Polar catastrophe and the spin-polarized electron gas at the interface
(Color online) Crystal structure of the superlattice. Only one of the two identical interfaces occurring in the superlattice is shown. The arrows indicate the alignment of Mn core spins in the ground state magnetic configuration. The shadow indicates schematically the formation of the two-dimensional electron gas, which extends to several layers on either side of the interface.
Occupancy of the Mn orbitals in the individual layers near the interface, indicating the accumulation of extra electrons at the interface and the electron leakage from the LMO to the SMO side. The inset shows the layerwise variation of the energy of the lowest states as obtained from the LMTO “fat bands” in the band structure, which is indicative of the net potential experienced by the electrons across the interface.
Density-functional results for the layer-projected majority (↑) and minority (↓) spin densities of states for the superlattice. The innermost layers away from the interface, both in LMO and SMO, already show the bulk-like insulating behavior of the respective materials. Layers close to the interface are half-metallic, populated by spin-polarized electrons.
Charge density contours near the interface, plotted on the -plane, which is normal to the interface. Left panel is indicative of the total electron density, a small amount of which leaks from the LMO to the SMO side. Right panel shows the charge density of the electron states at the Fermi energy, which are confined in the interface region and are made up of majority-spin states only, consistent with the middle panel of Fig. 3. The charge densities correspond to an energy window below the Fermi energy (left panel from to and the right panel from to ). Contour values are logarithmic: , where and for the left panel and and for the right panel, where takes integral values.
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