Seminar : Multipolar orders in spin-orbit entangled 5d Mott insulators
Dr. Daigorou Hirai from Institute for Solid State Physics, University of Tokyo
Multipolar orders in spin-orbit entangled 5d Mott insulators
In electronic solids with strong spin–orbit interactions (SOIs), the spin and orbital degrees of freedom of an electron are quantum mechanically entangled, which may result in an exotic multipolar order instead of a conventional dipolar order such as a magnetic order . Such a higher-degree order is called “hidden order” because of difficulties in experimental detection. Moreover, the number of candidate compounds is limited, especially rare in d electron systems, in which an interplay between SOIs and Coulomb interactions is expected to cause rich physics. Here, we employ state-of-the-art synchrotron X-ray diffraction techniques on a high-quality single crystal to probe subtle symmetry breaking induced by a multipolar order. We unequivocally demonstrate that the double-perovskite Ba2MgReO6 exhibits successive transitions to quadrupolar and then dipolar orders upon cooling, which is consistent with a theory considering SOIs [2,3]. Our findings are a first step towards understanding the intriguing physics of multipoles realized by spin–orbit-entangled 5d electrons.
 G. Chen et al., Phys. Rev. B 82, 174440 (2010).
 D. Hirai et al., J. Phys. Soc. Jpn. 88, 064712 (2019).
 D. Hirai et al., Phys. Rev. Research 2, 022063(R) (2020).
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