Metallic layer inside the Earth's lower mantle

We predict the insulator-metal-insulator transitions for the temperature and pressure of the lower mantle with the metal layer thickness $\Delta h\approx 400$ km at the depth of 1400–1800 km. The insulator-metal transition has the Mott–Hubbard origin, while the second transition from metal to insulator results from spin crossover of the Fe$^{2+}$ ions from high spin $S=2$ to low spin $S=0$ state. The conductivity in the metal layer may attain $250$ S/m. The depth profile of the conductivity is also suggested.