure of RhPb_1.9 in their polycrystal samples with C16 tetragonal structure. Zhang <i>et al. </i>recently predicted that β-RhPb₂must have a topological nature according to their band calculation. We have successfully grown RhPb₂ crystals from the Pb-rich melt (Rh:Pb=1:8) by the slow cooling process in a steep temperature gradient infrared mirror furnace followed by the Pb-Rh binary phase diagram [4], where RhPb₂ grows through peritectic reaction incongruently between 320 ^○C and 640 ^○C.<br/><br/>Detailed single crystal X-ray diffraction analysis showed that RhPb₂belongs to the <i>I</i>4/mcm space group with lattice parameters a=6.7068(4) Å and c=$5.8623(6) Å which agrees with Gendron and Jones [2], and Havinga <i>et al.</i> [3] (polycrystal analysis) but does not with the work by Zhang <i>et al.</i> [1], because their RhPb₂ is assumed to be β-RhPb₂, which seems to belong to the <i>I</i>4/mmm space group. Our single crystal analysis showed slight deficiency in Rh atoms (0.950(9)) while in Havinga <i>et al.</i> [3] slight Pb deficiency was observed.<br/><br/>According to the recent band calculation [5] including the spin-orbit coupling RhPb₂ is considered to be a candidate of topological Weyl (semi)metal and may undergo to the superconducting state at 2.66 K [2]. In order to study such an interesting topological Weyl superconductor RhPb₂, we performed the resistivity and superconducting properties such as the critical currents, the critical fields <i>H</i>_c1 and <i>H</i>_c2 measurements and the Hall measurements. Besides RhPb₂, the similar compounds such as single crystals of AuPb₂ and Au₂Pb have also been synthesized in order for comparison.<br/><br/>[1] J. F. Zhang <i>et al.</i>, Phys. Rev. <b>B99</b> (2019) 045110.<br/><br/>[2] M. F. Gendron and R. E. Jones, J. Phys. Chem. Solids, <b>23 </b>(1962) 405.<br/><br/>[3] E.E. Havinga, H. Damsma, J. Kanis, J. Less Common Metals, <b>27</b> (1972) 281-291.<br/><br/>[4]“<i>Phase Equilibria, Crystallographic and Thermodynamic Data of Binary Alloy, Pb-Rh (Lead-Rhodium)</i>", Landolt-Börnstein -Group IV Physical Chemistry <b>5I</b> (1998) 321.<br/><br/>[5] QuanSheng Wu, Gabriel Autès, Nicolas Mounet, Oleg V. Yazyev, TopoMat: a database of high-throughput first-principles calculations of topological materials, Materials Cloud Archive <b>0019/v1</b>(2019), doi: 10.24435/materialscloud:2019.0019/v1.