De Haas-van Alphen effect in Rh₂Ga₉ and Ir₂Ga₉ without inversion symmetry in the crystal structure and related compounds T₂Al₉ (T: Co, Rh, Ir) with inversion symmetry

We succeeded in growing high-quality single crystals of Rh₂Ga₉ and Ir₂Ga₉ with the non-centrosymmetric (distorted Co₂Al₉-type) monoclinic structure by the Ga-self flux method, and carried out the de Haas-van Alphen (dHvA) experiments. The Fermi surface is found to be split into two different Fermi surfaces, reflecting the non-centrosymmetric crystal structure. A magnitude of the antisymmetric spin-orbit interaction or a splitting energy between the two Fermi surfaces are determined to be 56K for dHvA branch α and 45K for branch β in Rh₂Ga₉, where these dHvA branches correspond to main Fermi surfaces. The present splitting values are compared with 290 and 130 K in Ir₂Ga₉, respectively. The splitting energy is found to be larger in the Ir-5d conduction electrons than in the Rh-4d conduction electrons. The split dHvA branches in Rh₂Ga₉ and Ir₂Ga₉ are also compared with the single dHvA branch in Co₂Al₉, Rh₂Al₉, and Ir₂Al₉ with inversion symmetry in the crystal structure.