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Emergence of metallic surface states and negative differential conductance in thinβ-FeSi2films on Si(001)
Keisuke Sagisaka1, Tomoko Kusawake1, David Bowler2,3,4
1Research Center for Advanced Measurement and Characterization, National Institute for Materials Science, 1-2-1 Sengen, Tsukuba, Ibaraki 305-0047, Japan.
Abstract:
The electronic properties of the surface ofβ-FeSi2have been debated for a long. We studied the surface states ofβ-FeSi2films grown on Si(001) substrates using scanning tunnelling microscopy (STM) and spectroscopy (STS), with the aid of density functional theory calculations. STM simulations using the surface model proposed by Romanyuket al(2014Phys. Rev.B90155305) reproduce the detailed features of experimental STM images. The result of STS showed metallic surface states in accordance with theoretical predictions. The Fermi level was pinned by a surface state that appeared in the bulk band gap of theβ-FeSi2film, irrespective of the polarity of the substrate. We also observed negative differential conductance at ∼0.45 eV above the Fermi level in STS measurements performed at 4.5 K, reflecting the presence of an energy gap in the unoccupied surface states ofβ-FeSi2.
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