Structurally triggered orbital and charge orderings in TlMnO₃ and related compounds

Metal insulator transition with C-type orbital ordering (OO) is generic among RMn³⁺O₃(R=rare earth) perovskites with a $Pbnm$ ground state. Distinctly, TlMnO₃ shows a very different rocksalt (G-type) OO together with the emergence of an unusual triclinic P1̄ structure. Employing first principles calculations, and symmetry mode analysis we investigated structural and electronic origin of G-type OO in TlMnO₃. We reveal that Jahn-Teller (JT) distortion in TlMnO₃ is structurally triggered, consequently giving rise to G type OO. Similar mechanism is rather common in RNi³⁺O₃ perovskites, where breathing of NiO₆ is observed. We further reveal that, triggering of breathing distortion is not limited to nickelates but also present in TlMnO₃ (and LaMnO₃). In fact, other types of JT distortion, are also show triggering mechanism, although final ground state of these systems result from subtle anharmonic interactions.