Fate of multipolar physics in $5d^2$ double perovskites

Abstract

In a cubic environment, the ground state of spin-orbit coupled $5d^2$ ions is a non-Kramers $E_g$ doublet, which hosts quadrupole and octupole moments. A series of $5d^2$ osmium double perovskites Ba${}_{2}M$OsO${}_6$ (M = Mg, Ca, Zn, Cd) have recently been proposed to exhibit multipolar orders. We investigate the structural properties of these materials using $\text{ab}$-$\text{initio}$ calculations and find that the cubic structure is unstable for the Cd compound while the Mg, Ca, and Zn materials retain $Fm\bar{3}m$ symmetry. We show that Ba${}_2$CdOsO${}_6$ favours a rhombohedral $R\bar{3}$ structure characterized by $a^{-}{a}^{-}{a}^{-}$ octahedral tiltings as indicated by unstable ${\mathcal{T}}_{1g}$ phonon modes. Trigonal distortions split the excited $T_{2g}$ triplet into an $E_g^{\prime }$ doublet and an $A_g$ singlet, which may cross energy levels with the $E_g$ doublet and suppress the multipolar physics. We find a window where $E_g$ remains the lowest energy state under trigonal distortion, enabling the emergence of multipole phases in non-cubic crystal environments.

9 pages, 6 figures, journal version with minor revisions

References in corpus (14)

• Heavy Fermion Superconductivity in the Quadrupole Ordered State of PrV2Al20
• Spin-orbit-entangled electronic phases in 4$d$ and 5$d$ transition-metal compounds
• Detection of multipolar orders in the spin-orbit-entangled 5d Mott insulator Ba2MgReO6
• Successive Symmetry Breaking in a Jeff = 3/2 Quartet in the Spin-Orbit Coupled Insulator Ba2MgReO6
• Exchange interactions, Jahn-Teller coupling, and multipole orders in pseudospin one-half $5{\mathbf{d}}^2$ Mott insulators
• Ferro-octupolar order and low-energy excitations in d${}^2$ double perovskites of Osmium
• Magnetism in S=1/2 Double-Perovskites with Strong Spin-Orbit Interactions
• Sleuthing Hidden Order
• Modelling Magnetic Multipolar Phases in Density Functional Theory
• Octupolar order and Ising quantum criticality tuned by strain and dimensionality: Application to $d$-orbital Mott insulators
• Triple-$q$ quadrupole-octupole order scenario for PrV${}_2$Al${}_{20}$
• Lone octupole and bulk magnetism in osmate 5d2 double perovskites
• Field-induced Kitaev multipolar liquid in spin-orbit coupled $d^2$ honeycomb Mott insulators
• Interplay between quadrupolar and magnetic interactions in 5$d^1$ double perovskite Ba${}_2$MgReO${}_6$ under pressure

Cited by in corpus (5)

• Hidden orders in spin-orbit entangled correlated insulators
• Spin-orbit-entangled electronic structure of Ba${}_2$CaOsO${}_6$ studied by O $K$-edge resonant inelastic X-ray scattering
• Dipolar and quadrupolar correlations in the $5d^2$ Re-based double perovskites Ba${}_2$YReO${}_6$ and Ba${}_2$ScReO${}_6$
• Emergence of quadrupolar order under magnetic field in $5d^2$ double perovskites
• Polaron-driven switching of octupolar order in doped 5d${}^2$ double perovskite