The electrical conductivity of post-perovskite in Earth's D layer

Recent discovery of a phase transition from perovskite to post- perovskite suggests that the physical properties of Earth's lowermost mantle, called the D'' layer, may be different from those of the overlying mantle. We report that the electrical conductivity of ( Mg0.9Fe0.1) SiO3 post- perovskite is >10(2) siemens per meter and does not vary greatly with temperature at the conditions of the D'' layer. A post- perovskite layer above the core- mantle boundary would, by electromagnetic coupling, enhance the exchange of angular momentum between the fluid core and the solid mantle, which can explain the observed changes in the length of a day on decadal time scales. Heterogeneity in the conductivity of the lowermost mantle is likely to depend on changes in chemistry of the boundary region, not fluctuations in temperature.