Spin-orbit coupling effects on spin-phonon coupling in Cd2Os2O7

Abstract

Spin-orbit coupling (SOC) is essential in understanding the properties of 5d transition metal compounds, whose SOC value is large and almost comparable to other key parameters. Over the past few years, there have been numerous studies on the SOC-driven effects of the electronic bands, magnetism, and spin-orbit entanglement for those materials with a large SOC. However, it is less studied and remains an unsolved problem in how the SOC affects the lattice dynamics. We, therefore, measured the phonon spectra of 5d pyrochlore Cd 2 Os 2 O 7 over the full Brillouin zone to address the question by using inelastic x-ray scattering (IXS). Our main finding is a visible mode-dependence in the phonon spectra, measured across the metal-insulator transition at 227 K. We examined the SOC strength dependence of the lattice dynamics and its spin-phonon (SP) coupling, with first-principle calculations. Our experimental data taken at 100 K are in good agreement with the theoretical results obtained with the optimized U = 2.0 eV with SOC. By scaling the SOC strength and the U value in the DFT calculations, we demonstrate that SOC is more relevant than U to explaining the observed mode-dependent phonon energy shifts with temperature. Furthermore, the temperature dependence of the phonon energy can be effectively described by scaling SOC. Our work provides clear evidence of SOC producing a non-negligible and essential effect on the lattice dynamics of Cd 2 Os 2 O 7 and its SP coupling.

Optoelectronic performance of perovskite Cs2KMI6 (M = Ga, In) based on high-throughput screening and first-principles calculations

“…3, the band structures based on the HSE06 functional are close to ones with the HSE06 + SOC functional. The SOC effects are usually proposed to be evaluated to analyze the properties of 5d transition metal compounds, 51 for instance, the electronic properties of compounds containing heavy elements such as Pb and Bi. 48,49 Therefore, by taking into account the relatively light elements contained in Cs 2 KMI 6 (M = Ga, In), 48,49 and calculated similar band structures by HSE06 and HSE06 + SOC functionals (Fig.…”

The physical significance of imaginary phonon modes in crystals

“…We have seen above how chemical bonding determines the supercell size (or q-point grid) required for accurate predictions. Other material-specific properties to consider when calculating the Φ and D(q) include the include the extent of electron correlation [53,54] and spin-phonon coupling [55,56]. We address curing of imaginary phonons emerging from these phenomena in table 1.…”

Noncollinear DFT+U and Hubbard parameters with fully relativistic ultrasoft pseudopotentials

“…The inclusion of the Hubbard correction successfully stabilizes all three AI/AO, 3I/1O, and 2I/2O magnetic and insulating states. The calculated U Os = 4.48 eV, including the effect of SOC, is considerably larger than the empirical range 0.8-2 eV used in previous ab initio studies [61,64]; therefore, the resulting band gap is expectedly larger, but the magnetic moments FIG. 3.…”