Free surfaces recast superconductivity in few-monolayer MgB2: Combined first-principles and ARPES demonstration

J. Bekaert, L. Bignardi, A. Aperis, P. van Abswoude, C. Mattevi, S. Gorovikov, L. Petaccia, A. Goldoni, B. Partoens, P. M. Oppeneer, F. M. Peeters, M. V. Milosevic, P. Rudolf, C. Cepek

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Abstract

Two-dimensional materials are known to harbour properties very different from those of their bulk counterparts. Recent years have seen the rise of atomically thin superconductors, with a caveat that superconductivity is strongly depleted unless enhanced by specific substrates, intercalants or adatoms. Surprisingly, the role in superconductivity of electronic states originating from simple free surfaces of two-dimensional materials has remained elusive to date. Here, based on first-principles calculations, anisotropic Eliashberg theory, and angle-resolved photoemission spectroscopy (ARPES), we show that surface states in few-monolayer MgB2 make a major contribution to the superconducting gap spectrum and density of states, clearly distinct from the widely known, bulk-like sigma-and pi-gaps. As a proof of principle, we predict and measure the gap opening on the magnesium-based surface band up to a critical temperature as high as similar to 30 K for merely six monolayers thick MgB2. These findings establish free surfaces as an unavoidable ingredient in understanding and further tailoring of superconductivity in atomically thin materials.

Original languageEnglish
Article number14458
Number of pages12
JournalScientific Reports
Volume7
DOIs
Publication statusPublished - 31-Oct-2017

Keywords

  • GRAPHENE
  • FILMS
  • HETEROSTRUCTURES
  • MONOCHROMATOR
  • CRYSTALS
  • BEAMLINE
  • ELETTRA
  • METALS
  • ORIGIN
  • LIMIT

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