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Tuning MgB<inf>2</inf>(0001) surface states through surface termination

Abstract:

Surface state localization and hybridization on B, Mg, and Li terminated MgB2(0001) surfaces are studied within density functional theory (DFT). For the B terminated surface we find a low energy B σ1 surface state, a spz surface state, and B σ2 and σ3 quantum well states, which are 90% localized in the topmost B layer. Our results demonstrate that by charging the B atomic layer, either by changing the surface termination or through electro-chemical doping, the B σ surface states are shifted down in energy, filled, and delocalize through hybridization as they cross the bulk MgB2 bulk bands. On the other hand, the spz surface state should be shifted up in energy, emptied, and gain an increasingly metallic s character by adding a Mg, Mg +1, or Li terminating atomic layer. These results clearly show both the robust nature of MgB2(0001) surface states, and how their localization and energy range may be tuned by surface termination and charging, with implications for the superconducting and plasmonic behavior of MgB 2. © 2011 American Physical Society.