28 August 2023 Mon 4 pm

Complex oxides hosting 5d electrons present a variety of exotic phases arising from spin-orbital (SO) interactions and electronic correlation (EC) [1]. In the Mott insulator Ba2NaOsO6, a canted antiferromagnet with multipolar interactions [2], strong EC together with Jahn-Teller (JT) 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 [3, 4]. Polarons are quasiparticles originating from strong electron-phonon interaction and are ubiquitous in polarizable materials, especially in 3d transition metal oxides [3]. Despite the more spatially delocalized nature of 5d electrons, we demonstrate the formation of Jahn-Teller spin-orbital polarons in electron doped Ba2Na1−xCaxOsO6 by combining ab-initio calculations with nuclear magnetic resonance and muon spin rotation measurements. The polaronic charge trapping process converts the Os 5d1 spinorbital Jeff = 3/2 levels, characteristic of pristine BNOO, into a 5d2 Jeff = 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 from d 1 BNOO to d 2 Ba2CaOsO6.

[1] J. G. Rau, E. K.-H. Lee, and H.-Y. Kee, Annual Review of Condensed Matter Physics 7, 195 (2016).

[2] D. Fiore Mosca, L. V. Pourovskii, B. H. Kim, P. Liu, S. Sanna, F. Boscherini, S. Khmelevskyi, and C. Franchini, Physical Review B 103, 104401 (2021).

[3] C. Franchini, M. Reticcioli, M. Setvin, and U. Diebold, Nature Reviews Materials, 1 (2021).

[4] A. Soumyanarayanan, N. Reyren, A. Fert, and C. Panagopoulos, Nature 539, 509 (2016).

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