Emergence of Subdominant Quadrupolar Order in the 5d2 Multipolar Mott Insulator Ba2CaOsO6
Abstract
Relativistic 5d Mott insulators host a rich variety of exotic hidden multipolar order, whose microscopic nature remains heavily debated. A broken local point-symmetry (BLPS) phase followed by antiferromagnetism was previously observed in the doped compound Ba2Na0.1Ca0.9OsO6, where mixed Os valence places the system toward the 5d2 end of the 5d1-5d2 regime. In contrast, pristine 5d2 Ba2CaOsO6 has shown a single octupolar transition with average cubic symmetry, raising the question of whether BLPS arises from chemical disorder in the doped systems. Here, we discover the BLPS phase in pristine Ba2CaOsO6 emerging at T* ≈ 50 K, precisely coincident with the octupolar transition. Beyond standard 43Ca nuclear magnetic resonance (NMR) spectral analysis, our spin-echo nutation measurements detect a finite electric field gradient, demonstrating spontaneous symmetry breaking despite the cubic average structure. While our NMR data support the previously identified octupolar order, the BLPS phase reveals a subdominant quadrupolar contribution, establishing that the hidden order in Ba2CaOsO6 is intrinsically multicomponent. Such mixed multipolar states lie beyond conventional theoretical descriptions of the 5d2 ground state. Our results establish local symmetry breaking as an intrinsic property of the clean 5d2 limit and provide a new constraint on microscopic theories of strongly spin-orbit-coupled Mott insulators.
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BibTeX
@misc{nikolov2026emergence,
title = {{Emergence of Subdominant Quadrupolar Order in the 5$d^2$ Multipolar Mott Insulator Ba$_2$CaOsO$_6$}},
author = {Ilija K. Nikolov and Giuseppe Allodi and Ginevra Corsale and Anshu Kataria and Cierra Foster and Patrick Woodward and Samuele Sanna and Vesna F. Mitrović},
howpublished = {arXiv},
year = {2026},
month = sep,
doi = {10.48550/arxiv.2609.14223},
eprint = {2609.14223},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2609.14223},
note = {CC BY-NC-SA 4.0},
}
RIS
TY - UNPB
TI - Emergence of Subdominant Quadrupolar Order in the 5d^2 Multipolar Mott Insulator Ba_2CaOsO_6
AU - Ilija K. Nikolov
AU - Giuseppe Allodi
AU - Ginevra Corsale
AU - Anshu Kataria
AU - Cierra Foster
AU - Patrick Woodward
AU - Samuele Sanna
AU - Vesna F. Mitrović
PY - 2026
DA - 2026/09/13
PB - arXiv
DO - 10.48550/arxiv.2609.14223
UR - https://arxiv.org/abs/2609.14223
AB - Relativistic 5d Mott insulators host a rich variety of exotic hidden multipolar order, whose microscopic nature remains heavily debated. A broken local point-symmetry (BLPS) phase followed by antiferromagnetism was previously observed in the doped compound Ba_2Na_0.1Ca_0.9OsO_6, where mixed Os valence places the system toward the 5d^2 end of the 5d^1-5d^2 regime. In contrast, pristine 5d^2 Ba_2CaOsO_6 has shown a single octupolar transition with average cubic symmetry, raising the question of whether BLPS arises from chemical disorder in the doped systems. Here, we discover the BLPS phase in pristine Ba_2CaOsO_6 emerging at T^* ≈ 50 K, precisely coincident with the octupolar transition. Beyond standard ^43Ca nuclear magnetic resonance (NMR) spectral analysis, our spin-echo nutation measurements detect a finite electric field gradient, demonstrating spontaneous symmetry breaking despite the cubic average structure. While our NMR data support the previously identified octupolar order, the BLPS phase reveals a subdominant quadrupolar contribution, establishing that the hidden order in Ba_2CaOsO_6 is intrinsically multicomponent. Such mixed multipolar states lie beyond conventional theoretical descriptions of the 5d^2 ground state. Our results establish local symmetry breaking as an intrinsic property of the clean 5d^2 limit and provide a new constraint on microscopic theories of strongly spin-orbit-coupled Mott insulators.
ER -