Cubic 5d1 double perovskites are geometrically frustrated multipolar systems and exhibit various ordered phases. The most established phase is the canted antiferromagnetic phase found in Ba2NaOsO6 and Ba2MgReO6 at low temperatures. Spin-orbit exchange theory describes well the phase. Nevertheless, the theory does not explain all of the ordered phases found in 5d1 double perovskites. In Cs2TaCl6, an antiferromagnetic phase with a ferro-quadrupolar order develops. In Ba2MgReO6, two quadrupolar orderings coexist above the magnetic transition temperature.
These puzzles could be resolved based on the spin-orbit-lattice entanglement driven by the spin-orbit and electron-phonon couplings on 5d1 metal sites. We proposed ab initio the development of spin-orbit-lattice entangled states in osmates [1]. On this basis, we showed that the ordering of the spin-orbit-lattice entangled states explains the puzzling ordered phases in the Ta and Re compounds [2]. Recently, we confirmed the presence of the spin-orbit-lattice entangled states in the Re compounds by theoretically analyzing the Re L3-edge and O K-edge RIXS spectra [3, 4]. In my talk, I will present the theory of spin-orbit-lattice entangled states in 5d1 double perovskites and theoretical analysis of the RIXS spectra.
[1] N. Iwahara, V. Vieru, and L. F. Chibotaru, Phys. Rev. B 98, 075138 (2018).
[2] N. Iwahara and L. F. Chibotaru, Phys. Rev. B 107, L220404 (2023).
[3] F. I. Frontini et al., Phys. Rev. Lett. 133, 036501 (2024).
[4] N. Iwahara et al., submitted.