Berlin 2024 – wissenschaftliches Programm

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MA: Fachverband Magnetismus

MA 4: Magnetic Heusler Compounds and Complex Magnetic Oxides

MA 4.8: Vortrag

Montag, 18. März 2024, 11:30–11:45, EB 107

Janh-Teller bipolarons in the spin-orbit multipolar magnetic oxide Ba₂NaOsO₆ — •Lorenzo Celiberti¹ and Cesare Franchini^1,2 — ¹Faculty of Physics and Center for Computational Materials Science, University of Vienna, Vienna, Austria — ²Department of Physics and Astronomy ’Augusto Righi’, University of Bologna, Bologna, Italy

Complex oxides hosting 5d electrons present a variety of exotic phases arising from spin-orbital (SO) interactions and electronic correlation (EC). In the Mott insulator Ba₂NaOsO₆ (BNOO), a canted antiferromagnet with multipolar interactions, strong EC together with Jahn-Teller lattice activity pave the way for bridging polarons and SO coupling, distinct quantum effects that play a critical role in charge transport and spin-orbitronics. Polarons are quasiparticles originating from strong electron-phonon interaction and are ubiquitous in polarizable materials, especially in 3d transition metal oxides. Despite the more spatially delocalized nature of 5d electrons, we demonstrate the formation of Jahn-Teller spin-orbital bipolarons in electron doped BNOO by combining ab-initio calculations with nuclear magnetic resonance and muon spin rotation measurements. The polaronic charge trapping process converts the Os 5d¹ spin-orbital J_eff=3/2 levels, characteristic of pristine BNOO, into a 5d² J_eff=2 manifold, leading to the coexistence of different J-effective states in a single-phase material. Moreover, we suggest that polaron formation creates robust in-gap states that prevent the transition to a metal phase even at ultrahigh doping, thus preserving the Mott gap across the entire doping range.

Keywords: polarons; spin-orbit coupling; Jahn-Teller