Electronic bound states in the continuum in a two-dimensional metal

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Abstract
Bound states in the continuum (BICs) are quantum states that remain localized despite lying within a continuum of extended, delocalized states. Whereas optical BICs have been realized in photonic systems, achieving electronic bound states embedded in a metallic background remains an ongoing challenge. In this study, we used scanning tunneling microscopy to identify two defect-induced electronic states that remain localized within the metallic continuum of Pd 5 AlI 2 , a two-dimensional van der Waals metal. Our calculations suggest that electron-hopping interference on the decorated checkerboard lattice of Pd 5 AlI 2 gives rise to a (quasi) flat band built from spatially localized eigenstates that are orthogonal to the dispersive continuum. Atomic defects within this frustrated lattice shift the associated flat-band localized states into the metallic continuum, forming robust, symmetry-protected BICs.
Funding Information
  • National Science Foundation (DMR-2340394)
  • U.S. Department of Energy (DE-SC0019443)
  • Air Force Office of Scientific Research (FA9550-22-1-0389)
  • Air Force Office of Scientific Research (FA9550-21-1-0378)
  • Materials Research Science and Engineering Center, Columbia University, New York (DMR-2011738)
  • Lilly Endowment, Inc.
  • Brown Institute for Basic Science

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