Interplay of superexchange and vibronic effects in the hidden order of Ba_2MgReO_6 unravelled from first principles
arxiv(2024)
摘要
The origin of the "hidden" quadrupolar and unconventional magnetic
low-temperature orders observed in the spin-orbit double perovskite
Ba_2MgReO_6 defies explanation through standard experimental and
theoretical techniques. Here we address this problem by deriving and solving an
ab initio low-temperature effective Hamiltonian including inter-site electronic
exchange and vibronic (electron-lattice) couplings between J_eff=3/2
Jahn-Teller-active Rhenium states. Our findings disclose the nature of these
elusive states, attributing it to intertwined exchange and electron-lattice
couplings, thus diverging from the conventional dichotomy of purely electronic
or lattice driving mechanisms. Our results indicate the resilience of the
quadrupolar hidden order under pressure, yet its rapid suppression under
uniaxial strain suggests that external or lattice-induced distortions play a
pivotal role in determining the relative stability of competing phases in
Ba_2MgReO_6 and similar d^1 double perovskites.
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